This document provides an introduction and overview of Enterprise JavaBeans (EJB) including the different types of beans, how to build a sample bean, and how to deploy and call methods on the bean. It discusses entity beans, message driven beans, and session beans. It provides code examples for a sample stateless session bean class, home and remote interfaces, deployment descriptor, and a JSP client to call methods on the bean.
Overview of EJB technology.
Enterprise Java Beans (EJB) is a server-side component technology for Java EE based systems (JEE).
Beans are business logic components that implement a standard interface through which the bean is hooked into the bean container (= runtime object for bean).
A Java class implementing one of the standard bean interfaces is an Enterprise Java Bean. Beans can be accessed remotely, usually from a client tier.
The EJB standard was developed to provide a common framework for solving recurring problems in business application development like persistence, transactions,
security and runtime and lifecycle management. The EJB standard evolved greatly over time. EJB version 1 and 2 were complex and required to implement many interfaces
and exception handling in EJBs. EJB version 3 brought great simplifications and did away with interfaces by replacing these with annotations which provide greater flexibility while keeping complexity low. EJBs come in 3 different flavors: Stateless and stateful session beans and message driven beans. Entity beans of EJB version 1 and 2 were replaced by the Java Persistence API in EJB version 3.
With the official release of Java EE 6 in December 2009 a new version of the Enterprise JavaBeans specification also saw the light. Enterprise JavaBeans is an architecture for the development and deployment of component-based business applications. Applications written using the Enterprise JavaBeans architecture are scalable, transactional, and concurrent.
While a lot of faithful EJB developer's have been scared away from the specification and some of its unfortunate implementations in the past five years, EJB 3.1 has all the ingredients that make for a successful lightweight component based implementation. At last a decent implementation of a server-side component framework as part of the Java EE specification. This no longer makes you dependent on rebel frameworks such as the Spring framework.
EJB 3.1 continues down the path where EJB 3.0 left us off. The purpose of the Enterprise JavaBeans 3.1 specification is to further simplify the EJB architecture by reducing its complexity from the developer's point of view, while also adding new functionality in response to the needs of the community. Although the Java Persistence API was developed within EJB 3.0, it now evolves under a separate JSR rather than within EJB 3.1 and will therefore not be covered in this presentation.
This presentation will mainly focus on the new features introduced by EJB 3.1 and the basics of EJB are only covered very briefly. Topics covered include: EJB Lite, simple packaging, no-interface local view, portable JNDI names, Embeddable API, Startup/shutdown callbacks, Singleton beans, the new and improved timer and scheduler component, Async invocations, and REST integration.
Overview of EJB technology.
Enterprise Java Beans (EJB) is a server-side component technology for Java EE based systems (JEE).
Beans are business logic components that implement a standard interface through which the bean is hooked into the bean container (= runtime object for bean).
A Java class implementing one of the standard bean interfaces is an Enterprise Java Bean. Beans can be accessed remotely, usually from a client tier.
The EJB standard was developed to provide a common framework for solving recurring problems in business application development like persistence, transactions,
security and runtime and lifecycle management. The EJB standard evolved greatly over time. EJB version 1 and 2 were complex and required to implement many interfaces
and exception handling in EJBs. EJB version 3 brought great simplifications and did away with interfaces by replacing these with annotations which provide greater flexibility while keeping complexity low. EJBs come in 3 different flavors: Stateless and stateful session beans and message driven beans. Entity beans of EJB version 1 and 2 were replaced by the Java Persistence API in EJB version 3.
With the official release of Java EE 6 in December 2009 a new version of the Enterprise JavaBeans specification also saw the light. Enterprise JavaBeans is an architecture for the development and deployment of component-based business applications. Applications written using the Enterprise JavaBeans architecture are scalable, transactional, and concurrent.
While a lot of faithful EJB developer's have been scared away from the specification and some of its unfortunate implementations in the past five years, EJB 3.1 has all the ingredients that make for a successful lightweight component based implementation. At last a decent implementation of a server-side component framework as part of the Java EE specification. This no longer makes you dependent on rebel frameworks such as the Spring framework.
EJB 3.1 continues down the path where EJB 3.0 left us off. The purpose of the Enterprise JavaBeans 3.1 specification is to further simplify the EJB architecture by reducing its complexity from the developer's point of view, while also adding new functionality in response to the needs of the community. Although the Java Persistence API was developed within EJB 3.0, it now evolves under a separate JSR rather than within EJB 3.1 and will therefore not be covered in this presentation.
This presentation will mainly focus on the new features introduced by EJB 3.1 and the basics of EJB are only covered very briefly. Topics covered include: EJB Lite, simple packaging, no-interface local view, portable JNDI names, Embeddable API, Startup/shutdown callbacks, Singleton beans, the new and improved timer and scheduler component, Async invocations, and REST integration.
Enterprise Java Beans (EJB) is a platform for building portable, reusable, and scalable business applications using the Java programming language.
EJB allows application developers to focus on building business logic without having to spend time on building infrastructure code for services such as transactions, security, automated persistence, and so on.
This presentation introduces EJB 3.0 concepts with code examples.
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Enterprise Java Beans (EJB) is a platform for building portable, reusable, and scalable business applications using the Java programming language.
EJB allows application developers to focus on building business logic without having to spend time on building infrastructure code for services such as transactions, security, automated persistence, and so on.
This presentation introduces EJB 3.0 concepts with code examples.
Quontra Solutions is leading provider of IT career advice, Training and consulting services for IT Professional and corporates across USA. We train individuals or Corporate via online or class Room training in all IT tools and Technologies.
We always strive to bring out innovative methods along with the traditional teaching techniques which enhance the overall experience of the students and teachers to extract the return on Investments, high efficiency and scalability.
The company’s architecture is based on the insights from the marketplace, business analytics and strategies keeping intact the fundamental principles in mind, helps us to compete and win in today’s environment without changing any quality in training.
The support, service and training provided by Quontra solutions for various customers assures a “stay up to date” easy transition from previous to current in terms of technology. Our advertisers and promoters are none other than the clients you have been associated with us for their training needs. We improve our training programs from the feedback from the students.
Email Id : info@quontrasolutions.co.uk
Website: http://www.quontrasolutions.co.uk
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J2EE is a platform-independent, Java-centric environment from Sun for developing, building and deploying Web-based enterprise applications online. The J2EE platform consists of a set of services, APIs, and protocols that provide the functionality for developing multitiered, Web-based applications.
List of topics covered during training period:
Xml, EJB,Session Beans, JSTL, Entity Beans, BMP, Transactions, Message Driven Beans, Java Mail and etc…
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These slides were used for the module "Introduction to EJB" which was taught as a part of the course "Software Engineering" for the 3rd year computer enigneering undergraduates of the University of Peradeniya in 2010.
This presentation deeply discusses the usage of EJB component in Java EE architecture. Before start reading about EJB, it is advisable to understand the history behind component-container architecture.
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2. Introduction to EJB
1. EJB provides component base Development
2. Provide write once deploy anywhere
3. Allows customization via Deployment Descriptor (no Java code
modification)
4. Development focuses on Business Logic
5. EJB Server provides
1. Transaction Mgmt
2. Security
3. Concurrency
4. Resource Mgmt
5. Messaging
6. Depoly time Customization
3. Types of Bean
1. Entity Bean
• Represent a thing in persistence store e.g. row on database or
Serialized object in file.
2. Message Driven Bean
• Can listen a message from JMS Messaging service
3. Session Bean
• Represent a process or can contain a business logic
• Stateful Session Bean
• Can remember conversational state between method call
• Stateless Session Bean
• Can’t remember conversational state between method call
4. Rules for Building a Sample Bean
To create sample bean we need to follow below steps
• Code the bean class with all business method
• Code to interfaces for bean (home & component)
• Create XML Deployment Descriptor, must be
name it as ejb-jar.xml
• Deploy bean in application server
5. Bean Class HelloBean.java
package com;
import javax.ejb.*;
public class HelloBean implements SessionBean{
public void ejbActivate(){}
public void ejbPassivate(){}
public void ejbRemove(){}
public void setSessionContext(SessionContext ctx){}
public String helloWorld(){
return "Hello there!!!";
}
public void ejbCreate() {}
}
6. Little (More) about Bean Class HelloBean.java
If you are completely new to EJB, then you definitely says
what the hec is that… here is your answers
1. Your bean class (which contains the actual definition of mth
or says business logic) must implements SessionBean
interface according to spec
2. According to java rule you have to implements all
unimplemented mth from interface
3. The helloWorld() is your actual business mth, which will be
called by client
4. The ejbCreate() not come from SessionBean interface, but
we need to give the empty definition of it (???WTF??? this
is what is going is your mind right now, b relax the answer is
coming in next few slides.
8. Little (More) about Component Interface
1. You definitely find some similarities between Component
Interface & Bean class, if you are really thinking what I m
thinking, then you are right.
2. The component interface contains declarations of all
business mth which is to be defined by Bean class.
3. But according to java rules to implement the mth from
interface, the class must have the these magical statements
“implements Interface_Name”, which is in our case is
missing. Then how these two are related. Forget this for
now, I will explain this later.
4. Component interface must extends EJBObject interface
5. Its all mth must throws RemoteException
6. They can also thorws custom application (Checked)
Exception.
7. Its return type must be primitives/Serializable
Objs/Arrays/Collection of primitives or Serializable
Objs/Remote obj (These are called as RMI-IIOP
Complients).
9. Home Interface HelloHome.java
package com;
import javax.ejb.*;
import java.rmi.*;
public interface HelloHome extends EJBHome{
public Hello create() throws
CreateException,RemoteException;
}
10. Little (More) about Component Interface
• Home interface must extends EJBHome interface
• Must declare the create() (here is hint for your Bean class
ejbCreate() mth)
• Return type of create() must be component interface type
• Mth must throws CreateException & RemoteException.
• They can also thorws custom application (Checked)
Exception.
11. Combining the all stuff together
• Now what we have here : Component, Home & bean. we know
all these stuff work together, but question is how? Here is
ur ans.
• We need to tell the container that all these things are work
together by putting their entries in ejb-jar.xml
• WTH is ejb-jar.xml? : It is Deployment Descriptor (DD) like
web.xml in servlets.
• It tells the container that which is home, component & bean
to run the business logic.
• It also states what the Bean type i.e. Session(stateless,
stateful), Entity or Message-Driven (You can understand all
this from syntax).
• We are creating only sample stateless session bean, so only
session tags are avail. For Entity & Message-Driver will see
later.
13. Deploying & Calling the Bean mth
• Now you have to create the jar of all compiled class with
below structure.
ejbApp.jar
com
Hello.class
HelloHome.class
HelloBean.class
META-INF
ejb-jar.xmlejb-jar.xml
glassfish-ejb-jar.xml
14. Deploying & Calling the Bean mth
• You noticed there is one more xml file glassfih-ejb-jar.xml,
now lets see what is it.
• As per my understanding, every server has its own ejb-
jar.xml file for deployment of ejb application. For e.g. if you
are deploying in weblogic server then you have additional
weblogic-ejb-jar.xml
• As I m using glassfish server for app deployment so I have
glassfish-ejb-jar.xml
• We will see the deployments of ejb & web application (part)
in later.
• Now I am writing the plane jsp to call the Bean mth.
• You need to deploy this jsp(war) file in glassfish & run the
jsp.
15. Client HelloClient.jsp
<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%>
<%@page import="javax.naming.InitialContext"%>
<%@page import="javax.rmi.PortableRemoteObject"%>
<%@page import="com.HelloHome"%>
<%@page import="com.Hello"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<body>
<%
try{
InitialContext ic = new InitialContext();
Object obj = ic.lookup("Hello");
HelloHome home =
(HelloHome)PortableRemoteObject.narrow(obj,HelloHome.class);
Hello hello = home.create();
String res = hello.helloWorld();
System.out.println(res);
out.println(res);
}catch(Exception e){
e.printStackTrace();
}
%>
</body>
</html>
16. Thank you
• I am not expert in EJB, but if you have any doubts in
tutorial please feel free to contact me on
ashishkirpan@gmail.com
• Sorry for spelling & grammar mistakes :)
Have a fun with EJB