j2ee overview

J2EE Overview ver 1.0 © Wipro TechnologiesTalent Transformation

J2EE Overview


Objectives

In this session, you will learn to:

• Identify the characteristics of different Java Platforms

• Identify the challenges of an enterprise application

• Describe J2EE architecture

• Define the role of various J2EE technologies


Java 2 Editions


Issues in Enterprise Applications

• Transactions

• State management

• Multithreading

• Resource pooling

• Security


Java 2 Platform, Enterprise Edition

J2EEJ2EE

RMI

JNDI

JDBC

JavaMail

Servlets JSP Java IDL

EJB

JMS

JTA

Connectors

XML

Java 2: Standard ed.


J2EE Architecture


J2EE

Services Java Technology

Web Servlets/ JSPs (HTML/ XML)

Database Access Java DataBase Connectivity (JDBC™)

Naming And Directory Java Naming and Directory Interface

Messaging Java Message Service (JMS)

Email Access JavaMail™

Protocol JavaIDL, Remote Method Invocation

(CORBA compatible)

Transaction Object Transaction Service (OTS),

Java Transaction Service (JTS),

Java Transaction API (JTA)


Naming Services

• Provide J2EE components with access to a JNDI naming environment– J2EE component locates its environment naming context

using JNDI interfaces


Java Naming and Directory Interface

• A standard for Naming and directory services

• EJB strictly relies on JNDI for looking up distributed components across the network

• e.g. Novell’s NDS and the internet standard LDAP– Each one is accessed differently

– Stores info in a proprietary way

• JNDI bridges the gap between different directory services: provides portable interface


JNDI Interface


Transaction Scenario...

What’s Wrong with This Code?try {// Withdraw funds from account 1}catch (Exception e) {// If an error occurred, do not proceed.return;} }try {// Otherwise, deposit funds into account 2

}catch (Exception e) {// If an error occurred, do not proceed,// and redeposit the funds back into account 1.return;}


Transaction Definition

• An atomic unit of work

• Can consist of multiple operations from multiple objects

• Example: withdrawing money from an account using an automatic teller machine

• Can support the following features:– Distribution across a network

– Two - phase commits

– Nested transactions


Transaction Participants

• Resource has transactional state– Example: Database connection

• Resource manager can commit and rollback– Example: JDBC driver

• Application server assists in managing usage of transactional resources by beans– Example: EJB server


Transaction Participants

• Transaction manager:– Controls state of transaction, two- phase commit

– Coordinates/ controls all resource managers within transaction

• Transactional application obtains a limited access to the transaction manager:– Client application

– Enterprise bean


Transactions and the ACID Properties

• As we have seen, exceptions are not enough for enterprise computing– Code is non- deterministic

• Transactions guarantee determinism

• Transactions give you four virtues, called the ACID properties:– Atomicity

– Consistency

– Isolation

– Durability


Transaction Services

• J2EE transactions are flat

• J2EE platform implicitly handles many transaction details

• A Transaction is a unit of work that makes a set of guarantees about its execution


Java Transaction API (JTA) and Java Transaction Service (JTS)

• JTA: – High level transaction interface: EJB clients use JTA

– Required to perform transactions in Java

• JTS:– Low-level transaction interface: EJB uses behind the scene

– Makes possible multiple vendors to collaborate for distributed transactions


Service Technology

• Provide access to database, transactions, naming and directory services and enterprise information systems

• JDBC API

• Java Transaction API and Service

• Java Naming and Directory Interface

• Connector Architecture

• Communication Techniques– Internet protocols

– RMI protocols

– OMG protocols

– Messaging technologies


Introduction to RMI

• Distributed Computing

• RPC

• RMI


Features of RMI

• Remote invocations of methods on objects in different JVM’s

• Simple to write reliable distributed applications

• RMI is transparent


RMI Architecture

Client Program

Stub

RRL

Transport Layer

Server Program

Skeleton Layer

RRL


Writing a Simple RMI program

• Write the Remote Object program//Product.javaimport java.rmi.*;import java.rmi.server.*;interface Product extends Remote{public String getDescription() throws RemoteException;}



2) Write the Remote Server Program

//ProductImpl.javaimport java.rmi.*;import java.rmi.server.*;public class ProductImpl extends UnicastRemoteObject implements Product{ private String str;

public ProductImpl(String d) throws RemoteException{str = d;

}public String getDescription() throws RemoteException{

return "Product Name : "+str;}



2) Write the Remote Server Program …contnd

public static void main(String a[]){ try{

ProductImpl p1= new ProductImpl("Washing Machine");ProductImpl p2= new ProductImpl("Microwave Oven");

Naming.rebind("wash",p1);Naming.rebind("oven",p2);

}catch(Exception e) {System.out.println("ERROR: "+e);e.printStackTrace();

}}}



3) Write the Client program

import java.rmi.*;import java.rmi.server.*;public class ProductClient{

public static void main(String a[]){try{

Product c1=(Product)Naming.lookup("wash");Product c2=(Product)Naming.lookup("oven");System.out.println(c1.getDescription());System.out.println(c2.getDescription());

}catch(Exception e){System.out.println("Error: "+ e);}System.exit(0);}}


JavaMail

• The JavaMail API allows your applications to use e-mail capabilities

• JavaMail defines a set of interfaces to which you write your application code, and those interfaces shield your code from the specific protocols or mail service implementations used

• Based on JavaBeans Activation Framework (JAF) to encapsulate message data and to handle interactions with that data


Java Messaging Service

• JMS allows Java programs to exchange messages with other Java programs sharing a messaging system.

• Messaging systems are sometimes called Message-Oriented Middleware (MOM)

• JMS API enables communication that is :– Asynchronous

– Reliable


Real Time Example

• Automobile manufacturer– The inventory component can send a message to the factory

component when the inventory level for a product goes below a certain level, so the factory can make more cars.

– The factory component can send a message to the parts components so that the factory can assemble the parts it needs.

– The parts components in turn can send messages to their own inventory and order components to update their inventories and order new parts from suppliers.

– Both the factory and parts components can send messages to the accounting component to update their budgets.

– The business publishes updated catalog items to its sales force and web site.


JMS Architecture

• JMS provider – is a messaging product that

implements the JMS interfaces and provides administrative and control features

• Administered objects– pre-configured JMS objects

created by an administrator for the use of clients.

• JMS clients– the programs or components

written in the Java programming language that produce and consume messages.

• Messages– the objects that communicate

information between JMS clients.


Publish-Subscribe Messaging


Point- To-Point Messaging


Enterprise JavaBeans

• Enterprise JavaBeans is an architecture for component- based distributed computing:– Customizable at deployment time

– Deployed on a compatible application server

– Portable to other application servers

• Enterprise Beans are components of distributed transaction - oriented enterprise applications


Defining EJB Technology

• EJB servers provide core services to server components:– Transaction

– Security

– Concurrency

– Naming

– Persistence

• EJB technology enhances:– Simplified access to services

– Portability of components across server platforms


Defining EJB Technology

• Is a server component specification (for vendors)

• Separates and defines integration of development stages:– Component creation

– Application assembly

– Application deployment


EJB Developer Roles


EJB Programming Paradigm

• Declarative programming and customizing


EJB Programming Paradigm

• Deploying


EJB Architecture Overview

• Uniform client access whether local or remote

• Home object is a factory for EJBs

• EJB object is the remote object for accessing EJBs


EJB Architecture Overview


EJB Server

• Services:– Transaction support

– Data access

– System resource

– Namespace

• Industry support:– Application/ middleware servers

– Database servers


EJB Container

• Can contain multiple Bean classes or homes– Often created using code generation by tools

– Is normally provided by EJB server vendor

• Is not visible to the client

• Is implemented in different ways by different vendors


EJB Container

• Provides some standard services:– Persistence

– Transaction control

– Security

– EJB instance lifecycle management

– EJB instance identification


Home Interface

• Factory interface for the bean:– Interface provided by EJB developer

– Class generated by vendor tool

• One factory class per bean class

• Factory instance is installed into the server’s naming service


Remote Interface

• Interface is provided by bean developer.

• Implementation is provided by container tools, which include:– Stubs and skeletons

– The EJB Object


EJB Object

• The EJB Object is a wrapper object that acts as a proxy to the EJB instance.– Interface provided by Bean developer

– Implementation class generated by vendor tool

• Each business method has a corresponding wrapper method in the EJB Object– Wrapper method implements container- provided services


Stubs and Skeletons

• Stub is downloaded from server

• Communication between stub and skeleton can be proprietary, yet EJB code is still portable


Types of EJBs


J2EE Components and Containers


Summary

In this session, you learnt to:

• Identify characteristics of different Java Platforms

• Identify the challenges of an enterprise application

• Describe J2EE architecture

• Define the role of various J2EE technologies


References

j2ee overview

Documents

directory java naming

controls state of transaction

jndi interfacesjava

limited access

directory servicesejb

directory interfacea

environment naming context

different directory