Download EJB Fundamentals

Enterprise JavaBeans:
Fundamentals
Contents
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Introduction
Technology Overview
EJB Architecture
EJB Specification
Sample Application
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Sun’s Definition
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EJB architecture is a component architecture
for the development and deployment of
component based distributed business
applications.
Applications written using EJB architecture
are scalable, transactional, and multi-user
secure.
These applications may be write once, and
then deployed on any server platform that
supports the EJB specification.
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Short Definition
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EJB is a server-side component
architecture that simplifies the process
of building enterprise-class distributed
component applications in Java.
EJB provides standard for component
architecture.
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Enterprise Bean
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Server side software components that
can be deployed in distributed multi tier
environment.
They encapsulate business logic of an
application.
Consists of one or more java objects.
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Types of Beans
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Session Bean
Entity Bean
Message driven Bean
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Session Bean
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Session beans model business
processes.
They are like ‘verbs’ because they are
actions.
E.g. billing engine, catalog engine etc:
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Entity Bean
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Entity Bean Models business data.
They are like ‘nouns’ because they are
data objects
E.g. product, an order, an employee
etc:
Session beans typically calls entity
beans to perform business goals.
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Message Driven Bean
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Message driven beans are similar to
session beans.
They are actions.
They are called only when they receive
some message.
E.g. : stock trade message.
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EJB Architecture
HTML
Client
Presentation
Tier
HTTP
Firewall
Messaging
Client
C/C++
Client
Messaging
CORBA-IIOP
Java Applet
Java Appl
RMI-IIOP
Business
Partner System
Servlet
SOAP,UDDI
WSDL,ebXML
JSP
RMI-IIOP RMI-IIOP
Application Server
EJB Message
Driven Bean
EJB Session
Bean
EJB Session
Bean
EJB Session
Bean
EJB Entity
Bean
EJB Session
Bean
EJB Fundamentals
Web
Server
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Business
Tier
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EJB Foundation: Distributed
Objects
Distributed
Object
Client
Remote Interface
Remote Interface
Skeleton
Stub
Network
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We take a monolithic application and
break it into distributed system with
multiple clients connecting to multiple
servers and databases over network.
What do we need to worry
about now?
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Services
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Remote Method
Invocation
Load Balancing
Transparent Fail Over
Back end integration.
Clustering
Dynamic Re deployment
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Object life cycle
Caching
Security
Resource Pooling
System Management
Message Oriented
Middleware
And many more…..
Middleware
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Explicit Middleware
Transaction API Transaction
Services
Distributed
Object
Client
Remote Interface
Remote
Interface
Security API
Security
Services
Database API
Database
drivers
Skeleton
Stub
Network
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Example – Bank account obj
Transfer(Acct acc1, Acct acc2,long amt)
//1.Call middleware API to perform security
check.
//2.Call middleware API to start a trans
//3.Call middleware API to load rows from db.
//4.perform trans.
//5.Call middleware API to store rows in db
//6.Call middleware API to end the trans.
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Explicit Middleware
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Difficult to Write.
Difficult to Maintain.
Difficult to Support.
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Implicit Middleware
Distributed
Client
Object
Remote
Interface
Transaction API Transaction
Request
Interceptor
Remote Interface
Remote
Interface
Skeleton
Stub
Services
Security API
Security
Services
Database API
Database
drivers
Network
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Example – Bank account obj
Transfer(Acct acc1,Acct acc2,long amt)
//1. Perform trans.(subtract bal from one
account and add to other).
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Implicit Middleware
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Easy to Write.
Easy to Maintain.
Easy to Support.
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EJB Container
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House enterprise bean and makes them
available to the client to invoke them
remotely.
It intercepts the client request and delegates
them to corresponding bean class.
It automatically performs implicit middleware
that the distributed object needs.
EJB object is the physical part of the
container.
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EJB Component Ingredients
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Enterprise Bean Class
Interfaces
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Remote and Home interface for remote
access.
Local and Local Home interface for local
access.
Deployment Descriptor.
Vendor Specific files.
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Enterprise Bean Class
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It conforms to a well defined interface.
It contains business implementation
details of our component.
Each bean type has more specific
interface that extends
javax.ejb.EnterpriseBean interface.
Bean class implements the interface
corresponding to the bean type.
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EJB Object
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Client request interceptor.
It duplicates all the business logic
methods that the corresponding bean
class exposes.
Proprietary and specific to each EJB
container.
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Remote Interface
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Interface to request interceptor.
Informs EJB Object auto generator
which methods to clone.
All remote interfaces must derive from
javax.ejb.EJBObject.
EJB remote interfaces must confirm to
RMI rules.
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Home Object
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EJB object factory.
Creates,finds and destroys EJB objects.
Proprietary and specific to each EJB
container.
Home objects implements Home
Interface.
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Home Interface
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EJB Object factory interface.
They define methods for
creating,destroying and finding EJB
Objects.
All home interfaces must extend
javax.ejb.EJBHome.
EJB remote interfaces must confirm to
RMI rules.
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Local Access
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Local objects make enterprise bean calls
fast and efficient.
 Local objects implements Local Interface.
 Local home objects creates beans fast.
 Local home object implements Local Home
interface.
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Deployment Descriptor
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Declare how the container should
perform middleware services for the
EJB component.
In EJB 2.0 deployment descriptor is a
XML file.
Key to implicit middleware.
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Vendor Specific Files
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All vendors have proprietary value
added features.
Include files specific to that vendor.
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Package
Remote
Interface
Local
Interface
Jar file creator
Enterprise
Bean
Home
Interface
Deployment
Descriptor
Vendor
Specific
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EJB jar file
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Sample Application
My First Bean!
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Session Bean : FirstBean
package example;
public class FirstBean implements javax.ejb.SessionBean{
private SessionContext ctx;
public void ejbCreate()
{
System.out.println(“ejbCreate()”);
}
public void ejbRemove() {
System.out.println(“ejbRemove()”);
}
public void ejbActivate() {
System.out.println(“ejbActivate()”);
}
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public void ejbPassivate()
{
System.out.println(“ejbPassivate()”);
}
public void setSessionContext(javax.ejb.SessionContext ctx)
{
this.ctx=ctx;
}
public String first()
{
System.out.println(“first()”);
return “My First Bean”;
}
}
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Remote Interface : First.java
package example;
public interface First extends javax.ejb.EJBObject
{
public String first() throws java.rmi.RemoteException;
}
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Home Interface : FirstHome
package example;
public interface FirstHome extends javax.ejb.EJBHome
{
First create() throws java.rmi.RemoteException,
javax.ejb.CreateException;
}
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Deployment Descriptor
<ejb-jar>
<enterprise-bean>
<session>
<ejb-name>First</ejb-name>
<home>example.FirstHome</home>
<remote>example.First</remote>
<ejb-class>example.FirstBean<ejb-class>
<session-type>Stateless</session-type>
<transaction-type>Container</transaction-type>
</session>
</enterprise-bean>
</ejb-jar>
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Client Application
package example;
import javax.naming.*;
Import java.util.*;
public class FirstClient{
public static void main(String[] arg) throws Exception{
Properties props=System.getProperties();
Context ctx=new InitialContext(props);
Object obj=ctx.llokup(“FirstHome”);
FisrtHome home=(FirstHome)
javax.rmi.RemotePortableObject.narrow
(obj,FirstHome.class);
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First first=home.create();
System.out.println(first.first());
first.remove();
}
}
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EJB Object Model
<<interface>>
java.rmi.Remote
<<interface>>
java.io.Serializable
Comes with Java2 platform
<<interface>>
javax.ejb.EJBObject
<<interface>>
Javax.ejb.EJBHome
<<interface>>
javax.ejb.EnterpriseBean
<<interface>>
javax.ejb.SessionBean
Comes with EJB Distribution
<<interface>>
Remote Interface
<<interface>>
Home Interface
Bean Implement
Class
Written by developer
EJB Object
EJB Fundamentals
Home Object
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by ComponetNCST)
Vendor Tool
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EJB Container
3: Create a new Home
EJB Object
Interface
Client
1 : Retrieve
Home object
Reference
5: Return EJB
Object Reference
2 : Return
Home object
Reference
6: Invoke Business
Method
Remote
Interface
Home
Object
4: Create a new
EJB Object
EJB
Object
Enterprise
Bean
7: Delegate Request to Bean
JNDI
Naming
Service
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Advantages of EJB
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Helps to write scalable,reliable and secure
applications.
Provides distributed component framework
and hence supports rapid application
development.
Supports application portablility and
reusability across any vendor’s enterprise
middleware services.
It is agreed upon by industry.
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References
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Mastering Enterprise Java Beans
J2EE 1.4 Tutorials
Professional Java Server Programming,
J2EE Edition
EJB Fundamentals
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