Abstraction: Showing the essential and hiding the non-Essential is known as Abstraction.
Encapsulation: The Wrapping up of data and functions into a single unit is known as Encapsulation.
Encapsulation is the term given to the process of hiding the implementation details of the object. Once an object is encapsulated, its implementation details are not immediately accessible any more. Instead they are packaged and are only indirectly accessed via the interface of the object.
Inheritance: is the Process by which the Obj of one class acquires the properties of Obj’s another Class.
A reference variable of a Super Class can be assign to any Sub class derived from the Super class.
Inheritance is the method of creating the new class based on already existing class , the new class derived is called Sub class which has all the features of existing class and its own, i.e sub class.
Adv: Reusability of code , accessibility of variables and methods of the Base class by the Derived class.
Polymorphism: The ability to take more that one form, it supports Method Overloading & Method Overriding.
Method overloading: When a method in a class having the same method name with different arguments (diff Parameters or Signatures) is said to be Method Overloading. This is Compile time Polymorphism.
o Using one identifier to refer to multiple items in the same scope.
Method Overriding: When a method in a Class having same method name with same arguments is said to be Method overriding. This is Run time Polymorphism.
o Providing a different implementation of a method in a subclass of the class that originally defined the method.
1. In Over loading there is a relationship between the methods available in the same class ,where as in Over riding there is relationship between the Super class method and Sub class method.
2. Overloading does not block the Inheritance from the Super class , Where as in Overriding blocks Inheritance from the Super Class.
3. In Overloading separate methods share the same name, where as in Overriding Sub class method replaces the Super Class.
4. Overloading must have different method Signatures , Where as Overriding methods must have same Signatures.
Dynamic dispatch: is a mechanism by which a call to Overridden function is resolved at runtime rather than at Compile time , and this is how Java implements Run time Polymorphism.
Dynamic Binding: Means the code associated with the given procedure call is not known until the time of call the call at run time. (it is associated with Inheritance & Polymorphism).
Bite code: Is a optimized set of instructions designed to be executed by Java-run time system, which is called the Java Virtual machine (JVM), i.e. in its standard form, the JVM is an Interpreter for byte code.
JIT- is a compiler for Byte code, The JIT-Complier is part of the JVM, it complies byte code into executable code in real time, piece-by-piece on demand basis.
Final classes : String, Integer , Color, Math
Abstract class : Generic servlet, Number class
o variable:An item of data named by an identifier.Each variable has a type,such as int or Object,and a scope
o class variable :A data item associated with a particular class as a whole--not with particular instances of the class. Class variables are defined in class definitions. Also called a static field. See also instance variable.
o instance variable :Any item of data that is associated with a particular object. Each instance of a class has its own copy of the instance variables defined in the class. Also called a field. See also class variable.
o local variable :A data item known within a block, but inaccessible to code outside the block. For example, any variable defined within a method is a local variable and can't be used outside the method.
o class method :A method that is invoked without reference to a particular object. Class methods affect the class as a whole, not a particular instance of the class. Also called a static method. also instance method.
o instance method :Any method that is invoked with respect to an instance of a class. Also called simply a method. See also class method.
Interface: Interfaces can be used to implement the Inheritance relationship between the non-related classes that do not belongs to the same hierarchy, i.e. any Class and any where in hierarchy. Using Interface, you can specify what a class must do but not how it does.
A class can implement more than one Interface.
An Interface can extend one or more interfaces, by using the keyword extends.
All the data members in the interface are public, static and Final by default.
An Interface method can have only Public, default and Abstract modifiers.
An Interface is loaded in memory only when it is needed for the first time.
A Class, which implements an Interface, needs to provide the implementation of all the methods in that Interface.
If the Implementation for all the methods declared in the Interface are not provided , the class itself has to declare abstract, other wise the Class will not compile.
If a class Implements two interface and both the Intfs have identical method declaration, it is totally valid.
If a class implements two interfaces both have identical method name and argument list, but different return types, the code will not compile.
An Interface can’t be instantiated. Intf Are designed to support dynamic method resolution at run time.
An interface can not be native, static, synchronize, final, protected or private.
The Interface fields can’t be Private or Protected.
A Transient variables and Volatile variables can not be members of Interface.
The extends keyword should not used after the Implements keyword, the Extends must always come before the Implements keyword.
A top level Interface can not be declared as static or final.
If an Interface species an exception list for a method, then the class implementing the interface need not declare the method with the exception list.
If an Interface can’t specify an exception list for a method, the class can’t throw an exception.
If an Interface does not specify the exception list for a method, the class can not throw any exception list.
The general form of Interface is
Access interface name {
return-type method-name1(parameter-list);
type final-varname1=value;
}
-----------------------
Marker Interfaces : Serializable, Clonable, Remote, EventListener,
Java.lang is the Package of all classes and is automatically imported into all Java Program
Interfaces: Clonable , Comparable, Runnable
Abstract Class: Abstract classes can be used to implement the inheritance relationship between the classes that belongs same hierarchy.
Classes and methods can be declared as abstract.
Abstract class can extend only one Class.
If a Class is declared as abstract , no instance of that class can be created.
If a method is declared as abstract, the sub class gives the implementation of that class.
Even if a single method is declared as abstract in a Class , the class itself can be declared as abstract.
Abstract class have at least one abstract method and others may be concrete.
In abstract Class the keyword abstract must be used for method.
Abstract classes have sub classes.
Combination of modifiers Final and Abstract is illegal in java.
Abstract Class means - Which has more than one abstract method which doesn’t have method body but at least one of its methods need to be implemented in derived Class.
The general form of abstract class is :
abstract type name (parameter list);
The Number class in the java.lang package represents the abstract concept of numbers. It makes sense to model numbers in a program, but it doesn't make sense to create a generic number object.
Difference Between Interfaces And Abstract class ?
o All the methods declared in the Interface are Abstract, where as abstract class must have atleast one abstract method and others may be concrete.
o In abstract class keyword abstract must be used for method, where as in Interface we need not use the keyword for methods.
o Abstract class must have Sub class, where as Interface can’t have sub classes.
o An abstract class can extend only one class, where as an Interface can extend more than one.
What are access specifiers and access modifiers ?
Accesss specifiers Access modifiers
Public Public
Protected Abstract
Private Final
Static
Volatile Constant
Synchronized
Transient
Native
• Public : The Variables and methods can be access any where and any package.
• Protected : The Variables and methods can be access same Class, same Package & sub class.
• Private : The variable and methods can be access in same class only.
Same class - Public, Protected, and Private
Same-package & subclass - Public, Protected
Same Package & non-sub classes - Public, Protected
Different package & Sub classes - Public, Protected
Different package & non- sub classes - Public
Identifiers : are the Variables that are declared under particular Datatype.
Literals: are the values assigned to the Identifiers.
Static : access modifier. Signa: Variable-Static int b; Method- static void meth(int x)
When a member is declared as Static, it can be accessed before any objects of its class are created and without reference to any object. Eg : main(),it must call before any object exit.
Static can be applied to Inner classes, Variables and Methods.
Local variables can’t be declared as static.
A static method can access only static Variables. and they can’t refer to this or super in any way.
Static methods can’t be abstract.
A static method may be called without creating any instance of the class.
Only one instance of static variable will exit any amount of class instances.
Final : access modifier
All the Variables, methods and classes can be declared as Final.
Classes declared as final class can’t be sub classed.
Method ‘s declared as final can’t be over ridden.
If a Variable is declared as final, the value contained in the Variable can’t be changed.
Static final variable must be assigned in to a value in static initialized block.
Transient : access modifier
Transient can be applied only to class level variables.
Local variables can’t be declared as transient.
During serialization, Object’s transient variables are not serialized.
Transient variables may not be final or static. But the complies allows the declaration and no compile time error is generated.
Volatile: access modifier
Volatile applies to only variables.
Volatile can applied to static variables.
Volatile can not be applied to final variables.
Transient and volatile can not come together.
Volatile is used in multi-processor environments.
Native : access modifier
Native applies to only to methods.
Native can be applied to static methods also.
Native methods can not be abstract.
Native methods can throw exceptions.
Native method is like an abstract method. The implementation of the abstract class and native method exist some where else, other than the class in which the method is declared.
Synchronized : access modifier
Synchronized keyword can be applied to methods or parts of the methods only.
Synchronize keyword is used to control the access to critical code in multi-threaded programming.
Declaration of access specifier and access modifiers :
Class - Public, Abstract, Final
Inner Class - Public, Protected, Private, Final, Static,
Anonymous - Public, Protected, Private, Static
Variable - Public, Protected, Private, Final, Static, Transient, Volatile, Native
Method - Public, Protected, Private, Final, Abstract, Static, Native, Synchronized
Constructor - Public, Protected, Private
Free-floating code block - Static, Synchronized
Package : A Package is a collection of Classes Interfaces that provides a high-level layer of access protection and name space management.
Finalize( ) method:
All the objects have Finalize() method, this method is inherited from the Object class.
Finalize() is used to release the system resources other than memory(such as file handles& network connec’s.
Finalize( ) is used just before an object is destroyed and can be called prior to garbage collection.
Finalize() is called only once for an Object. If any exception is thrown in the finalize() the object is still eligible for garbage collection.
Finalize() can be called explicitly. And can be overloaded, but only original method will be called by Ga-collect.
Finalize( ) may only be invoked once by the Garbage Collector when the Object is unreachable.
The signature finalize( ) : protected void finalize() throws Throwable { }
Constructor( ) :
A constructor method is special kind of method that determines how an object is initialized when created.
Constructor has the same name as class name.
Constructor does not have return type.
Constructor cannot be over ridden and can be over loaded.
Default constructor is automatically generated by compiler if class does not have once.
If explicit constructor is there in the class the default constructor is not generated.
If a sub class has a default constructor and super class has explicit constructor the code will not compile.
Object : Object is a Super class for all the classes. The methods in Object class as follows.
Object clone( ) final void notify( ) Int hashCode( )
Boolean equals( ) final void notifyAll( )
Void finalize( ) String toString( )
Final Class getClass( ) final void wait( )
Class : The Class class is used to represent the classes and interfaces that are loaded by the JAVA Program.
Character : A class whose instances can hold a single character value. This class also defines handy methods that can manipulate or inspect single-character data.
constructors and methods provided by the Character class:
Character(char) : The Character class's only constructor, which creates a Character object containing the value provided by the argument. Once a Character object has been created, the value it contains cannot be changed.
compareTo(Character) :An instance method that compares the values held by two character objects.
equals(Object) : An instance method that compares the value held by the current object with the value held by another.
toString() : An instance method that converts the object to a string.
charValue() :An instance method that returns the value held by the character object as a primitive char value.
isUpperCase(char) : A class method that determines whether a primitive char value is uppercase.
String: String is Immutable and String Is a final class. The String class provides for strings whose value will not change.
One accessor method that you can use with both strings and string buffers is the length() method, which returns the number of characters contained in the string or the string buffer. The methods in String Class:-
toString( ) equals( ) indexOff( ) LowerCase( )
charAt( ) compareTo( ) lastIndexOff( ) UpperCase( )
getChars( ) subString( ) trim( )
getBytes( ) concat( ) valueOf( )
toCharArray( ) replace( )
ValueOf( ) : converts data from its internal formate into human readable formate.
String Buffer : Is Mutable , The StringBuffer class provides for strings that will be modified; you use string buffers when you know that the value of the character data will change.
In addition to length, the StringBuffer class has a method called capacity, which returns the amount of space allocated for the string buffer rather than the amount of space used.
The methods in StringBuffer Class:-
length( ) append( ) replace( ) charAt( ) and setCharAt( )
capacity( ) insert( ) substring( ) getChars( )
ensureCapacity( ) reverse( )
setLength( ) delete( )
Wraper Classes : are the classes that allow primitive types to be accessed as Objects.
These classes are similar to primitive data types but starting with capital letter.
Number Byte Boolean
Double Short Character
Float Integer
Long
primitive Datatypes in Java :
According to Java in a Nutshell, 5th ed boolean, byte, char, short, long float, double, int.
Float class : The Float and Double provides the methods isInfinite( ) and isNaN( ).
isInfinite( ) : returns true if the value being tested is infinetly large or small.
isNaN( ) : returns true if the value being tested is not a number.
Character class : defines forDigit( ) digit( ) .
ForDigit( ) : returns the digit character associated with the value of num.
digit( ) : returns the integer value associated with the specified character (which is presumably) according to the specified radix.
String Tokenizer : provide parsing process in which it identifies the delimiters provided by the user, by default delimiters are spaces, tab, new line etc., and separates them from the tokens. Tokens are those which are separated by delimiters.
Observable Class: Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update( ) method of each of its observers to notify the observers that it has changed state.
Observer interface : is implemented by objects that observe Observable objects.
Instanceof( ) :is used to check to see if an object can be cast into a specified type with out throwing a cast class exception.
IsInstanceof( ) : determines if the specified Object is assignment-compatible with the object represented by this class. This method is dynamic equivalent of the Java language instanceof operator. The method returns true if the specified Object argument is non-null and can be cast to the reference type represented by this Class object without raising a ClassCastException. It returns false otherwise.
Garbage Collection : When an object is no longer referred to by any variable, java automatically reclaims memory used by that object. This is known as garbage collection.
System.gc() method may be used to call it explicitly and does not force the garbage collection but only suggests that the JVM may make an effort to do the Garbage Collection.
• this() : can be used to invoke a constructor of the same class.
• super() :can be used to invoke a super class constructor.
Inner class : classes defined in other classes, including those defined in methods are called inner classes. An inner class can have any accessibility including private.
Anonymous class : Anonymous class is a class defined inside a method without a name and is instantiated and declared in the same place and cannot have explicit constructors.
What is reflection API? How are they implemented
Reflection package is used mainlyfor the purpose of getting the class name. by using the getName method we can get name of the class for particular application. Reflection is a feature of the Java programming language. It allows an executing Java program to examine or "introspect" upon itself, and manipulate internal properties of the program.
What is heap in Java
JAVA is fully Object oriented language. It has two phases first one is Compilation phase and second one is interpratation phase. The Compilation phase convert the java file to class file (byte code is only readable format of JVM) than Intepratation phase interorate the class file line by line and give the proper result.
main( ) : is the method where Java application Begins.
String args[ ] : receives any command line argument during runtime.
System : is a predefined Class that provides access to the System.
Out : is output stream connected to console.
Println :displays the output.
Downcasting : is the casting from a general to a more specific type, i.e casting down the hierarchy. Doing a cast from a base class to more specific Class, the cast does;t convert the Object, just asserts it actually is a more specific extended Object.
Upcasting : byte can take Integer values.
Exception
Exception handling
Exception can be generated by Java-runtime system or they can be manually generated by code.
Error-Handling becomes a necessary while developing an application to account for exceptional situations that may occur during the program execution, such as
Run out of memory
Resource allocation Error
Inability to find a file
Problems in Network connectivity.
If the Resource file is not present in the disk, you can use the Exception handling mechanisim to handle such abrupt termination of program.
Exception class : is used for the exceptional conditions that are trapped by the program.
An exception is an abnormal condition or error that occur during the execution of the program.
Error : the error class defines the conditions that do not occur under normal conditions.
Eg: Run out of memory, Stack overflow error.
Java.lang.Object
+….Java.Lang.Throwable Throwable
+…. Java.lang.Error
| +…. A whole bunch of errors
| Exception Error
+….Java.Lang.Exception (Unchecked, Checked)
+….Java.Lang.RuntimeException
| +…. Various Unchecked Exception
|
+…. Various checked Exceptions.
Two types of exceptions:
1. Checked Exceptions : must be declare in the method declaration or caught in a catch block.
Checked exception must be handled at Compile Time. Environmental error that cannot necessarly be detected by Testing, Eg: disk full, brocken Socket, Database unavailable etc.
2. Un-checked Exceptions: Run-time Exceptions and Error, does’t have to be declare.(but can be caught).
Run-time Exceptions : programming errors that should be detectd in Testing ,
Arithmetic, Null pointer, ArrayIndexOutofBounds, ArrayStore, FilenotFound, NumberFormate, IO, OutofMemory.
Errors: Virtual mechine error – class not found , out of memory, no such method , illegal access to private field , etc.
Java Exception handling can be managed by five keywords:
Try : The try block governs the statements that are enclosed within it and defines the scope of exception handler associated with it. Try block follows catch or finally or both.
Catch: This is a default exception handler. since the exception class is the base class for all the exception class, this handler id capable of catching any type of exception.
The catch statement takes an Object of exception class as a parameter, if an exception is thrown the statement in the catch block is executed. The catch block is restricted to the statements in the proceeding try block only.
Try {
// statements that may cause exception
}
catch(Exception obj)
{
}
Finally : when an exception is raised, the statement in the try block is ignored, some times it is necessary to process certain statements irrespective of wheather an exception is raised or not, the finally block is used for this purpose.
Throw : The throw class is used to call exception explicitly. You may want to throw an exception when the user enters a wrong login ID and pass word, you can use throw statement to do so.
The throw statement takes an single argument, which is an Object of exception class.
Throw
If the Object does not belong to a valid exception class the compiler gives error.
Throws :The throws statement species the list of exception that has thrown by a method.
If a method is capable of raising an exception that is does not handle, it must specify the exception has to be handle by the calling method, this is done by using the throw statement.
[
Eg: public void accept password( ) throws illegalException
{
System.out.println(“Intruder”);
Throw new illegalAccesException;
}
Multi Programming
A multithreaded program contains two or more parts that can run concurrently, Each part a program is called thread and each part that defines a separate path of execution.
Thus multithreading is a specified from of multitasking .
There are two distinct types of multitasking .
Process: A Process is , in essence , a program that is executing.
Process-based :is heavy weight- allows you run two or more programs concurrently.
Eg: you can use JAVA compiler at the same time you are using text editor.
Here a program is a small unit of code that can be dispatched by scheduler .
Thread-based: is Light weight- A Program can perform two or more tasks simultaneously.
Creating a thread:
Eg: A text editor can formate at the same time you can print, as long as these two tasks are being perform separate threads.
Thread: can be defined as single sequential flow of control with in a program.
Single Thread : Application can perform only one task at a time.
Multithreaded : A process having more than one thread is said to be multithreaded.
The multiple threads in the process run at the same time, perform different task and interact with each other.
Daemon Thread : Is a low priority thread which runs immedeatly on the back ground doing the Garbage Collection operation for the Java Run time System.
SetDaemon( ) – is used to create DaemonThread.
Creating a Thread :
1. By implementing the Runnable Interface.
2. By extending the thread Class.
Thread Class : Java.lang.Threadclass is used to construct and access the individual threads in a multithreaded application.
Syntax: Public Class
The Thread class define several methods .
o Getname() – obtain a thread name.
o GetPriority() – obtain thread priority.
o Start( ) - start a thread by calling a Run( ).
o Run( ) - Entry point for the thread.
o Sleep( ) - suspend a thread for a period of time.
o IsAlive( ) - Determine if a thread is still running.
o Join( ) - wait for a thread to terminate.
Runable Interface : The Runnable interface consist of a Single method Run( ), which is executed when the thread is activated.
When a program need it inherit from another class besides the thread Class, you need to implement the Runnable interface.
Syntax: public void
Eg: public Class myapplet extends Japplet implements Runnable
{
// Implement the Class
}
* Runnable interface is the most advantageous method to create threads because we need not extend thread Class here.
Life Cycle of Thread :
New Thread -- ---- Not Runnable
----
Dead The Run( ) terminates .
New Thread : When an instance of a thread class is created, a thread enters the new thread state. Thread newThread = new Thread(this);
You have to invoke the Start( ) to start the thread. ie, newThread.Start( );
Runnable : when the Start( ) of the thread is invoked the thread enters into the Runnable State.
Not Runnable : A thread is said to be not runnable state if it
Is Slleping
Is Waiting
Is being blocked by another thread.
sleep(long t); where t= no: of milliseconds for which the thread is inactive.
The sleep( ) is a static method because it operates on the current thread.
Dead : A thread can either die natuarally or be killed.
- A thread dies a natural death when the loop in the Run( ) is complete.
- Assigning null to the thread Object kills the thread.
- If the loop in the Run( ) has a hundred iterations , the life of the thread is a hundred iterators of the loop.
IsAlive( ) : of the thread class is used to determine wheather a thread has been started or stopped. If isAlive( ) returns true the thread is still running otherwise running completed.
Thread Priorities : are used by the thread scheduler to decide when each thread should ne allowed to run.To set a thread priority, use te setpriority( ), which is a member of a thread.
final void setpriority(int level) - here level specifies the new priority seting for the calling thread.
The value level must be with in the range :-
MIN_PRIORITY = 1
NORM_PRIORITY = 5
MAX_PRIORITY = 10
You can obtain the current priority setting by calling getpriority( ) of thread.
final int getpriority( )
Synchronization :
Two ro more threads trying to access the same method at the same point of time leads to synchronization. If that method is declared as Synchronized , only one thread can access it at a time. Another thread can access that method only if the first thread’s task is completed.
Synchronized statement : Synchronized statements are similar to Synchronized method.
A Synchronized statements can only be executed after a thread has acquired a lock for the object or Class reffered in the Synchronized statements.
The general form is - Synchronized(object) {
// statements to be Synchronized
}
Inter Thread Communication : To Avoid pooling , Java includes an elegant interprocess communication mechanisim.
Wait( ) - tells the calling thread to give up the monitor and go to sleep until some other thread enters the same monitor & call notify( ).
notify( ) - wake up the first thread that called wait( ) on the same Object.
notifyall( ) – wake up all the threads that called wait( ) on the same Object.
The highest priority thread aill run fast.
Serialization : The process of writing the state of Object to a byte stream to transfer over the network is known as Serialization.
Deserialization : and restored these Objects by deserialization.
Externalizable : is an interface that extends Serializable interface and sends data into streams in compressed format. It has two methods
WriteExternal(Objectoutput out)
ReadExternal(objectInput in)
I/O Package Java.io.*;
There are two classifications.
• ByteStream - console input
• CharacterStream – File
1. ByteStream : Console Input
Read( ) - one character
Readline( ) – one String
BufferReader br = new BufferReader(new InputStreamReader(System.in));
2. CharacterStream : File
FileInputStream - Store the contents to the File.
FileOutStream - Get the contents from File.
PrintWrite pw = new printwriter(System.out.true);
Pw.println(“ “);
Eg :-
Class myadd
{
public static void main(String args[ ])
{
BufferReader br = new BufferReader(new InputStreamReader(System.in));
System.out.println(“Enter A no : “);
int a = Integer.parseInt(br.Read( ));
System.out.println(“Enter B no : “);
int b = Integer.parseInt(br.Read( ));
System.out.println(“The Addition is : “ (a+b));
}
}
Collections
Collections : A collection allows a group of objects to be treated as a single unit. collection define a set of core Interfaces as follows.
Collection Map Hash Map class
Hash Table class
Set Hash set List
Array List
Sorted set Tree set Vector List
Linked List Sorted map Tree Map class
Collection Interface :
The CI is the root of collection hierarchy and is used for common functionality across all collections. There is no direct implementation of Collection Interface.
Set Interface: extends Collection Interface. The Class Hash set implements Set Interface.
Is used to represent the group of unique elements.
Set stores elements in an unordered way but does not contain duplicate elements.
Sorted set : extends Set Interface. The class Tree Set implements Sorted set Interface.
It provides the extra functionality of keeping the elements sorted.
It represents the collection consisting of Unique, sorted elements in ascending order.
List : extends Collection Interface. The classes Array List, Vector List & Linked List implements List Interface.
Represents the sequence of numbers in a fixed order.
But may contain duplicate elements.
Elements can be inserted or retrieved by their position in the List using Zero based index.
List stores elements in an ordered way.
Map Interface:basic Interface.The classesHash Map & Hash Table implements Map interface.
Used to represent the mapping of unique keys to values.
By using the key value we can retrive the values. Two basic operations are get( ) & put( ) .
Sorted Map : extends Map Interface. The Class Tree Map implements Sorted Map Interface.
Maintain the values of key order.
The entries are maintained in ascending order.
Collection classes:
Abstract Collection
Abstract List Abstract Set Abstract Map
Abstract Array List Hash Set Tree Set Hash Map Tree Map
Sequential
List
Linked List
List Map
| |
Abstract List Dictonary
| |
Vector HashTable
| |
Stack Properities
HashSet : Implements Set Interface. HashSet hs=new HashSet( );
The elements are not stored in sorted order. hs.add(“m”);
TreeSet : Implements Sorted set Interface. TreeSet ts=new TreeSet( );
The elements are stored in sorted ascending order. ts.add(“H”);
Access and retrieval times are quit fast, when storing a large amount of data.
Vector : Implements List Interface.
Vector implements dynamic array. Vector v = new vector( );
Vector is a growable object. V1.addElement(new Integer(1));
Vector is Synchronized, it can’t allow special characters and null values.
All vector starts with intial capacity, after it is reached next time if we want to store object in vector, the vector automatically allocates space for that Object plus extra room for additional Objects.
ArrayList : Implements List Interface.
Array can dynamically increase or decrease size. ArrayList a1=new ArrayList( );
Array List are ment for Random ascessing. A1.add(“a”);
Array List are created with intial size, when the size is increased, the collection is automatically enlarged. When an Objects are removed, the array may be shrunk.
Linked List : Implements List Interface.
Inserting or removing elements in the middle of the array. LinkedList l1=new LinkedList( );
Linked list are meant for Sequential accessing. L1.add(“R”);
Stores Objects in a separate link.
Map Classes: Abstract Map; Hash Map ; Tree Map
Hash Map : Implements Map Interface. Hashmap() , Hashmap(Map m), Hashmap(int capacity)
The Elements may not in Order.
Hash Map is not synchronized and permits null values
Hash Map is not serialized. Hashmap hm = new HashMap( );
Hash Map supports Iterators. hm.put(“Hari”,new Double(11.9));
Hash Table : Implements Map Interface.
Hash Table is synchronized and does not permit null values.
Hash Table is Serialized. Hashtable ht = new Hashtable( );
Stores key/value pairs in Hash Table. ht.put(“Prasadi”,new Double(74.6));
A Hash Table stores information by using a mechanism called hashing. In hashing the informational content of a key is used to determine a unique value, called its Hash Code. The Hash Code is then used as the index at which the data associated with the key is stored. The Transformation of the key into its Hash Code is performed automatically- we never see the Hash Code. Also the code can’t directly index into h c.
Tree Map : Implements Sorted Set Interface. TreeMap tm=new TreeMap( );
The elements are stored in sorted ascending order. tm.put( “Prasad”,new Double(74.6));
Using key value we can retrieve the data.
Provides an efficient means of storing key/value pairs in sorted order and allows rapid retrivals.
Iterator: Each of collection class provided an iterator( ).
By using this iterator Object, we can access each element in the collection – one at a time.
We can remove() ; Hashnext( ) – go next; if it returns false –end of list.
Iterarator Enumerator
Iterator itr = a1.iterator( ); Enumerator vEnum = v.element( );
While(itr.hashNext( )) System.out.println(“Elements in Vector :”);
{ while(vEnum.hasMoreElements( ) )
Object element = itr.next( ); System.out.println(vEnum.nextElement( ) + “ “);
System.out.println(element + “ “);
}
Collections
1.Introduction
2.Legacy Collections
1. The Enumeration Interface
2. Vector
3. Stack
4. Hashtable
5. Properties
3.Java 2 Collections
1. The Interfaces of the collections framework
2. Classes in the collections framework
3. ArrayList & HashSet
4. TreeSet & Maps
Introduction :
•Does your class need a way to easily search through thousands of items quickly?
• Does it need an ordered sequence of elements and the ability to rapidly insert and remove elements in the middle of the sequence?• Does it need an array like structure with random-access ability that can grow at runtime?
List Map
| |
Abstract List Dictonary
| |
Vector HashTable
| |
Stack Properities
The Enumeration Interface :
•enumerate (obtain one at a time) the elements in a collection of objects.
specifies two methods :
boolean hasMoreElements() : Returns true when there are still more elements to extract, and false when all of the elements have been enumerated.
Object nextElement() : Returns the next object in the enumeration as a generic Object reference.
VECTOR :
Vector implements dynamic array. Vector v = new vector( );
Vector is a growable object. V1.addElement(new Integer(1));
Vector is Synchronized, it can’t allow special characters and null values.
Vector is a variable-length array of object references.
Vectors are created with an initial size.
When this size is exceeded, the vector is automatically enlarged.
When objects are removed, the vector may be shrunk.
Constructors : Vector() : Default constructor with initial size 10.
Vector(int size) : Vector whose initial capacity is specified by size.
Vector(int size,int incr) :Vector whose initialize capacity is specified by size and whose increment is specified by incr.
Methods :
final void addElement(Object element) : The object specified by element is added to the vector.
final Object elementAt(int index) : Returns the element at the location specified by index.
final boolean removeElement(Object element) : Removes element from the vector
final boolean isEmpty() : Returns true if the vector is empty, false otherwise.
final int size() : Returns the number of elements currently in the vector.
final boolean contains(Object element) : Returns true if element is contained by the vector and false if it is not.
STACK :
•Stack is a subclass of Vector that implements a standard last-in, first-out stack
Constructor : Stack() Creates an empty stack.
Methods :
Object push(Object item) : Pushes an item onto the top of this stack.
Object pop() : Removes the object at the top of this stack and returns that object as the value of this function. An EmptyStackException is thrown if it is called on empty stack.
boolean empty() : Tests if this stack is empty.
Object peek() : Looks at the object at the top of this stack without removing it from the stack.
int search(Object o) : Determine if an object exists on the stack and returns the number of pops that would be required to bring it to the top of the stack.
HashTable :
Hash Table is synchronized and does not permit null values.
Hash Table is Serialized. Hashtable ht = new Hashtable( );
Stores key/value pairs in Hash Table. ht.put(“Prasadi”,new Double(74.6));
Hashtable is a concrete implementation of a Dictionary.
Dictionary is an abstract class that represents a key/value storage repository.
A Hashtable instance can be used store arbitrary objects which are indexed by any other arbitrary object.
A Hashtable stores information using a mechanism called hashing.
When using a Hashtable, you specify an object that is used as a key and the value (data) that you want linked to that key.
Constructors : Hashtable() Hashtable(int size)
Methods :
Object put(Object key,Object value) : Inserts a key and a value into the hashtable.
Object get(Object key) : Returns the object that contains the value associated with key.
boolean contains(Object value) : Returns true if the given value is available in the hashtable. If not, returns false.
boolean containsKey(Object key) : Returns true if the given key is available in the hashtable. If not, returns false.
Enumeration elements() : Returns an enumeration of the values contained in the hashtable.
int size() : Returns the number of entries in the hashtable.
Properties
•Properties is a subclass of Hashtable
• Used to maintain lists of values in which the key is a String and the value is also a String
• Constructors
Properties()
Properties(Properties propDefault) : Creates an object that uses propDefault for its default value.
Methods :
String getProperty(String key) : Returns the value associated with key.
Strng getProperty(String key, String defaultProperty) : Returns the value associated with key. defaultProperty is returned if key is neither in the list nor in the default property list .
Enumeration propertyNames() : Returns an enumeration of the keys. This includes those keys found in the default property list.
The Interfaces in Collections Framework
Collection Map Iterator
Set List SortedMap ListIterator
|
SortedSet
Collection :
A collection allows a group of objects to be treated as a single unit.
The Java collections library forms a framework for collection classes.
The CI is the root of collection hierarchy and is used for common functionality across all collections.
There is no direct implementation of Collection Interface.
Two fundamental interfaces for containers:
• Collection
boolean add(Object element) : Inserts element into a collection
Set Interface: extends Collection Interface. The Class Hash set implements Set Interface.
Is used to represent the group of unique elements.
Set stores elements in an unordered way but does not contain duplicate elements.
identical to Collection interface, but doesn’t accept duplicates.
Sorted set : extends Set Interface. The class Tree Set implements Sorted set Interface.
It provides the extra functionality of keeping the elements sorted.
It represents the collection consisting of Unique, sorted elements in ascending order.
expose the comparison object for sorting.
List Interface :
ordered collection – Elements are added into a particular position.
Represents the sequence of numbers in a fixed order.
But may contain duplicate elements.
Elements can be inserted or retrieved by their position in the List using Zero based index.
List stores elements in an ordered way.
Map Interface: Basic Interface.The classes Hash Map & HashTable implements Map interface.
Used to represent the mapping of unique keys to values.
By using the key value we can retrive the values.
Two basic operations are get( ) & put( ) .
boolean put(Object key, Object value) : Inserts given value into map with key
Object get(Object key) : Reads value for the given key.
Tree Map Class: Implements Sorted Set Interface.
The elements are stored in sorted ascending order.
Using key value we can retrieve the data.
Provides an efficient means of storing key/value pairs in sorted order and allows rapid retrivals.
TreeMap tm=new TreeMap( );
tm.put( “Prasad”,new Double(74.6));
The Classes in Collections Framework
Abstract Collection
Abstract List Abstract Set Abstract Map
Abstract Array List Hash Set Tree Set Hash Map Tree Map
Sequential
List
Linked List
ArrayList
• Similar to Vector: it encapsulates a dynamically reallocated Object[] array
• Why use an ArrayList instead of a Vector?
• All methods of the Vector class are synchronized, It is safe to access a Vector object from two threads.
• ArrayList methods are not synchronized, use ArrayList in case of no synchronization
• Use get and set methods instead of elementAt and setElementAt methods of vector
HashSet
• Implements a set based on a hashtable
• The default constructor constructs a hashtable with 101 buckets and a load factor of 0.75
HashSet(int initialCapacity)
HashSet(int initialCapacity,float loadFactor)
loadFactor is a measure of how full the hashtable is allowed to get before its capacity is automatically increased
• Use Hashset if you don’t care about the ordering of the elements in the collection
TreeSet
• Similar to hash set, with one added improvement
• A tree set is a sorted collection
• Insert elements into the collection in any order, when it is iterated, the values are automatically presented in sorted order
• Maps : Two implementations for maps:
HashMap
hashes the keys
The Elements may not in Order.
Hash Map is not synchronized and permits null values
Hash Map is not serialized.
Hash Map supports Iterators.
TreeMap
• uses a total ordering on the keys to organize them in a search tree
• The hash or comparison function is applied only to the keys
• The values associated with the keys are not hashed or compared.
How are memory leaks possible in Java
If any object variable is still pointing to some object which is of no use, then JVM will not garbage collect that object and object will remain in memory creating memory leak
What are the differences between EJB and Java beans
the main difference is Ejb componenets are distributed which means develop once and run anywhere. java beans are not distributed. which means the beans cannot be shared .
What would happen if you say this = null
this will give a compilation error as follows
cannot assign value to final variable this
Will there be a performance penalty if you make a method synchronized? If so, can you make any design changes to improve the performance
yes.the performance will be down if we use synchronization.
one can minimize the penalty by including garbage collection algorithm, which reduces the cost of collecting large numbers of short- lived objects. and also by using Improved thread synchronization for invoking the synchronized methods.the invoking will be faster.
How would you implement a thread pool
public class ThreadPool extends java.lang.Object implements ThreadPoolInt
This class is an generic implementation of a thread pool, which takes the following input
a) Size of the pool to be constructed
b) Name of the class which implements Runnable (which has a visible default constructor)
and constructs a thread pool with active threads that are waiting for activation. once the threads have finished processing they come back and wait once again in the pool.
This thread pool engine can be locked i.e. if some internal operation is performed on the pool then it is preferable that the thread engine be locked. Locking ensures that no new threads are issued by the engine. However, the currently executing threads are allowed to continue till they come back to the passivePool
How does serialization work
Its like FIFO method (first in first out)
How does garbage collection work
There are several basic strategies for garbage collection: reference counting, mark-sweep, mark-compact, and copying. In addition, some algorithms can do their job incrementally (the entire heap need not be collected at once, resulting in shorter collection pauses), and some can run while the user program runs (concurrent collectors). Others must perform an entire collection at once while the user program is suspended (so-called stop-the-world collectors). Finally, there are hybrid collectors, such as the generational collector employed by the 1.2 and later JDKs, which use different collection algorithms on different areas of the heap
How would you pass a java integer by reference to another function
Passing by reference is impossible in JAVA but Java support the object reference so.
Object is the only way to pass the integer by refrence.
What is the sweep and paint algorithm
The painting algorithm takes as input a source image and a list of brush sizes. sweep algo is that it computes the arrangement of n lines in the plane ... a correct algorithm,
Can a method be static and synchronized
no a static mettod can't be synchronized
Do multiple inheritance in Java
Its not possible directly. That means this feature is not provided by Java, but it can be achieved with the help of Interface. By implementing more than one interface.
What is data encapsulation? What does it buy you
The most common example I can think of is a javabean. Encapsulation may be used by creating 'get' and 'set' methods in a class which are used to access the fields of the object. Typically the fields are made private while the get and set methods are public.
dEncapsulation can be used to validate the data that is to be stored, to do calculations on data that is stored in a field or fields, or for use in introspection (often the case when using javabeans in Struts, for instance).
What is reflection API? How are they implemented
Reflection package is used mainlyfor the purpose of getting the class name. by using the getName method we can get name of the class for particular application .
Reflection is a feature of the Java programming language. It allows an executing Java program to examine or "introspect" upon itself, and manipulate internal properties of the program.
What are the primitive types in Java
According to Java in a Nutshell, 5th ed
boolean, byte, char, short, long float, double, int
Is there a separate stack for each thread in Java
No
What is heap in Java
JAVA is fully Object oriented language. It has two phases first one is Compilation phase and second one is interpratation phase. The Compilation phase convert the java file to class file (byte code is only readable format of JVM) than Intepratation phase interorate the class file line by line and give the proper result.
In Java, how are objects / values passed around
In Java Object are passed by reference and Primitive data is always pass by value
Do primitive types have a class representation
Primitive data type has a wrapper class to present.
Like for int - Integer , for byte Byte, for long Long etc ...
How all can you free memory
With the help of finalize() method.
If a programmer really wants to explicitly request a garbage collection at some point, System.gc() or Runtime.gc() can be invoked, which will fire off a garbage collection at that time.
Does java do reference counting
It is more likely that the JVMs you encounter in the real world will use a tracing algorithm in their garbage-collected heaps
What does a static inner class mean? How is it different from any other static member
A static inner class behaves like any ``outer'' class. It may contain methods and fields.
It is not necessarily the case that an instance of the outer class exists even when we have created an instance of the inner class. Similarly, instantiating the outer class does not create any instances of the inner class.
The methods of a static inner class may access all the members (fields or methods) of the inner class but they can access only static members (fields or methods) of the outer class. Thus, f can access the field x, but it cannot access the field y.
How do you declare constant values in java
Using Final keyword we can declare the constant values How all can you instantiate final members Final member can be instantiate only at the time of declaration. null
How is serialization implemented in Java
A particular class has to implement an Interface java.io.Serializable for implementing serialization. When you have an object passed to a method and when the object is reassigned to a different one, then is the original reference lost No Reference is not lost. Java always passes the object by reference, now two references is pointing to the same object.
What are the different kinds of exceptions? How do you catch a Runtime exception
There are 2 types of exceptions.
1. Checked exception
2. Unchecked exception.
Checked exception is catched at the compile time while unchecked exception is checked at run time.
1.Checked Exceptions : Environmental error that cannot necessarily be detected by testing; e.g. disk full, broken socket, database unavailable, etc.
2. Unchecked exception.
Errors : Virtual machine error: class not found, out of memory, no such method, illegal access to private field, etc.
Runtime Exceptions :Programming errors that should be detected in testing: index out of bounds, null pointer, illegal argument, etc.
Checked exceptions must be handled at compile time. Runtime exceptions do not need to be. Errors often cannot be
What are the differences between JIT and HotSpot
The Hotspot VM is a collection of techniques, the most significant of which is called "adaptive optimization.
The original JVMs interpreted bytecodes one at a time. Second-generation JVMs added a JIT compiler, which compiles each method to native code upon first execution, then executes the native code. Thereafter, whenever the method is called, the native code is executed. The adaptive optimization technique used by Hotspot is a hybrid approach, one that combines bytecode interpretation and run-time compilation to native code.
Hotspot, unlike a regular JIT compiling VM, doesn't do "premature optimization"
What is a memory footprint? How can you specify the lower and upper limits of the RAM used by the JVM? What happens when the JVM needs more memory?
when JVM needs more memory then it does the garbage collection, and sweeps all the memory which is not being used.
What are the disadvantages of reference counting in garbage collection?
An advantage of this scheme is that it can run in small chunks of time closely interwoven with the execution of the program. This characteristic makes it particularly suitable for real-time environments where the program can't be interrupted for very long. A disadvantage of reference counting is that it does not detect cycles. A cycle is two or more objects that refer to one another, for example, a parent object that has a reference to its child object, which has a reference back to its parent. These objects will never have a reference count of zero even though they may be unreachable by the roots of the executing program. Another disadvantage is the overhead of incrementing and decrementing the reference count each time. Because of these disadvantages, reference counting currently is out of favor.
Is it advisable to depend on finalize for all cleanups
The purpose of finalization is to give an opportunity to an unreachable object to perform any clean up before the object is garbage collected, and it is advisable.
can we declare multiple main() methods in multiple classes. ie can we have each main method in its class in our program?
YES
JDBC
How to Interact with DB?
Generally every DB vendor provides a User Interface through which we can easily execute SQL query’s and get the result (For example Oracle Query Manager for Oracle, and TOAD (www.quest.com) tool common to all the databases). And these tools will help DB developers to create database. But as a programmer we want to interact with the DB dynamically to execute some SQL queries from our application (Any application like C, C++, JAVA etc), and for this requirement DB vendors provide some Native Libraries (Vendor Specific) using this we can interact with the DB i.e. If you want to execute some queries on Oracle DB, oracle vendor provides an OCI (Oracle Call Interface) Libraries to perform the same.
About ODBC
What is ODBC
ODBC (Open Database Connectivity) is an ISV (Independent software vendor product) composes of native API to connect to different databases through via a single API called ODBC.
Open Database Connectivity (ODBC) is an SQL oriented application programming interface developed by in collaboration with IBM and some other database vendors.
ODBC comes with Microsoft products and with all databases on Windows OS.
ODBC Architecture
Advantages
• Single API (Protocol) is used to interact with any DB
• Switching from one DB to another is easy
• Doesn’t require any modifications in the Application when you want to shift from one DB to other.
What for JDBC?
As we have studied about ODBC and is advantages and came to know that it provides a common API to interact with any DB which has an ODBC Service Provider’s Implementation written in Native API that can be used in your applications.
If an application wants to interact with the DB then the options which have been explained up to now in this book are:
1. Using Native Libraries given by the DB vendor
2. Using ODBC API
And we have listed there Advantages and Disadvantages.
But if the application is a JAVA application then the above given options are not recommended to be used due to the following reasons
1. Native Libraries given by DB vendor
a. Application becomes vendor dependent and
b. The application has to use JNI to interact with Native Lib which may cause serious problem for Platform Independency in our applications.
2. And the second option given was using ODBC API which can solve the 1.a problem but again this ODBC API is also a Native API, so we have to use JNI in our Java applications which lead to the 1.b described problem.
And the answer for these problems is JDBC (Java Data Base Connectivity) which provides a common Java API to interact with any DB.
What is JDBC
As explained above JDBC standards for Java Data Base Connectivity. It is a specification given by Sun Microsystems and standards followed by X/Open SAG (SQL Access Group) CLI (Call Level Interface) to interact with the DB.
Java programing language methods. The JDBC API provides database-independent connectivity between the JAVA Applications and a wide range of tabular data bases. JDBC technology allows an application component provider to:
• Perform connection and authentication to a database server
• Manage transactions
• Moves SQL statements to a database engine for preprocessing and execution
• Executes stored procedures
• Inspects and modifies the results from SELECT statements
JDBC API
JDBC API is divided into two parts
1. JDBC Core API
2. JDBC Extension or Optional API
JDBC Core API (java.sql package)
This part of API deals with the following futures
1. Establish a connection to a DB
2. Getting DB Details
3. Getting Driver Details
4. maintaining Local Transaction
5. executing query’s
6. getting result’s (ResultSet)
7. preparing pre-compiled SQL query’s and executing
8. executing procedures & functions
JDBC Ext OR Optional API (javax.sql package)
This part of API deals with the following futures
1. Resource Objects with Distributed Transaction Management support
2. Connection Pooling.
These two parts of Specification are the part of J2SE and are inherited into J2EE i.e. this specification API can be used with all the component’s given under J2SE and J2EE.
JDBC Architecture:
In the above show archetecture diagram the JDBC Driver forms an abstraction layer between the JAVA Application and DB, and is implemented by 3rd party vendors or a DB Vendor. But whoever may be the vendor and what ever may be the DB we need not to worry will just us JDCB API to give instructions to JDBC Driver and then it’s the responsibility of JDBC Driver Provider to convert the JDBC Call to the DB Specific Call.
And this 3rd party vendor or DB vendor implemented Drivers are classified into 4-Types namely
Types Of Drivers :
1. Type-1 (JDBC ODBC-Bridge Driver) JDBC-ODBC Bridge Driver
2. Type-2 (Java-Native API Driver) Native API Partly JAVA Driver (Thick Driver)
3. Type-3 (Java Net Protocol Driver) Intermediate DataBase Access Server
4. Type-4 (Java Native Protocol driver) Pure JAVA Driver (Thin driver)
Type-1 : JDBC-ODBC Bridge Driver :
Since ODBC is written in C-language using pointers, so JAVA does’t support pointers, a java program can’t communate directly with the DataBase. The JDBC-ODBC bridge drivertransulates JDBC API calls to ODBC API calls.
Architecture
This type of Driver is designed to convert the JDBC request call to ODBC call and ODBC response call to JDBC call.
The JDBC uses this interface in order to communicate with the database, so neither the database nor the middle tier need to be Java compliant. However ODBC binary code must be installed on each client machine that uses this driver. This bridge driver uses a configured data source.
Advantages
• Simple to use because ODBC drivers comes with DB installation/Microsoft front/back office product installation
• JDBC ODBC Drivers comes with JDK software
Disadvantages
• More number of layers between the application and DB. And more number of API conversions leads to the downfall of the performance.
• Slower than type-2 driver
Where to use?
This type of drivers are generaly used at the development time to test your application’s.
Because of the disadvantages listed above it is not used at production time. But if we are not available with any other type of driver implementations for a DB then we are forced to use this type of driver (for example Microsoft Access).
Examples of this type of drivers
JdbcOdbcDriver from sun
Sun’s JdbcOdbcDriver is one of type-1 drivers and comes along with sun j2sdk (JDK).
Setting environment to use this driver
1. Software
ODBC libraries has to be installed.
2. classpath
No additional classpath settings are required apart from the runtime jar (c:\j2sdk1.4\jre\lib\rt.jar) which is defaultly configured.
3. Path
No additional path configuration is required.
How to use this driver
1. Driver class name sun.jdbc.odbc.JdbcOdbcDriver
2. Driver URL dbc:odbc:
here
Steps to create
1. run ‘Data Sources (ODBC)’ from Control Panal\Administrative Tools\
(for Windows 2000 server/2000 professional/XP)
run ‘ODBC Data Sources’ from Control Panel\
2. click on Add button available on the above displayed screen. this opens a new window titled ‘Create New Data Source’ which displays all the available DB’s lable DB’s ODBC drivers currently installed on your system.
3. Select the suitable driver and click on Finish
4. Give the required info to the driver (like username, service id etc)
Type-2 : Native API Partly JAVA Driver (Thick Driver) :
JDBC Database calls are translated into Vendor-specific API calls. The database will process the request and send the results back through API to JDBC Driver – this will translate the results to the JDBC standard and return them to the Java application.
The Vendor specific language API must be installed on every client that runs the JAVA application.
Architecture
This driver converts the JDBC call given by the Java application to a DB specific native call (i.e. to C or C++) using JNI (Java Native Interface).
Advantages :Faster than the other types of drivers due to native library participation in socket programing.
Disadvantage : DB specifiic native client library has to be installed in the client machine.
• Preferablly work in local network environment because network service name must be configured in client system
Where to use?
This type of drivers are suitable to be used in server side applications.
Not recommended to use with the applications using two tier model (i.e. client and database layer’s) because in this type of model client used to interact with DB using the driver and in such a situation the client system sould have the DB native library.
Examples of this type of drivers
1. OCI 8 (Oracle Call Interface) for Oracle implemented by Oracle Corporation.
Setting environment to use this driver
• Software: Oracle client software has to be installed in client machine
• classpath %ORACLE_HOME%\ora81\jdbc\lib\classes111.zip
• path %ORACLE_HOME%\ora81\bin
How to use this driver
• Driver class name oracle.jdbc.driver.OracleDriver
• Driver URL jdbc:oracle:oci8:@TNSName
Note: TNS Names of Oracle is available in Oracle installed folder %ORACLE_HOME%\Ora81\network\admin\tnsnames.ora
2. Weblogic Jdriver for Oracle implemented by BEA Weblogic:
Setting environment to use this driver
• Oracle client software has to be installed in client machine
• weblogicoic dll’s has to be set in the path
• classpath d:\bea\weblogic700\server\lib\weblogic.jar
• path %ORACLE_HOME%\ora81\bin;
d:\bea\weblogic700\server\bin\
o oci817_8 if you are using Oracle 8.1.x
o oci901_8 for Oracle 9.0.x
o oci920_8 for Oracle 9.2.x
How to use this driver
• Driver class name weblogic.jdbc.oci.Driver
• Driver URL jdbc:weblogic:oracle:HostName
Type-3 Intermediate DataBase Access Server :
Type-3 Driver uses an Intermediate(middleware) database driver that has the ability to connect multiple JAVA clients to multiple database servers.
Client connect to the Databse server via an Intermediate server component (such as listener) that acts as a gateway for multple database servers.
Bea weblogic includes Type-3 Driver.
Architecture :
This type of drivers responsibility is to convert JDBC call to Net protocol (Middleware listener dependent) format and redirect the client request to Middleware Listener and middleware listener inturn uses type-1, type-2 or type-4 driver to interact with DB.
Advantages:
• It allows the flexibility on the architecture of the application.
• In absence of DB vendor supplied driver we can use this driver
• Suitable for Applet clients to connect DB, because it uses Java libraries for communication between client and server.
Disadvantages:
• From client to server communication this driver uses Java libraries, but from server to DB connectivity this driver uses native libraries, hence number of API conversion and layer of interactions increases to perform operations that leads to performance deficit.
• Third party vendor dependent and this driver may not provide suitable driver for all DBs
Where to use?
• Suitable for Applets when connecting to databases
Examples of this type of drivers:
1. IDS Server (Intersolv) driver available for most of the Databases
Setting environment to use this driver
• Software: IDS software required to be downloaded from the following URL
[ http://www.idssoftware.com/idsserver.html -> Export Evaluation ]
• classpath C:\IDSServer\classes\jdk14drv.jar
• path
How to use this driver
• Driver class name ids.sql.IDSDriver
• Driver URL jdbc:ids://localhost:12/conn?dsn='IDSExamples'
Note: DSN Name must be created in ServerDSN
Type-4 Pure JAVA Driver (Thin driver) :
Type-4 Driver translates JDBC-API calls to direct network calls using vendor specific networking protocols by making direct server connections with the database.
Architecture
This type of driver converts the JDBC call to a DB defined native protocol.
Advantage
• Type-4 driver are simple to deploy since there is No client native libraries required to be installed in client machine
• Comes with most of the Databases
Disadvantages:
• Slower in execution compared with other JDBC Driver due to Java libraries are used in socket communication with the DB
Where to use?
• This type of drivers are sutable to be used with server side applications, client side application and Java Applets also.
Examples of this type of drivers
1) Thin driver for Oracle implemented by Oracle Corporation
Setting environment to use this driver
• classpath %ORACLE_HOME%\ora81\jdbc\lib\classes111.zip
How to use this driver
• Driver class name oracle.jdbc.driver.OracleDriver
• Driver URL jdbc:oracle:thin:@HostName:
2) MySQL Jconnector for MySQL database
Setting environment to use this driver
• classpath C:\mysql\mysql-connector-java-3.0.8-stable\mysql-connector-java-3.0.8-stable-bin.jar
How to use this driver
• Driver class name com.mysql.jdbc.Driver
• Driver URL jdbc:mysql:///test
Chapter 3 [JDBC Core API]
In this chapter we are going to discuss about 3 versions of JDBC: JDBC 1.0, 2.0 and 3.0
Q) How JDBC API is common to all the Databases and also to all drivers?
A) Fine! The answer is JDBC API uses Factory Method and Abstract Factory Design pattern implementations to make API common to all the Databases and Drivers. In fact most of the classes available in JDBC API are interfaces, where Driver vendors must provide implementation for the above said interfaces.
Q) Then how JDBC developer can remember or find out the syntaxes of vendor specific classes?
A) No! developer need not have to find out the syntaxes of vendor specific implementations why because DriverManager is one named class available in JDBC API into which if you register Driver class name, URL, user and password, DriverManager class in-turn brings us one Connection object.
Q) Why most of the classes given in JDBC API are interfaces?
A) Why abstract class and abstract methods are?
Abstract class forces all sub classes to implement common methods whichever are required implementations. Only abstract method and class can do this job. That’s’ why most part of the JDBC API is a formation of interfaces.
JDBC API comes in 2 packages
java.sql.*
javax.sql.*
First of all I want to discuss briefly about all the list of interfaces and classes available in java.sql. package
Interfaces index
Driver
Every JDBC Driver vendor must one sub class of this class for initial establishment of Connections. DriverManager class need to be first registered with this class before accepting URL and other information for getting DB connection.
Method index
• Connection connect(String url, Properties info)
This method takes URL argument and user name & password info as Properties object
• boolean acceptURL(String url)
This method returns boolean value true if the given URL is correct, false if any wrong in URL
• boolean jdbcComplaint()
JDBC compliance requires full support for the JDBC API and full support for SQL 92 Entry Level. It is expected that JDBC compliant drivers will be available for all the major commercial databases.
Connection
Connection is class in-turn holds the TCP/IP connection with DB. Functions available in this class are used to manage connection live-ness as long as JDBC application wants to connect with DB. The period for how long the connection exists is called as Session. This class also provides functions to execute various SQL statements on the DB. For instance the operations for DB are mainly divided into 3 types
• DDL (create, alter, and drop)
• DML (insert, select, update and delete)
• DCL (commit, rollback) and also
• call function_name (or) call procedure_name
Method Index
• Statement createStatement()
• PreparedStatement prepareStatement(String preSqlOperation)
• CallableStatement prepareCall(String callToProc())
Statement
Statement class is the super class in its hierarchy. Provides basic functions to execute query (select) and non-related (create, alter, drop, insert, update, delete) query operations.
Method Index
• int executeUpdate(String sql)
This function accepts non-query based SQL operations; the return value int tells that how many number of rows effected/updated by the given SQL operation.
• ResultSet executeQuery(String sql)
This function accepts SQL statement SELECT and returns java buffer object which contains temporary instance of SQL structure maintaining all the records retrieved from the DB. This object exists as long as DB connection exist.
• boolean execute()
This function accepts all SQL operations including SELECT statement also.
PreparedStatement
PreparedStatement class is sub classing from Statement class. While connection class prepareStatement function is creating one new instance this class, function takes one String argument that contains basic syntax of SQL operation represented with “?” for IN parameter representation. In the further stages of the JDBC program, programmer uses setXXX(int index, datatype identifier) to pass values into IN parameter and requests exdcute()/ exuecteUpdate() call.
Method Index
• setInt(int index, int value) – similar functions are provided for all other primitive parameters
• setString(int index, String value)
• setObject(int index, Object value)
• setBinaryStream(int index, InputStream is, int length)
CallableStatement
ResultSet ResultSetMetaData DatabaseMetaData
BLOB CLOB REF
SavePoint Struct
SQLInput SQLOutput SQLData
Class diagram required here
// TypeI DriverTest,java
package com.digitalbook.j2ee.jdbc;
import java.sql.*;
public class TypeIDriverTest
{
Connection con;
Statement stmt;
ResultSet rs;
public TypeIDriverTest ()
{
try {
// Load driver class into default ClassLoader
Class.forName ("sun.jdbc.odbc.JdbcOdbcDriver");
// Obtain a connection with the loaded driver
con =DriverManager.getConnection ("jdbc:odbc:digitalbook","scott","tiger");
URL String - ("
// create a statement
st=con.createStatement();
//execute SQL query
rs =st.executeQuery ("select ename,sal from emp");
System.out.println ("Name Salary");
System.out.println ("--------------------------------");
while(rs.next())
{
System.out.println (rs.getString(1)+" "+rs.getString(2));
}
rs.close ();
stmt.close ();
con.close ();
}
catch(Exception e)
{
e.printStackTrace ();
}
}
public static void main (String args[])
{
TypeIDriverTest demo=new TypeIDriverTest ();
}
}
// TypeIIDriverTest,java
package com.digitalbook.j2ee.jdbc;
import java.sql.*;
public class TypeIIDriverTest
{
Connection con;
Statement stmt;
ResultSet rs;
public TypeIIDriverTest ()
{
try {
// Load driver class into default ClassLoader
Class.forName ("oracle.jdbc.driver.OracleDriver");
// Obtain a connection with the loaded driver
con =DriverManager.getConnection ("jdbc:oracle:oci8:@digital","scott","tiger");
// create a statement
st=con.createStatement();
//execute SQL query
rs =st.executeQuery ("select ename,sal from emp");
System.out.println ("Name Salary");
System.out.println ("--------------------------------");
while(rs.next())
{
System.out.println (rs.getString(1)+" "+rs.getString(2));
}
rs.close ();
stmt.close ();
con.close ();
}
catch(Exception e)
{
e.printStackTrace ();
}
}
public static void main (String args[])
{
TypeIIDriverTest demo=new TypeIIDriverTest ();
}
}
Chapter 9 : [javax.sql package]
This package supplements the java.sql package and is included as a part of JDK 1.4 version. This package mainly provides following features:
1. DataSource interface was introduced in substitution to DriverManager class for getting connection objects.
2. Connection Pooling
3. Distributed TX management
4. RowSets
Applications can directly use DataSource and RowSet API but connection pooling and Distributed TX management APIs are used internally by the middle-tier infrastructure.
DataSource
DataSource is an interface. Driver vendor will provide implementation for this interface (That means in case JDBC Driver Type II driver Oracle vendor for Oracle DB, Intersolv in case of IDSServer). This object is used to obtain connections into any type of JDBC program. Though DriverManager class is ideal for getting DB connection object, this class provides some extra features over DriverManager class:
• Applications will obtain DB connection objects through via this factory class
• DataSource object will be registered into JNDI, hence any application connected in the network can obtain this object by requesting JNDI API, DataSource class is having one method called getConnection() geives one Connection object
• Application do not need to hard code a driver class
• Changes can be made to a data source properties, which means that it is not necessary to make changes in application code when something about the data source or driver changes
• Connection pooling and Distributed transactions are available through only the connection obtained from this object. Connection obtained through DriverManager class do not have this capability
DataSource interface is implemented by driver vendor. There are 3 types of implementations available:
1. Basic Implementation- Produces a standard connection object.
2. Connection Pooling Implementation- Produces a connection object that automatically participates in connection pooling. This implementation works with a middle-tier connection pooling manager.
3. Distributed transaction implementation- Produces a connection object that may be used for distributed transactions and almost always participates in connection pooling. This implementation works with a middle-tier transaction manager and almost always with a connection pool manager.
A driver that is accessed via a DataSource object does not register itself with the DriverManager. Rather, a DataSource object is retrieved though a lookup operation and then used to create a Connection object. With a basic implementation, the connection obtained through a DataSource object is identical to a connection obtained through the DriverManager facility.
Method Index
• Connection getConnection() – This function returns Connection object on demand of this method.
• Connection getConnection(String user, String pass) – This function returns Connection object on demand of this method by passing username and password.
Sub classes of this interface are
Type III Driver – IDSServer – Intersolv – ids.jdbc.IDSDataSource
Type III Driver – WebLogic – BEA – weblogic.jdbc.jta.DataSource – XA Support
Connection Pooling
Connections made via a DataSource object that is implemented to work with a middle tier connection pool manager will participate in connection pooling. This can improve the performance dramatically because creating a new connection is very expensive.
Connection Pool provides following features:
• Substantial improvement in the performance of DB application can be accomplished by pre-caching the DB connection objects
• CPM supplied DB connections are remote enable
• CPM supplied DB connections are cluster aware
• CPM supplied DB connections supports DTM (distributed TXs)
• CPM supplied DB connections are not actual DB Connection objects, in turn they are remote object, hence even though client closes DB connection using con.close() the actual connection may not be closed instead RMI connection between client to CPM are closed
• CPM supplied DB connection objects are serializable, hence client from any where in the network can access DB connections
The classes and interfaces used for connection pooling are:
1. ConnectionPoolDataSource
2. PooledConnection
3. ConnectionEvent
4. ConnectionEventListener
Connection Pool Manager resided on middle tier system uses these classes and interfaces behind the scenes. When the ConnectionPooledDataSource object is called on to create PooledConnection object, the connection pool manager will register as a ConnectionEventListener object with the new PooledConnection object. When the connection is closed or there is an error, the connection pool manager (being listener) gets a notification that includes a ConnectionEvent object.
Distributed Transactions
As with pooled connections, connections made via data source object that is implemented to work with the middle tier infrastructure may participate in distributed transactions. This gives an application the ability to involve data sources on multiple servers in a single transaction.
The classes and interfaces used for distributed transactions are:
• XADataSource
• XAConnection
These interfaces are used by transaction manager; an application does not use them directly.
The XAConnection interface is derived from the PooledConnection interface, so what applies to a pooled connection also applies to a connection that is part of distributed transaction. A transaction manager in the middle tier handles everything transparently. The only change in application code is that an application cannot do anything that would interfere with the transaction manager’s handling of the transaction. Specifically application cannot call the methods Connection.commit or Connection.rollback and it cannot set the connection to be in auto-commit mode.
An application does not need to do anything special to participate in a distributed transaction. It simply creates connections to the data sources it wants to use via the DataSource.getConnection method, just as it normally does. The transaction manager manages the transaction behind the scenes. The XADataSource interface creates XAConnection objects, and each XAConnection object creates an XAResource object that the transaction manager uses to manage the connection.
Rowsets
The RowSet interface works with various other classes and interfaces behind the scenes. These can be grouped into three categories.
1. Event Notification
o RowSetListener
A RowSet object is a JavaBeansTM component because it has properties and participates in the JavaBeans event notification mechanism. The RowSetListener interface is implemented by a component that wants to be notified about events that occur to a particular RowSet object. Such a component registers itself as a listener with a rowset via the RowSet.addRowSetListener method.
o When the RowSet object changes one of its rows, changes all of it rows, or moves its cursor, it also notifies each listener that is registered with it. The listener reacts by carrying out its implementation of the notification method called on it.
o RowSetEvent
As part of its internal notification process, a RowSet object creates an instance of RowSetEvent and passes it to the listener. The listener can use this RowSetEvent object to find out which rowset had the event.
2. Metadata
RowSetMetaData
This interface, derived from the ResultSetMetaData interface, provides information about the columns in a RowSet object. An application can use RowSetMetaData methods to find out how many columns the rowset contains and what kind of data each column can contain.
The RowSetMetaData interface provides methods for setting the information about columns, but an application would not normally use these methods. When an application calls the RowSet method execute, the RowSet object will contain a new set of rows, and its RowSetMetaData object will have been internally updated to contain information about the new columns.
3. The Reader/Writer Facility
A RowSet object that implements the RowSetInternal interface can call on the RowSetReader object associated with it to populate itself with data. It can also call on the RowSetWriter object associated with it to write any changes to its rows back to the data source from which it originally got the rows. A rowset that remains connected to its data source does not need to use a reader and writer because it can simply operate on the data source directly.
RowSetInternal
By implementing the RowSetInternal interface, a RowSet object gets access to its internal state and is able to call on its reader and writer. A rowset keeps track of the values in its current rows and of the values that immediately preceded the current ones, referred to as the original values. A rowset also keeps track of (1) the parameters that have been set for its command and (2) the connection that was passed to it, if any. A rowset uses the RowSetInternal methods behind the scenes to get access to this information. An application does not normally invoke these methods directly.
RowSetReader
A disconnected RowSet object that has implemented the RowSetInternal interface can call on its reader (the RowSetReader object associated with it) to populate it with data. When an application calls the RowSet.execute method, that method calls on the rowset's reader to do much of the work. Implementations can vary widely, but generally a reader makes a connection to the data source, reads data from the data source and populates the rowset with it, and closes the connection. A reader may also update the RowSetMetaData object for its rowset. The rowset's internal state is also updated, either by the reader or directly by the method RowSet.execute.
RowSetWriter
A disconnected RowSet object that has implemented the RowSetInternal interface can call on its writer (the RowSetWriter object associated with it) to write changes back to the underlying data source. Implementations may vary widely, but generally, a writer will do the following:
Make a connection to the data source
Check to see whether there is a conflict, that is, whether a value that has been changed in the rowset has also been changed in the data source
Write the new values to the data source if there is no conflict
Close the connection
The RowSet interface may be implemented in any number of ways, and anyone may write an implementation. Developers are encouraged to use their imaginations in coming up with new ways to use rowsets.
Type III Driver – WebLogic – BEA – weblogic.jdbc.common.internal.ConnectionPool
Type III Driver – WebLogic – BEA – weblogic.jdbc.connector.internal.ConnectionPool
Type II & IV driver – Oracle DB - Oracle –
JDBC:
There are three types of statements in JDBC
Create statement : Is used to execute single SQL statements.
Prepared statement: Is used for executing parameterized quaries. Is used to run pre-compiled SEQL Statement.
Callable statement: Is used to execute stored procedures.
Stored Procedures: Is a group of SQL statements that perform a logical unit and performs a particular task.
Are used to encapsulate a set operations or queries t execute on data.
execute() – returns Boolean value
executeupdate( ) – returns resultset Object
executeupdate( ) – returns integer value
Loading the Driver:
Class.forName(“sun.jdbc.odbc.JdbcOdbcDriver”);
Conn=DriverManager.getConnection(“jdbc:odbc:dsn”, “username”, “password”);
( ORACLE Driver )
Class.forName(“Oracle.jdbc.driver.OracleDriver”);
Conn=DriverManager.getConnection(“jdbc:oracle:thin:@192.168.1.105:1521:dbn”, “username”, “password”);
Data base connection:
Public static void main(String args[]);
Connection con;
Statement st;
Resultset rs;
try { // Getting all rows from Table
Clas.forName(“sun.jdbc.odbc.jdbcodbc”);
Conn=DriverManager.getConnction(“jdbc.odbc.dsn”, “username” , ”password”);
st = con.createstatement( );
rs = st.executestatement(“SELECT * FROM mytable”);
while(rs.next());
{
String s= rs.getString(1); or rs.setString(“COL_A”);
int i = rs. getInt(2);
Float f = rs.getfloat(3);
Process(s,i,f);
}
catch(SQLException e)
{ }
//Getting particular rows from Table
st = con.createstatement( );
rs = st.executequery(“SELECT * FROM mytable WHERE COL A = “Prasad”);
while(rs.next( ));
{
String s = rs.getString(1);
Int i = rs.getint(2);
Float f = rs.getfloat(3);
Process(s,i,f);
}
Catch(SQLException e); { }
//updating a row from table.
try {
st = con.createstatement( );
int numupdated = st.executeupdate(“UPDATE mytable SET COL_A = “prasad” WHERE COL_B=”746”);
rs = st.executeupdate();
conn.close(); }
catch(SQLExceptione); { }
// Receiving rows from table
try {
st = con.preparedstatement( );
rs = st.execurtestatement(“SELECT * FROM mytable SET COL_A=?’);
int colunm=1;
rs.setString(colunm,”hari”);
rs = st.executeQuery( );
//update rwo from table
st = con.createstatement( );
int numupdated = st.executeupdate(“UPDATE mytable SET COL_A =? WHERE COL_B=?”);
int column=1;
rs.setString(colunm,”Prasad”);
int column=2;
rs.setString(column,”746”);
int numupdated = st.executeupdate( );
} catch(SqlException e); { }
//callable statement
try {
cst = con.preparecall(“{call add1(??,??)}”);
cst.setint(1,a);
cst.setint(2,b);
cst.registerOurPrameter(1,Types.INTEGER);
cst.executeQuery( );
System.out.println(“rs.getString( )”); }
Connection Pool with webLogic server :
You can connect the database in your app using :
Class.forName(“weblogic.jdbc.oci.Driver”).newInstance();
Java.sql.Connection conn = Driver.connect(“jdbc:weblogic:Oracle:dbn”, ”username”, “password”);
( Or )
java.util.Properties prop = new java.util.Properties( );
prop.put(“user”, “hari”);
prop.put(“password”,”prasad”);
java.sql.Driver d = (java.sql.Driver)Class.forName(“weblogic.jdbc.oci.Driver”).newInstance( );
java.sql.Connection conn = d.connect(“jdbc:weblogic:Oracle:dbn”, prop);
public static void main(String args[]) throws Exception
{
java.sql.Connection con=null;
java.sql.satement st =null;
try {
context ctx=null;
Hashtable ht = new Hashtable( );
ht.put(Context.INTIAL_CONTEXT_FACTORY,”weblogic:jndi:WLInitialContextFACTORY”);
ht.put(Context_PROVIDER_URL,”t3://Localhost:7001”);
//get a context from JNDI lookup
ctx = newIntialContext( ):
java.sql.Datasourse ds =(java.sql.DataSource)ctx.lookup(“OraclegbJNDI”);
con =ds.getConnection( );
System.out.Println(“Making Connection……”);
st = conn.createstatement( );
}
finally {
try {
if(stmt !=null)
stmt.close( );
if(stmt !=null)
con.close( ); }
What is a transaction
transaction is collection of logical operation that perform a task
Transaction should ACID properties.
A for Automicity
C for Consistency
I for Isolation
D for Durability.
A transaction can be termed as any operation such as storing, retrieving, updating or deleting records in the table that hits the database.
What is the purpose of setAutoCommit( )
It is set as
ConnectionObject.setAutoComit();
after any updates through the program cannot be effected to the database.We have commit the transctions .For this puprpose we can set AutoCommit flag to Connection Object.
What are the three statements in JDBC & differences between them
which is used to run simple sql statements like select and update
2. PrepareStatment is used to run Pre compiled sql.
3. CallableStatement is used to execute the stored procedures.
What is stored procedure. How do you create stored procedure ?
Stored procedures is a group of SQL statements that performs a logical unit and performs a particular task.
Stored procedures are used to encapsulate a set of operations or queries to execute on data.
Stored Procedure is a stored program in database, PL/SQL program is a Stored Procedure. Stored Procedures can be called from java by CallableStatement
A precompiled collection of SQL statements stored under a name and processed as a unit.
Stored procedures can:
1.Accept input parameters and return multiple values in the form of output parameters to the calling procedure or batch.
2.Contain programming statements that perform operations in the database, including calling other procedures.
3.Return a status value to a calling procedure or batch to indicate success or failure (and the reason for failure).
What are batch updates?
Batch Update facility allows multiple update operations to be submitted to a database for processing at once. Using batch updates will improve the performance.
What is the difference between Resultset and Rowset
A RowSet is a disconnected, serializable version of a JDBC ResultSet.
The RowSet is different than other JDBC interfaces in that you can write a RowSet to be vendor neutral. A third party could write a RowSet implementation that could be used with any JDBC-compliant database. The standard implementation supplied by Sun uses a ResultSet to read the rows from a database and then stores those rows as Row objects in a Vector inside the RowSet. In fact, a RowSet implementation could be written to get its data from any source. The only requirement is that the RowSet acts as if it was a ResultSet. Of course, there is no reason that a vendor couldn't write a RowSet implementation that is vendor specific.
The standard implementations have been designed to provide a fairly good range of functionality. The implementations provided are:
CachedRowSetImpl - This is the implementation of the RowSet that is closest to the definition of RowSet functionality that we discussed earlier. There are two ways to load this RowSet. The execute ( ) method will load the RowSet using a Connection object. The populate( ) method will load the RowSet from a previously loaded ResultSet.
WebRowSetImpl - This is very similar to the CachedRowSetImpl (it is a child class) but it also includes methods for converting the rows into an XML document and loading the RowSet with an XML document. The XML document can come from any Stream or Reader/Writer object. This could be especially useful for Web Services.
JdbcRowSetImpl - This is a different style of implementation that is probably less useful in normal circumstances. The purpose of this RowSet is to make a ResultSet look like a JavaBean. It is not serializable and it must maintain a connection to the database.
The remaining two implementations are used with the first three implementations:
FilteredRowSetImpl - This is used to filter data from an existing RowSet. The filter will skip records that don't match the criteria specified in the filter when a next() is used on the RowSet.
JoinRowSetImpl - This is used to simulate a SQL join command between two or more RowSet objects.
What are the steps for connecting to the database using JDBC
Using DriverManager:
1. Load the driver class using class.forName(driverclass) and class.forName() loads the driver class and passes the control to DriverManager class
2. DriverManager.getConnection() creates the connection to the databse
Using DataSource.
DataSource is used instead of DriverManager in Distributed Environment with the help of JNDI.
1. Use JNDI to lookup the DataSource from Naming service server.
3. DataSource.getConnection method will return Connection object to the database
What is Connection Pooling ?
Connection pooling is a cache of data base connections that is maintained in memory , so that the connections may be reuse.
Connection pooling is a place where a set of connections are kept and are used by the different programers with out creating conncections to the database(it means there is a ready made connection available for the programmers where he can use). After using the connection he can send back that connection to the connection pool. Number of connections in connection pool may vary.
How do you implement Connection Pooling
Connection Pooling can be implemented by the following way.
* A javax.sql.ConnectionPoolDataSource interface that serves as a resource manager connection factory for pooled java.sql.Connection objects. Each database vendors provide the implementation for that interface.
For example, the oracle vendors implementation is as follows:
oracle.jdbc.pool.oracleConnectionPoolDataSource Class.
• A javax.sql.PooledConnection interface encapsulates the physical connection for the database. Again, the vendor provides the implementation.
What Class.forName( ) method will do
Class.forName() is used to load the Driver class which is used to connect the application with Database. Here Driver class is a Java class provided by Database vendor.
What is the difference between JDBC 1.0 and JDBC 2.0
The JDBC 2.0 API includes many new features in the java.sql package as well as the new Standard Extension package, javax.sql. This new JDBC API moves Java applications into the world of heavy-duty database computing. New features in the java.sql package include support for SQL3 data types, scrollable result sets, programmatic updates, and batch updates. The new JDBC Standard Extension API, an integral part of Enterprise JavaBeans (EJB) technology, allows you to write distributed transactions that use connection pooling, and it also makes it possible to connect to virtually any tabular data source, including files and spread sheets.
The JDBC 2.0 API includes many new features like
1. Scrollable result sets
2. Batch updates
3. Connection Pooling
4. Distributed transactions
5. set autocomit ( )
What is JDBC?
JDBC is a layer of abstraction that allows users to choose between databases. It allows you to change to a different database engine and to write to a single API. JDBC allows you to write database applications in Java without having to concern yourself with the underlying details of a particular database.
What are the two major components of JDBC?
One implementation interface for database manufacturers, the other implementation interface for application and applet writers.
What is JDBC Driver interface?
The JDBC Driver interface provides vendor-specific implementations of the abstract classes provided by the JDBC API. Each vendors driver must provide implementations of the java.sql.Connection,Statement,PreparedStatement, CallableStatement, ResultSet and Driver.
What are the common tasks of JDBC?
Create an instance of a JDBC driver or load JDBC drivers through jdbc.drivers
Register a driver
Specify a database
Open a database connection
Submit a query
Receive results
What packages are used by JDBC?
There are 8 packages: java.sql.Driver, Connection,Statement, PreparedStatement, CallableStatement, ResultSet, ResultSetMetaData, DatabaseMetaData.
What are the flow statements of JDBC?
A URL string -->getConnection-->DriverManager-->Driver-->Connection-->Statement-->executeQuery-->ResultSet.
1). Register the Driver
2) load the Driver
3)get the connection
4) create the statement
5) Execute the query
6) fetch the results with ResultSet
What are the steps involved in establishing a connection?
This involves two steps: (1) loading the driver and (2) making the connection.
How can you load the drivers?
Loading the driver or drivers you want to use is very simple and involves just one line of code. If, for example, you want to use the JDBC-ODBC Bridge driver, the following code will load it:
Eg. Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Your driver documentation will give you the class name to use. For instance, if the class name is jdbc.DriverXYZ , you would load the driver with the following line of code:
E.g. Class.forName("jdbc.DriverXYZ");
What Class.forName will do while loading drivers?
It is used to create an instance of a driver and register it with the DriverManager. When you have loaded a driver, it is available for making a connection with a DBMS.
How can you make the connection?
In establishing a connection is to have the appropriate driver connect to the DBMS. The following line of code illustrates the general idea:
E.g.
String url = "jdbc:odbc:Fred";
Connection con = DriverManager.getConnection(url, "Fernanda", "J8");
How can you create JDBC statements?
A Statement object is what sends your SQL statement to the DBMS. You simply create a Statement object and then execute it, supplying the appropriate execute method with the SQL statement you want to send. For a SELECT statement, the method to use is executeQuery. For statements that create or modify tables, the method to use is executeUpdate. E.g. It takes an instance of an active connection to create a Statement object. In the following example, we use our Connection object con to create the Statement object stmt :
Statement stmt = con.createStatement();
How can you retrieve data from the ResultSet?
First JDBC returns results in a ResultSet object, so we need to declare an instance of the class ResultSet to hold our results. The following code demonstrates declaring the ResultSet object rs.
E.g.
ResultSet rs = stmt.executeQuery("SELECT COF_NAME, PRICE FROM COFFEES");
Second:
String s = rs.getString("COF_NAME");
The method getString is invoked on the ResultSet object rs , so getString will retrieve (get) the value stored in the column COF_NAME in the current row of rs
What are the different types of Statements?
1. Create Statement : For Simple statement used for static query.
2.Prepared Statement :For a runtime / dynamic query .Where String is a dynamic query you want to execute
3. Callable Statement (Use prepareCall) : //For Stored procedure Callable statement, where sql is stored procedure.
try
{
Connection conn = DriverManager.getConnection("URL",'USER"."PWD");
Statement stmt = conn.createStatement();
PreparedStatement pstmt = conn.prepareStatement(String sql);
CallableStatement cstmt = conn.prepareCall(String sql);
}
catch (SQLException ee)
{
ee.printStackTrace();
}
Don't forget all the above statements will throw the SQLException, so we need to use try catch for the same to handle the exception.
How can you use PreparedStatement?
This special type of statement is derived from the more general class, Statement. If you want to execute a Statement object many times, it will normally reduce execution time to use a PreparedStatement object instead. The advantage to this is that in most cases, this SQL statement will be sent to the DBMS right away, where it will be compiled. As a result, the PreparedStatement object contains not just an SQL statement, but an SQL statement that has been precompiled. This means that when the PreparedStatement is executed, the DBMS can just run the PreparedStatement 's SQL statement without having to compile it first.
E.g. PreparedStatement updateSales = con.prepareStatement("UPDATE COFFEES SET SALES = ? WHERE COF_NAME LIKE ?");
How to call a Stored Procedure from JDBC?
The first step is to create a CallableStatement object. As with Statement an and PreparedStatement objects, this is done with an open Connection object. A CallableStatement object contains a call to a stored procedure;
E.g.
CallableStatement cs = con.prepareCall("{call SHOW_SUPPLIERS}");
ResultSet rs = cs.executeQuery();
How to Retrieve Warnings?
SQLWarning objects are a subclass of SQLException that deal with database access warnings. Warnings do not stop the execution of an application, as exceptions do; they simply alert the user that something did not happen as planned. A warning can be reported on a Connection object, a Statement object (including PreparedStatement and CallableStatement objects), or a ResultSet object. Each of these classes has a getWarnings method, which you must invoke in order to see the first warning reported on the calling object
E.g.
SQLWarning warning = stmt.getWarnings();
if (warning != null) {
while (warning != null) {
System.out.println("Message: " + warning.getMessage());
System.out.println("SQLState: " + warning.getSQLState());
System.out.print("Vendor error code: ");
System.out.println(warning.getErrorCode());
warning = warning.getNextWarning();
}
}
How to Make Updates to Updatable Result Sets?
Another new feature in the JDBC 2.0 API is the ability to update rows in a result set using methods in the Java programming language rather than having to send an SQL command. But before you can take advantage of this capability, you need to create a ResultSet object that is updatable. In order to do this, you supply the ResultSet constant CONCUR_UPDATABLE to the createStatement method.
E.g.
Connection con = DriverManager.getConnection("jdbc:mySubprotocol:mySubName");
Statement stmt = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE);
ResultSet uprs = ("SELECT COF_NAME, PRICE FROM COFFEES");
SERVLETS
Web Components
•Servlets
•Java Server Pages (JSP)
•Tags and Tag Libraries
What’s a Servlet?
•Java’s answer to CGI programming
•Program runs on Web server and builds pages on the fly
•When would you use servlets?
–Data changes frequently e.g. weather-reports
–Page uses information from databases e.g. on-line stores
–Page is based on user-submitted data e.g search engines
Servlet Class Hierarchy
•javax.servlet.Servlet
–Defines methods that all servlets must implement
•init()
•service()
•destroy()
•javax.servlet.GenericServlet
–Defines a generic, protocol-independent servlet
•javax.servlet.http.HttpServlet
–To write an HTTP servlet for use on the Web
•doGet()
•doPost()
•javax.servlet.ServletConfig
–A servlet configuration object
–Passes information to a servlet during initialization
•Servlet.getServletConfig()•javax.servlet.ServletContext
–To communicate with the servlet container
–Contained within the ServletConfig object
•ServletConfig.getServletContext()•javax.servlet.ServletRequest
–Provides client request information to a servlet
•javax.servlet.ServletResponse
–Sending a response to the client
Basic Servlet Structure
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class Hello World extends HttpServlet {
// Handle get request public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// request – access incoming HTTP headers and HTML form data // response - specify the HTTP response line and headers
// (e.g. specifying the content type, setting cookies).
PrintWriter out = response.getWriter(); //out - send content to browser
out.println("Hello World");
}
}
Servlet Life Cycle
•Loading and Instantiation
•Initialization
•Request Handling
•End of Service
Session Tracking
•Typical scenario – shopping cart in online store
•Necessary because HTTP is a "stateless" protocol
•Session Tracking API allows you to
–look up session object associated with current request
–create a new session object when necessary
–look up information associated with a session
–store information in a session
–discard completed or abandoned sessions
Session Tracking API - I
•Looking up a session object
–HttpSession session = request.getSession(true);
–Pass true to create a new session if one does not exist
•Associating information with session
–session.setAttribute(“user”,request.getParameter(“name”))
–Session attributes can be of any type
•Looking up session information
–String name = (String) session.getAttribute(“user”)
Session Tracking API - II
•getId : –the unique identifier generated for the session
•isNew : –true if the client (browser) has never seen the session
•getCreationTime : –time in milliseconds since session was made
•getLastAccessedTime : –time in milliseconds since the session was last sent from client
•getMaxInactiveInterval : –# of seconds session should go without access before being invalidated . –negative value indicates that session should never timeout
Javax.Servlet Interface Classes
Servlet Genericservlet
ServletRequest ServletInputStream
ServletResponce ServletOutputStream
ServletConfig ServletException
ServletContext UnavailableException
SingleThreadModel -
Javax.Servlet.Http Classes
HttpServletRequest Cookie
HttpServletResponse HttpServlet
HttpSession HttpSessionBindingEvent
HttpSessionContext HttpUtils
HttpSessionBindingListener -
Exceptions
ServletException
UnavailableException
SERVLETS
1. What is the servlet?
Servlets are modules that extend request/response-oriented servers, such as Java-enabled web servers. For example, a servlet may be responsible for taking data in an HTML order-entry form and applying the business logic used to update a company's order database.
-Servlets are used to enhance and extend the functionality of Webserver.
-Servlets handles Java and HTML separately.
2. What are the uses of Servlets?
A servlet can handle multiple requests concurrently, and can synchronize requests. This allows servlets to support systems such as on-line conferencing. Servlets can forward requests to other servers and servlets. Thus servlets can be used to balance load among several servers that mirror the same content, and to partition a single logical service over several servers, according to task.
3. What are the characters of Servlet?
As Servlet are written in java, they can make use of extensive power of the JAVA API,such as networking and URL access,multithreading,databaseconnectivity,RMI object serialization.
Efficient : The initilazation code for a servlet is executed only once, when the servlet is executed for the first time.
Robust : provide all the powerful features of JAVA, such as Exception handling and garbage collection.
Portable: This enables easy portability across Web Servers.
Persistance : Increase the performance of the system by executing features data access.
4. What is the difference between JSP and SERVLETS
Servlets : servlet tieup files to independently handle the static presentation logic and dynamic business logic , due to this a changes made to any file requires recompilation of the servlet.
- The servlet is Pre-Compile.
JSP : Facilities segregation of work profiles to Web-Developer and Web-Designer , Automatically incorporates changes made to any file (PL & BL) , no need to recompile.
Web-Developer write the code for Bussiness logic whereas Web-Designer designs the layout for the WebPage by HTML & JSP.
- The JSP is Post-Compile.
5. What are the advantages using servlets than using CGI?
Servlets provide a way to generate dynamic documents that is both easier to write and faster to run. It is efficient, convenient, powerful, portable, secure and inexpensive. Servlets also address the problem of doing server-side programming with platform-specific APIs. They are developed with Java Servlet API, a standard Java extension.
6. What is the difference between servlets and applets?
Servlets are to servers. Applets are to browsers. Unlike applets, however, servlets have no graphical user interface.
7. What is the difference between GenericServlet and HttpServlet?
GenericServlet is for servlets that might not use HTTP, like for instance FTP service.As of only Http is implemented completely in HttpServlet. The GenericServlet has a service() method that gets called when a client request is made. This means that it gets called by both incoming requests and the HTTP requests are given to the servlet as they are.
GenericServlet belongs to javax.servlet package
GenericServlet is an abstract class which extends Object and implements Servlet, ServletConfig and java.io.Serializable interfaces.
The direct subclass to GenericServlet is HttpServlet.It is a protocol-independent servlet
8. What are the differences between GET and POST service methods?
Get Method : Uses Query String to send additional information to the server.
-Query String is displayed on the client Browser.
Query String : The additional sequence of characters that are appended to the URL ia called Query String. The length of the Query string is limited to 255 characters.
-The amount of information you can send back using a GET is restricted as URLs can only be 1024 characters.
POST Method : The Post Method sends the Data as packets through a separate socket connection. The complete transaction is invisible to the client. The post method is slower compared to the Get method because Data is sent to the server as separate packates.
--You can send much more information to the server this way - and it's not restricted to textual data either. It is possible to send files and even binary data such as serialized Java objects!
9. What is the servlet life cycle?
In Servlet life cycles are,
init(),services(),destory().
Init( ) : Is called by the Servlet container after the servlet has ben Instantiated.
--Contains all information code for servlet and is invoked when the servlet is first loaded.
-The init( ) does not require any argument , returns a void and throws Servlet Exception.
-If init() executed at the time of servlet class loading.And init() executed only for first user.
-You can Override this method to write initialization code that needs to run only once, such as loading a driver , initializing values and soon, Inother case you can leave normally blank.
Public void init(ServletConfig Config) throws ServletException
Service( ) : is called by the Servlet container after the init method to allow the servlet to respond to a request.
-Receives the request from the client and identifies the type of request and deligates them to doGet( ) or doPost( ) for processing.
Public void service(ServletRequest request,ServletResponce response) throws ServletException, IOException
Destroy( ) : The Servlet Container calls the destroy( ) before removing a Servlet Instance from Sevice.
-Executes only once when the Servlet is removed from Server.
Public void destroy( )
If services() are both for get and post methods.
-So if u want to use post method in html page,we use doPost() or services() in servlet class.
-if want to use get methods in html page,we can use doGet() or services() in servlet calss.
-Finally destory() is used to free the object.
10. What is the difference between ServletContext and ServletConfig?
Both are interfaces.
Servlet Config():The servlet engine implements the ServletConfig interface in order to pass configuration information to a servlet. The server passes an object that implements the ServletConfig interface to the servlet's init() method.
A ServletConfig object passes configuration information from the server to a servlet. ServletConfig also includes ServletContext object.
getParameter( ) , getServletContext( ) , getServletConfig( ), GetServletName( )
Servlet Context(): The ServletContext interface provides information to servlets regarding the environment in which they are running. It also provides standard way for servlets to write events to a log file.
ServletContext defines methods that allow a servlet to interact with the host server. This includes reading server-specific attributes, finding information about particular files located on the server, and writing to the server log files. If there are several virtual servers running, each one may return a different ServletContext.
getMIMEType( ) , getResourse( ), getContext( ),getServerInfo( ),getServletContetName( )
11. Can I invoke a JSP error page from a servlet?
Yes, you can invoke the JSP error page and pass the exception object to it from within a servlet. The trick is to create a request dispatcher for the JSP error page, and pass the exception object as a javax.servlet.jsp.jspException request attribute. However, note that you can do this from only within controller servlets.
12. If your servlet opens an OutputStream or PrintWriter, the JSP engine will throw the following translation error:
java.lang.IllegalStateException: Cannot forward as OutputStream or Writer has already been obtained
13. Can I just abort processing a JSP?
Yes.Because your JSP is just a servlet method,you can just put (whereever necessary) a < % return; %>
14. What is a better approach for enabling thread-safe servlets and JSPs? SingleThreadModel Interface or Synchronization?
Although the SingleThreadModel technique is easy to use, and works well for low volume sites, it does not scale well. If you anticipate your users to increase in the future, you may be better off implementing explicit synchronization for your shared data. The key however, is to effectively minimize the amount of code that is synchronzied so that you take maximum advantage of multithreading.
Also, note that SingleThreadModel is pretty resource intensive from the server's perspective. The most serious issue however is when the number of concurrent requests exhaust the servlet instance pool. In that case, all the unserviced requests are queued until something becomes free - which results in poor performance. Since the usage is non-deterministic, it may not help much even if you did add more memory and increased the size of the instance pool.
15. If you want a servlet to take the same action for both GET and POST request, what should you do?
Simply have doGet call doPost, or vice versa.
16. Which code line must be set before any of the lines that use the PrintWriter?
setContentType() method must be set before transmitting the actual document.
17. How HTTP Servlet handles client requests?
An HTTP Servlet handles client requests through its service method. The service method supports standard HTTP client requests by dispatching each request to a method designed to handle that request.
18. What is the Servlet Interface?
The central abstraction in the Servlet API is the Servlet interface. All servlets implement this interface, either directly or, more commonly, by extending a class that implements it such as HttpServlet.
Servlets-->Generic Servlet-->HttpServlet-->MyServlet.
The Servlet interface declares, but does not implement, methods that manage the servlet and its communications with clients. Servlet writers provide some or all of these methods when developing a servlet.
19. a servlet accepts a call from a client, it receives two objects. What are they?
ServeltRequest: which encapsulates the communication from the client to the server.
ServletResponse: which encapsulates the communication from the servlet back to the
Client.
ServletRequest and ServletResponse are interfaces defined by the javax.servlet package.
20. What information that the ServletRequest interface allows the servlet access to?
Information such as the names of the parameters passed in by the client, the protocol (scheme) being used by the client, and the names of the remote host that made the request and the server that received it. The input stream, ServletInputStream.Servlets use the input stream to get data
from clients that use application protocols such as the HTTP POST and PUT methods.
21. What information that the ServletResponse interface gives the servlet methods for replying to the client?
It Allows the servlet to set the content length and MIME type of the reply. Provides an output stream, ServletOutputStream and a Writer through which the servlet can send the reply data.
22. Difference between single thread and multi thread model servlet
A servlet that implements SingleThreadModel means that for every request, a single servlet instance is created. This is not a very scalable solution as most web servers handle multitudes of requests. A multi-threaded servlet means that one servlet is capable of handling many requests which is the way most servlets should be implemented.
a. A single thread model for servlets is generally used to protect sensitive data ( bank account operations ).
b. Single thread model means instance of the servlet gets created for each request recieved. Its not thread safe whereas in multi threaded only single instance of the servlet exists for what ever # of requests recieved. Its thread safe and is taken care by the servlet container.
c. A servlet that implements SingleThreadModel means that for every request, a single servlet instance is created. This is not a very scalable solution as most web servers handle multitudes of requests. A multi-threaded servlet means that one servlet is capable of handling many requests which is the way most servlets should be implemented.
A single thread model for servlets is generally used to protect sensitive data ( bank account operations ).
23. What is servlet context and what it takes actually as parameters?
Servlet context is an object which is created as soon as the Servlet gets initialized.Servlet context object is contained in Servlet Config. With the context object u can get access to specific
resource (like file) in the server and pass it as a URL to be displayed as a next screen with the help of RequestDispatcher
eg :-
ServletContext app = getServletContext();
RequestDispatcher disp;
if(b==true)
disp = app.getRequestDispatcher
("jsp/login/updatepassword.jsp");
else
disp = app.getRequestDispatcher
("jsp/login/error.jsp");
this code will take user to the screen depending upon the value of b.
in ServletContext u can also get or set some variables which u would
like to retreive in next screen.
eg
context.setAttribute("supportAddress", "temp@temp.com");
Better yet, you could use the web.xml context-param element to
designate the address, then read it with the getInitParameter method
of ServletContext.
24. Can we call destroy() method on servlets from service method?
destroy() is a servlet life-cycle method called by servlet container to kill the instance of the servlet. "Yes". You can call destroy() from within the service(). It will do whatever logic you have in destroy() (cleanup, remove attributes, etc.) but it won't "unload" the servlet instance itself. That can only be done by the container
25. What is the use of ServletConfig and ServletContext..?
An interface that describes the configuration parameters for a servlet. This is passed to the servlet when the web server calls its init() method. Note that the servlet should save the reference to the ServletConfig object, and define a getServletConfig() method to return it when asked. This interface defines how to get the initialization parameters for the servlet and the context under which the servlet is running.
An interface that describes how a servlet can get information about the server in which it is running. It can be retrieved via the getServletContext() method of the ServletConfig object.
26. What is difference between forward() and sendRedirect().. ? Which one is faster then other and which works on server?
Forward( ) : javax.Servlet.RequestDispatcher interface.
-RequestDispatcher.forward( ) works on the Server.
-The forward( ) works inside the WebContainer.
-The forward( ) restricts you to redirect only to a resource in the same web-Application.
-After executing the forward( ), the control will return back to the same method from where the forward method was called.
-the forward( ) will redirect in the application server itself, it does’n come back to the client.
- The forward( ) is faster than Sendredirect( ) .
To use the forward( ) of the requestDispatcher interface, the first thing to do is to obtain RequestDispatcher Object. The Servlet technology provides in three ways.
1. By using the getRequestDispatcher( ) of the javax.Servlet.ServletContext interface , passing a String containing the path of the other resources, path is relative to the root of the ServletContext.
RequestDispatcher rd=request.getRequestDispatcher(“secondServlet”);
Rd.forward(request, response);
2. getRequestDispatcher( ) of the javax.Servlet.Request interface , the path is relative to current HtpRequest.
RequestDispatcher rd=getServletContext( ).getRequestDispatcher(“servlet/secondServlet”);
Rd.forward(request, response);
3. By using the getNameDispatcher( ) of the javax.Servlet.ServletContext interface.
RequestDispatcher rd=getServletContext( ).getNameDispatcher(“secondServlet”);
Rd.forward(request, response);
Sendredirect( ) : javax.Servlet.Http.HttpServletResponce interface
-RequestDispatcher.SendRedirect( ) works on the browser.
-The SendRedirect( ) allows you to redirect trip to the Client.
-The SendRedirect( ) allows you to redirect to any URL.
-After executing the SendRedirect( ) the control will not return back to same method.
-The Client receives the Http response code 302 indicating that temporarly the client is being redirected to the specified location , if the specified location is relative , this method converts it into an absolute URL before redirecting.
-The SendRedirect( ) will come to the Client and go back,.. ie URL appending will happen.
Response. SendRedirect( “absolute path”);
Absolutepath – other than application , relative path - same application.
When you invoke a forward request, the request is sent to another resource on the server, without the client being informed that a different resource is going to process the request. This process occurs completely with in the web container. When a sendRedirtect method is invoked, it causes the web container to return to the browser indicating that a new URL should be requested. Because the browser issues a completely new request any object that are stored as request attributes before the redirect occurs will be lost. This extra round trip a redirect is slower than forward.
27. do we have a constructor in servlet ? can we explictly provide a constructor in servlet programme as in java program ?
We can have a constructor in servlet .
Session : A session is a group of activities that are performed by a user while accesing a particular website.
Session Tracking :The process of keeping track of settings across session is called session tracking.
Hidden Form Fields : Used to keep track of users by placing hidden fields in the form.
-The values that have been entered in these fields are sent to the server when the user submits the Form.
URL-rewriting : this is a technique by which the URL is modified to include the session ID of a particular user and is sent back to the Client.
-The session Id is used by the client for subsequent transactions with the server.
Cookies : Cookies are small text files that are used by a webserver to keep track the Users.
A cookie is created by the server and send back to the client , the value is in the form of Key-value pairs. Aclient can accept 20 cookies per host and the size of each cookie can be maximum of 4 bytes each.
HttpSession : Every user who logs on to the website is autometacally associated with an HttpSession Object.
-The Servlet can use this Object to store information about the users Session.
-HttpSession Object enables the user to maintain two types of Data.
ie State and Application.
28. How to communicate between two servlets?
Two ways:
a. Forward or redirect from one Servlet to another.
b. Load the Servlet from ServletContext and access methods.
29. How to get one Servlet's Context Information in another Servlet?
Access or load the Servlet from the Servlet Context and access the Context Information
30. The following code snippet demonstrates the invocation of a JSP error page from within a controller servlet:
protected void sendErrorRedirect(HttpServletRequest request,
HttpServletResponse response, String errorPageURL, Throwable e) throws
ServletException, IOException {
request.setAttribute ("javax.servlet.jsp.jspException", e);
getServletConfig().getServletContext().
getRequestDispatcher(errorPageURL).forward(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
{
try {
// do something
} catch (Exception ex) {
try {
sendErrorRedirect(request,response,"/jsp/MyErrorPage.jsp",ex);
} catch (Exception e) {
e.printStackTrace();
}
} }
JSP (JavaServer Pages)
Why JSP Technology?
•Servlets are good at running logic
–Not so good at producing large amounts of output
–out.write() is ugly
•JSP pages are great at producing lots of textual output
–Not so good at lots of logic
–<% %> is ugly
How does it Work
•“JSP page”
–Mixture of text, Script and directives
–Text could be text/ html, text/ xml or text/ plain
•“JSP engine”
–‘Compiles’ page to servlet
–Executes servlet’s service() method
•Sends text back to caller
•Page is
–Compiled once
–Executed many times
Anatomy of a JSP
<%@ page language=“java” contentType=“text/html” %>
The following information was saved:
User Name:
Welcome!
JSP Elements
•Directive Elements : –Information about the page
–Remains same between requests
–E.g., scripting language used
•Action Elements : –Take action based on info required at request-time
•Standard
•Custom (Tags and Tag Libraries)
•Scripting Elements
–Add pieces of code to generate output based on conditions
Directives
•Global information used by the “JSP engine”
•Of form <%@ directive attr_ list %>
•Or
–Directive could be
•Page
•Include
•Taglib
–E. g.,
<%@ page info=“ written by DevelopMentor” %>
<%@ include file =“\ somefile. txt” %>
<%@ taglib uri = tags prefix=“ foo” %>
Actions Within a JSP Page
•Specifies an action to be carried out by the “JSP engine”
•Standard or custom
–Standard must be implemented by all engines
–Custom defined in tag libraries
•Standard actions ‘scoped’ by ‘jsp’ namespace
•Have name and attributes
- The current date at the server is:
- Date:
- Month:
Standard JSP Actions :
•jsp:useBean
•jsp:getProperty
•jsp:setProperty
•jsp:include
•jsp:forward
•jsp:param
•jsp:plugin
Scriptlets
•Of form <% /* code goes here*/ %>
–Gets copied into _ jspService method of generated servlet
•Any valid Java code can go here
CODE: OUTPUT
<% int j; %>
<% for (j = 0; j < 3; j++) {%>
<% out. write(""+ j); %>
<% } %>
Declarations (<%! … %>)
•Used to declare class scope variables or methods
<%! int j = 0; %>
•Gets declared at class- level scope in the generated servlet
•public class SomeJSP extends HttpServlet implements HttpJspPage {
…
int j = 0;
void _jspService(…) {}
}
Declarations (<%! … %>)
•Used to declare class scope variables or methods
<%! int j = 0; %>
•Gets declared at class- level scope in the generated servlet
•public class SomeJSP extends HttpServlet implements HttpJspPage {
…
int j = 0;
void _jspService(…) {}
}
JSP to Servlet Translation
<%@ page import="javax.ejb.*,javax.naming.*,java.rmi.* ,java.util.*" %>
<% String checking = null;
String name = null;
checking = request.getParameter("catch");
if (checking != null) {
name = request.getParameter("name");%>
Hello <%=name%>
<% } %>
Generated Servlet…
public void _jspService(HttpServletRequest request ,
HttpServletResponse response)
throws ServletException ,IOException {
out.write("
String checking = null;
String name = null;
checking = request.getParameter("catch");
if (checking != null) {
name = request.getParameter("name");
out.write("\r\n\t\t Hello " );
out.print(name);
out.write("\r\n\t\t" );
}
out.write("\r\n\t\t
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