T1S2_EJB_XP_01

Creating an Enterprise JavaBean

©NIIT Enterprise JavaBeans/Lesson 1/Slide 1 of 33

ObjectivesIn this lesson, you will learn to:

Identify the EJB components

Create an Enterprise JavaBean



Introduction In a multitier architecture, the client contacts a layer called

middleware The middleware instantiates and manages the server

objects The low-level services such as thread handling, security,

and transaction management are handled by the middleware

Some examples of middleware are ORB, Transaction Processing Monitor (TPM), and Component Transaction Monitor (CTM)

CTM is a hybrid of TPM and ORB Enterprise JavaBeans (EJB) is a Sun Microsystem venture

into server-side component architecture



Introduction Enterprise JavaBeans are interprocess components unlike

JavaBeans, which are intraprocess components

EJB is a specification for creating server-side components

EJB Enables and simplifies the task of creating distributed objects

EJB components are Server-side components written using Java

EJB components implement the business logic only

EJB can maintain state information across various method calls



Enterprise JavaBeans Component ArchitectureConsists of:

EJB server

EJB container

Enterprise bean



Enterprise JavaBeans Component Architecture (Contd.)EJB component architecture



Enterprise JavaBeans Component Architecture (Contd.)EJB Server:

Contains the EJB container

Provides the following services to the container:

Instance passivation

Instance pooling

Database connection pooling

Precached instances



Enterprise JavaBeans Component Architecture (Contd.)EJB Container:

Contains the enterprise beans

Clients communicate with the enterprise bean through remote and home interfaces

Provides the following services:

Security

Transaction management

Persistence

Life cycle management



Enterprise JavaBeans Component Architecture (Contd.)Enterprise Bean:Consists of methods that implement the business logicAre of two types:

Entity bean: Are enterprise beans that persist across multiple

sessions and multiple clients Are of two types:

Bean-managed persistence Container-managed persistence



Enterprise JavaBeans Component Architecture (Contd.)

Session bean: Perform business tasks without having a

persistent storage mechanism Are of two types:

Stateful session bean Stateless session bean



Just a Minute… Jane is creating an application for a departmental

store. She needs to create an application that would accept the price and would calculate the sales tax. Identify the type of enterprise bean that can be created.



Life Cycle of a Stateless Session Bean Life cycle of stateless session bean:

Does Not Exist

Method - Ready

newInstance()setSessionContext()ejbCreate()

ejbRemove()



Problem Statement 1.D.1 Earnest bank wants the development team to develop

a calculator component to convert Dollars to Rupees. Justify the choice of EJB to create the component and specify the code that has to be written.



Task List Identify the mechanism

Identify the type of enterprise bean to be created

Identify the code to be written

Write the code for the remote interface and save the file

Write the code for the home interface and save the file

Write the code for the enterprise bean class and save the file

Compile source files



Task 1: Identify the mechanism EJB is the appropriate technology since:

EJB components automatically handle system level services

Enterprise bean implements the business logic only



Task 2: Identify the type of enterprise bean to be createdCreate a stateless session bean for the banking

application



Task 3: Identify the code to be written The enterprise bean consists of:

Remote interface

Home interface

EJB class



Task 3: Identify the code to be written (Contd.)Remote Interface:

Defines all the business methods of the enterprise bean

Steps to write the remote interface:

Import the javax.ejb.EJBObject and java.rmi.RemoteException interfaces

Then, create a remote interface by extending the EJBObject interface

Finally, define all the business methods that will be implemented in the EJB class



Task 3: Identify the code to be written (Contd.)Home Interface:

Defines method that allow EJB clients to create and find EJB components

Steps to write the home interface:

Import the following interfaces: java.io.Serializable java.rmi.RemoteException

javax.ejb.CreateException

javax.ejb.EJBHome



Task 3: Identify the code to be written (Contd.) Then, create a home interface by extending the EJBHome interface

Finally, define the create() method to create an instance of a particular EJB object



Task 3: Identify the code to be written (Contd.)EJB Class:

Implements all the business methods declared in the remote interface

Steps to write the EJB class:

Import the following interfaces: java.rmi.RemoteException javax.ejb.SessionBean

javax.ejb.SessionContext



Task 3: Identify the code to be written (Contd.) Next, create the EJB class by implementing the SessionBean interface

Then, implement the business method defined in the remote interface

Finally, write the ejbCreate(), ejbRemove(), ejbActivate(), ejbPassivate(), setSessionContext(), and the default implementation for the constructor methods



Task 3: Identify the code to be written (Contd.) To create the enterprise bean called Calculator,

create the following files:

Calculator.java containing code for the remote interface

CalculatorHome.java containing code for the home interface

CalculatorEJB.java containing code for the EJB class



Just a Minute…//The remote interface

import javax.ejb.EJBObject;

import java.rmi.RemoteException;

public interface myRemote extends EJBObject

{

public int mymethod(int i);

}

What is wrong in the above code?



Task 4: Write the code for the remote interface and save the file



Task 5: Write the code for the home interface and save the file



Task 6: Write the code for the enterprise bean class and save the file



Task 7: Compile source files



Problem Statement 1.P.1 Earnest Bank wants an application that would help

their customers to view the rates of various currencies. Create an application to display the USD, Euro, GBP, and AED rates.



SummaryIn this lesson, you learned that:

Middleware handles all low-level services such as thread handling, security, and transaction management

ORB, TPM, and CTM are examples of middleware

EJB is a specification for creating server-side enterprise components that enables and simplifies the task of creating distributed objects

The EJB components are:

EJB server, which contains the EJB container



Summary (Contd.) EJB container, which contains the enterprise

beans

Enterprise bean, which contains methods that implement business logic

EJB server provides some low-level services, such as network connectivity, threads, memory, and database connections to the container

Instance passivation is a process where the EJB container temporarily swaps out a bean if it requires a resource



Summary (Contd.) Clients communicate to the enterprise bean through the

remote and home interfaces provided by the EJB container

Access control list, which is a list of user groups or persons authorized to access a particular functionality, is used to ensure security

Persistence means that a state of an object is permanently stored in a data store, such as database

The two types of enterprise beans are:

Entity beans

Session beans



Summary (Contd.) Entity beans are enterprise beans that persist across

multiple sessions and multiple clients

The two types of entity beans are:

Bean-managed persistence

Container-managed persistence

Session beans perform business tasks without having a persistent storage mechanism, such as database

The two types of session beans are:

Stateful session bean

Stateless session bean



Summary (Contd.) Remote interface defines all the business methods of

the enterprise bean

Home interface defines methods that create and look up for EJB components

The EJB class implements the business methods defined in the remote interface

T1S2_EJB_XP_01

Documents

enterprise javabeanjust

type of enterprise bean

enterprise bean class

enterprise bean steps

writtenthe enterprise

orb enterprise javabeans

enterprise javabeanlife

enterprise beans clients