EJB Introduction for All New Users

8/10/2019 EJB Introduction for All New Users

1/62

EJB Architecture and Design

CS486

Global Knowledge NetworksInstructor : Dr. V. Juggy

Presentation by:Aravind Vinnakota


2/62

What is EJB?

An EJB is just a collection of Java classesand XML file, bundled into a single unit.

The Java classes must follow certain rulesand provide certain callback methods.

EJB is just a specification. It is not a

product.EJBs are reusable components.


3/62

What is EJB?

EJB is a widely-adopted server-sidecomponent architecture for J2EE.

EJB components are designed toencapsulate business logic, and to protectthe application developer from having to

worry about system level issues.


4/62

Contents

Services provided by EJB container

Circumstances of EJB component usage

How an EJB component looks like?View of an EJB component by client

programmer and EJB developer

Mechanisms by which EJB container provides itsservices

Rules an EJB developer must followand howtouse EJBs in a web architecture?


5/62

Key features of EJB technology

EJB components are server-side componentswritten entirely in the Java programminglanguage

EJB components contain business logic only - no

System-level programming

System-level services (i.e. "plumbing") such astransactions, security, Life-cycle, threading,persistence, etc. are automatically managed for

the EJB component by the EJB server


6/62

Key features of EJB technology

EJB architecture is inherently transactional,distributed, portable, multi-tier, scalable andsecure

EJB components are fully portable across anyEJB server and any OS, work with any client.

Components are declaratively customized

There are four major parts to every bean: thehome interface, the remote interface, theimplementation class and the XML deployment

descriptor


7/62

EJB vs JavaBeans

The JavaBeans architecture is meant toprovide a format for general-purpose

components whereas the EJB architectureprovides a format for encapsulation andmanagement of business logic.

JavaBeans has tier of execution at Clientand EJB has at Server (specificallybusiness logic tier)


8/62

EJB vs JavaBeans

In JavaBeans the runtime executionenvironment provides services like Java

libraries, Java application etc. The EJBruntime environment provides services ofPersistence, declarative transactions and

security, connection pooling and lifecycleservices.


9/62

Varieties of Beans

Session Beans

Stateful session bean

Stateless session bean

Entity Beans

With container-managed persistence

With bean-managed persistence

Message-Driven Beans


10/62

Why use EJBs in your design?

EJB specification provides enterprise-levelservices, that is, it provides software

services that are fundamental to anorganizations purpose.

EJBs API was designed to keep the

application programmer from having toprovide systems-level services, so thatthey are free to concentrate on businesslogic.


11/62

Why use EJBs in your design?

A requirement of any of the servicesprovided by an EJB container like

transactions, scalability, persistence,security, future growth possibilities is anappropriate reason to use EJB in the

design of the application.


12/62

EJB Architecture

J2EE Application Server

EJB Container

Application Logic DataClient

RDBMS

Corba

Mail

RMI

JDBC

Java

Mail

JMS

JTA

Session Bean

Entity Bean

Client

Application


13/62

Roles in EJB Development

EJB provider - a person who developsEJB Components

EJB Deployer - a person responsible fordeploying EJBs in EJB server

Application Server/ EJB Container Vendor

- one who provides application server onwhich the application is deployed


14/62


Application assembler - one who combinethe EJB components with other software

to make a complete applicationSystem administrator - one who manages

the application after it has been deployed

into a target environment.


15/62


EJB

Provider

Application

Assembler

App Server/

EJB Container

Provider

Deployer

System

Administrator


16/62

EJB Container and its Services

A container is an execution environmentfor a component. The component lives in

the container and the container providesthe services for the component.

Similarly, a container lives in an

application server, which provides anexecution environment for it and othercontainers.


17/62

Services provided by an EJB container

Persistence

Ex: simple connection pooling, automatic

persistence, etc. EJBs created withapplication development tools willencapsulate data access in components.


18/62

Services provided by an EJB container

Declarative transactions

Data caching

Declarative Security

Error Handling

Component Framework for Business Logic

Scalability and Fall-Over

Portability

Manageability


19/62

How the Container Provides Services

There are three basic ideas:

First, there are clearly defined responsibilities betweenthe various parts of an application using EJB component

namely the client, the EJB container and the EJBcomponent. The definition of these responsibilities isformally known as a contract.

Second, the servicesthat the container provides are

defined in such a way that they are orthogonalto thecomponent. In other words, security, persistence,transactions are separate from the Java files thatimplement the business logic of the component.


20/62

How the Container Provides Services

Third, the container interposes on eachand every call to an EJB component so

that it can provide its services. In otherwords, the container puts itself betweenthe client and the component on every

single business method call.


21/62

Contracts

EJB Container/Application

Server

Enterprise JavaBean

Client


22/62

Rules for the bean programmer

The developer of the EJB component must implementthe business methods in the implementation class

The bean provider must implement the ejbCreate(),

ejbPostCreate(),ejbRemove()methods and theejbFind()methods if the bean is an entitywith bean managed persistence

The bean provider must define the enterprise beans

homeand remoteinterfaces For session beans, the bean provider must implement

the container callbacks defined in thejavax.ejb.SessionBeaninterface


23/62

Rules for the bean programmer

For entity beans, the provider mustimplement the container callbacks defined

in the javax.ejb.EntityBean interfaceThe bean provider must not use

programming practices that would

interfere with the containers runtimemanagement of the enterprise beaninstances


24/62

Interposition : method call to an EJBContainer from a remote client

First, the client makes a call on the RMIstub

This RMI stub interposes on the methodcall in order to marshal parameters andsend the information across the network

A skeleton on the server side unmarshalsthe parameters and delivers them to theEJB Container


25/62

Interposition diagram

Interposition class

ClientContainer

generated

classEJB

RMI

StubRMI

StubNetwork


26/62

Interposition : from EJBContainer to EJBs

The container will examine the security credentials ofthe caller of the method

It will start or join with any required transactions

It will make any necessary calls to persistence functions

It will trigger various callbacks to allow the EJBComponent to acquire resources

Only after all this is done will the actual business

method be called

Once it is called, the container will do some more workwith transactions, persistence, callbacks and returnsdata or exception to the remote client


27/62

Working with EJBs

The Enterprise JavaBeans specification iswritten for three audiences:

The Client developerThe EJB developer

The EJB container developer


28/62

EJB Clients

EJB Clients are applications that access EJBcomponents in EJB containers. There are twopossible types. The first category is applicationclients which are stand-alone applicationsaccessing the EJB components using the RMI-IIOP protocol. The second category of

application clients are components in the webcontainer. They are java servlets and JSPswhich also access the EJB components via the

RMI-IIOP protocol.


29/62

The Client Developers View

The client has a smaller set of concerns then abean developer with regard to using EJBs.Basically, he need to know :

how to find or create a bean,

how to use its methods and

how to release its resources

The client need not worry about theimplementation of the EJB, callbacks that theEJB container will make on the EJB or nature of

the services provided to the EJB.


30/62

EJBs interface

Home Interface: It is primarily for the life cycleoperations of the bean: creating, finding, andremoving EJBs. The home interface is notassociated with a particular bean, just with atype of bean.

Remote Interface: It is for business methods.

Logically, it represents a particular bean on theserver. The remote interface also provides someinfrastructure methods associated with a beaninstance, rather than a bean type.


31/62

Sample client applicationpseudo code

A client programmer will acquire an EJBs homeinterface through JNDI, and they use this homeinterface to :

Create or find

instance of bean

Execute methods Reference

(Handle)Remove bean


32/62

Client.java

Package orderMgmt;

import java.util.properties;

import java.naming.Context; // for name-to-object findings

import java.naming.InitialContext;// context for naming operationspublic class Client {

try {

Properties prop = new Properties();

// server dependent properties for InitialContext

prop.put(Context.INITIAL_CONTEXT_FACTORY,org.jnp.interfaces.NamingContextFactory);

prop.put(Context.PROVIDER_URL, localhost:1099);

Context ctx = new InitialContext(prop);

Object objref = ctx.lookup(OrderManagement);


33/62

Client contd..

// casting home interface reference to the OrderManagementHome

OrderManagementHome home = (OrderManagementHome)javax.rmi.PortableRemoteObject.narrow(objref,OrderManagementHome.class);

// home interface to create an instance of the OrderManagement

OrderManagement orderManagement = home.create();

// calling placeOrder()

orderManagement.placeOrder("Dan OConnor",

"Wrox books on programming", 1000);orderManagement.remove();

System.out.println("Order successfully placed.");

} catch (Exception e) { e.printStackTrace(); }

} }


34/62

The Bean Programmers view

Main responsibility is write business logic andstructure the code in a particular structure. Thestructure has 4 files, the home interface, remoteinterface, business logic class file and the XML

file.The XML file called the deploymentdescriptor, contains the structural information

about the bean, declares the beans externaldependencies and specifies certain informationabout how services such as transaction and

security work.


35/62

Interface EJBObject

package javax.ejb;

public interface javax.ejb.EJBObject extends java.rmi.Remote {

EJBHome getEJBHome() throws java.rmi.RemoteException;

Handle getHandle() throwsjava.rmi.RemoteException;Object getPrimaryKey() throws java.rmi.RemoteException;

boolean isIdentical(EJBObject obj) throwsjava.rmi.RemoteException;

void remove() throws java.rmi.RemoteException;

}


36/62

OrderManagement code..

package orderMgmt;

import javax.ejb.*;

public interface OrderManagement extends javax.ejb.EJBObject {

public void placeOrder(String custName, String prodName, int

quantity)throws java.rmi.RemoteException;

public void cancelOrder(String custName, String prodName) throws java.rmi.RemoteException;

public boolean isShipped(StringcustName, String prodName)throws java.rmi.RemoteException;

}


37/62

OrderManagementBean code..

package orderMgmt;

import javax.ejb.*;

public class OrderManagementEJB implementsjavax.ejb.SessionBean

{

public void placeOrder(String custName, String prodName, int

quantity) { // ... Business logic ...}

public void cancelOrder(String custName, String prodName)

{ // ... Business logic ...}

public boolean isShipped(String custName, String prodName)

{ // ... Business logic return true; }


38/62

OrderManagementBean code..

public void ejbCreate()

{ // Can be empty }

public void ejbRemove()

{ // Can be empty }

public void ejbActivate()

{ // Can be empty}

public void ejbPassivate()

{ // Can be empty}

public void setSessionContext( SessionContext ctx )

{ // Can be empty}

}


39/62


40/62

OrderManagementHome code..

package orderMgmt;

import javax.ejb.*;

public interface OrderManagementHome extendsjavax.ejb.EJBHome

{

public OrderManagement create()

throws java.rmi.RemoteException, javax.ejb.CreateException;

}


41/62

The xml file : ejb-jar.xml

OrderManagement

orderMgmt.OrderManagementHome

orderMgmt.OrderManagement

orderMgmt.OrderManagementBean

Stateless

Container


42/62

The xml file : ejb-jar.xml

OrderManagement*

Required


43/62

Structure of JAR file

META -INF\

ejb-jar.xml

orderMgmt\OrderManagement.class

OrderManagementHome.class

OrderManagementBean.class


44/62

What you cant do in an EJB component?

You cannot use Reflection API to accessinformation inaccessible to you.

You cannot create a class loader or replace asecurity manager.

You cannot set the socket factory used byServerSocket or Socket

You cannot use the object substitution featuresof the serialization protocol


45/62


46/62

EJB Components on the Web

Three classes of objects in MVC architecture:

Model : This is the data and business-logiccomponent. It can serve multiple views.

View : This is the presentation component orthe user-interface component. There can bedifferent presentations of a single model.

Controller : This is the component that respondsto user input. Translates user-interface eventsinto changes to the model and defines the waythe user-interface reacts to those events.


47/62

Implementation of MVC in a web site

Controller

Model

Browser

Client

view1.jsp

view2.jsp

view3.jsp

Main.jsp

Views1

2

3

4

5


48/62

Design of the EJB Tier

UML use cases: UML is the UnifiedModeling Language, the standard

language for expressing the model of thesoftware system that we intend to build.

Use cases are subset of UML that

expresses the functionality of the softwareto be delivered. Use cases describe whatto do, but not how to do it.


49/62

Analysis Objects

Interface Objects : The interface object isresponsible for controlling access to the

EJB tier from any client. An interfaceobject should always be represented by asession bean in the implementation.

Ex : controller servlet for the webapplications model-view-controllerarchitecture.


50/62

Control Objects

Control objects provide services to theapplication. They model functionality that

is not naturally associated with aparticular entity or interface. Controlobjects should be represented by sessionbeans in the implementation.


51/62

Entity Objects

Entity objects model those businessobjects that should maintain their state

after the use case completes. This meansthey represent data in the database.Entity beans are often represented byentity beans in the implementation model.


52/62

An Example of EJB Design

Consider the case of a company that developsproducts, takes orders for those products, andthen manufactures and ships them.

Actors in the company : An engineer, a webcustomer, a phone operator who takes ordersfrom a catalog, floor manager who manages the

manufacturing process, a crew member thatactually builds the product ordered and a

manager who tracks overdue orders.


53/62

Use Cases

Create a Product

Place an Order

Cancel an OrderSelect an Order for Manufacture

Build a Product

Ship an Order

List Overdue Orders


54/62

Use case diagram from analysis

Engineer

Customer

Operator

Manager

Crew

Mment

Create Product

Place Order

Cancel Order

Select Order

Build Product

Ship an Order

Overdue Orders


55/62

Stereotype icons in UML

Interface Object :

Entity Object :

Control Object :


56/62

Translation of analysis model into implementation

Actor User Interface Type Interface Object Implation

Engineer Visual Basic Session Bean (RMI/IIOP)

Customer Web Application JavaBean proxy / S Bean

Operator Swing GUI Session Bean

Manager Web Application JavaBean proxy / S Bean

Crew Palm Pilot XHTML Servelet to Session BeanManagement Web Application JavaBean proxy / S Bean

View of use case actors and their


57/62

View of use case actors and theirrespective interface objects

Engineer

Customer

Operator

Manager

Crew

Manage-

-ment

VB App

Web App

Swing app

Web App

Web App

Palm App

View of interaction of interface


58/62

View of interaction of interfaceand control objects

Ship

order

Build

Product

Select

Cancel

Place

Create

List

Overdue

VB

App

Web

App

Web

App

Web

App

Swing

App

Palm

App

Vi f i t ti b t t l


59/62

View of interaction between controlobjects and entity objects

RoutingProduct

Order

Shipment

Account

Supplier

Shipping

Company

Customer

Create

Product

Place

Order

Cancel

Order

Select for

Manufacture

Build

Product

Ship

Order

List

Overdue


60/62

Summary

EJBs are intended for transactional systems

EJBs are portable, reusable server-sidecomponents that execute in a container

Assist developer productivity, extend applicationcapability, and improve system stability

Are accessible from many different types of

clientsThere are three types of beans : stateful

session, stateless session, and entity


61/62

Summary

There are four major parts to every bean: thehome interface, the remote interface, theimplementation class, and the XML deployment

descriptor

The enterprise bean developer must followcertain rules to get the benefits of EJB

technologyThe roles of EJBs can be understood by

analyzing a model of your enterprise in terms ofinterface, control and entity objects


62/62

EJB Introduction for All New Users

Documents

Transcript of EJB Introduction for All New Users