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Session Beans and Business Logic

Presented By:Sethu Ram Kettimuthu

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For Starters..

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A look at the ‘Forest’ What is a middle ware?

Middleware is a layer of software between the network and the applications that provides services such as identification, authentication, authorization, directories, and security.

By promoting standardization and interoperability, middleware will make advanced network applications much easier to use.

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Trees of the ForestCORBA

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Corba (Contd) The CORBA specification only defines a set of

conventions and protocols that must be followed by CORBA implementations

CORBA does not make any restrictions on language or underlying operating system

Because of CORBA's heterogeneous nature, a neutral language was needed to perform the task of defining the interfaces to ORB-based objects

You can implement IDL interfaces using any programming language for which an IDL mapping is available

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E-Speak Fundamentally e-speak is a distributed

development environment, just like Java/RMI, just like CORBA, just like the Web itself

To access a service, a client: Creates a connection to the e-Speak engine  Identifies a contract and vocabulary to use when

searching for services  Locates the service using ESServiceFinder  Invokes the methods specified by the service

interface 

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.Net & Com+ With .NET—Microsoft's new Web services

platform—your applications, services, and devices work together to provide access to the information you need at anytime and any place

.net is MS equivalent of J2EE Com+ is MS equivalent of EJB C# is MS equivalent of Java

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Now to EJB..at lastWhy EJB?EJB enables rapid development of mission-critical application that are versatile, reusable and portable across middleware while protecting IT investment and preventing vendor lock-in

What is EJB?Enterprise beans are server components written in the Java programming language. Enterprise beans contain the business logic for your application.

For example, a checkbook client might invoke the debit and credit methods of an account enterprise bean

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Feature EJB COM+

Component Language Java only All (Java: unclear future)

Platforms All Windows 2000

Middleware Vendors 30+ Microsoft

Legacy Integration RMI/JNI, CORBA, Connectors (future)

COM TI, MSMQ, OLE DB

Protocol Any (future: IIOP) DCOM

Stateless components Yes Yes

Stateful components Yes No

Persistent components Yes No

Queued components No Yes

Middleware comes with OS

No Yes

Cluster-wide processors

Theoretically unlimited Theoretically unlimited

Development tools Choice of many Microsoft Dev Studio

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key features of the EJB technology

EJB components are server-side components written entirely in the Java programming language

EJB components contain business logic only System-level services are automatically managed for the

EJB component by the EJB server

EJB components are fully portable across any EJB server and any OS

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Types of enterprise beans Session Beans (More on Session Beans rest of the seminar)

Entity Beans- An entity bean represents a business object in a persistent storage mechanism such as a database- May be shared by multiple clients- Persistent - even when the EJB container terminates, the entity state remains in a database.

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Session Beans

Purpose : Performs a task for a client

Shared Access : May have one client

Persistence : Not persistent. When the client terminates its session bean is no

longer available.

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Session Beans – Contd.. The client accesses remote services by invoking

the session bean's methods. The session bean performs work for its client,

shielding the client from complexity by executing business tasks inside the server

It is similar to an interactive session The Session Beans Terminates with the client Session beans are powerful because they

extend the reach of your clients into remote servers-- yet they're easy to build

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How to Write Session Beans To write a session enterprise bean class, the

class must implement the javax.ejb.SessionBeaninterface

The javax.ejb.SessionBean interface extends the more generic javax.ejb.Enterprise Bean interface

So does the javax.ejb.EntityBean

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Methods in SessionBean Interface Javax.ejb.SessionBean Interface

Public interface javax.ejb.SessionBean extends javax.ejb.EnterpriseBean{

public abstract void setSessionContext(SessionContext ctx)throws java.rmi.RemoteException;

public abstract void ejbPassivate() throws java.rmi.RemoteException;

public abstract void ejbActivate() throws java.rmi.RemoteException;

public abstract void ejbRemove() throws java.rmi.RemoteException;}

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A look at each method setSessionContext(SessionContext ctx)

Container calls this method to associate the bean with a session context

A session context is the bean’s gateway to interact with the container

The bean can use the session contexts to query the container about the current transactional state,security state etc..

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A look at each method ejbCreate(..)

Initializes the session bean Can define one or more ejbCreate() methods and

each can take different arguments Can perform any initialization the bean needs,ie.,

public class MyBean implements SessionBean {private int memberVar;

public void ejbCreate(int init val) {this.memberVar = initval;

}…. }

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A look at each method ejbPassivate() If too many beans are instantiated, the EJB

container can passivate some of them(by writing the beans to a temp storage like a DB or File)

The container can then release the Resources the beans had claimed

Immediately before the Beans are passivated the container calls the ejbPassivate() method

NOTE: Remember that passivation doesn’t apply to stateless bean as it cannot hold the state.

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A look at each method ejbActivate() When a client needs to use the passivated bean

then the container ‘kicks’ the bean back into memory. This is activation.

Once the bean is back in the memory again , the beans implementation acquires any resource the bean needs.

NOTE: Activation doesn’t apply to stateless session beans as it cannot hold state and can simply be created/destroyed rather than passivated/activated

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Guess who spoke this "You've heard Al Gore say he invented the

internet. Well, if he was so smart, why do all the addresses begin with "W"?“

Any body …?

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A look at each method ejbRemove()

When the container is about to remove your session bean instance it calls the bean’s ejbRemove() method

ejbRemove is a clean-up method, alerting the bean that it is about to destroyed.

ejbRemove() is a required method of all beans and takes no parametrs.

There is only one ejbRemove() method per bean.

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A look at each method Business Methods: There can be zero or more Business methods in

your bean These methods actually solve business problems

For eg:public class MyBean implements SessionBean {

public int add(int I,int j) {return(I + j) ;}

…} For clients to call your business methods, the

business methods must be listed in the bean’s remote interface

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Major parts of an EJB Application

Session Bean Class Home Interface Remote Interface Deployment Descriptor

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Two types of State Transactional state

Roughly speaking this is the data stored in the persistent store

Multiple client can read and modify the data without conflict

If the App Server crashes or re-started the data is still available in the data store

Example: An order that a customer has placed

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Two types of State Conversational State :

Cached data either on the Client or Server Private data that isn’t accessible to other clients Example : The web shopping cart before the order

has been confirmed REMEMBER: A stateless session bean holds

conversations that span a single method call.So it doesn’t hold Conversational state, BUTstateful session bean holds Conversational state

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Types of Session Beans

Stateless Session Beans

Stateful Session Beans (We’ll see about this later)

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Stateless Session Beans(SLSB) A stateless session bean does not maintain a

conversational state for a particular client When a client invokes the method of a stateless

bean, the bean's instance variables may contain a state, but only for the duration of the invocation

The state is not customized for each client The SLSB cannot retain state between method

calls,but they also cannot retain state after a client passes data to an ejbCreate() call

So all SLSB may expose only a single ejbCreate()method,which takes no parameters

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Stateless Session Bean Pooling

Client

Remote Interface

EJB Obj bean

bean

bean

Stateless session bean pool

Invoke()

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‘Hello world’ SLSB Function:

The SLSB, a component running in a Distributed Environment will do the mighty task of returning the string ‘Hello World’ to the client.

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‘Hello world’ Remote Interface The remote interface is what the clients operate

on when they interact with EJB objects. The container vendor will implement this interface; the implemented object is the EJB object,which delegates invocations to the actual bean

import javax.ejb.*; import java.rmi.RemoteException; Import java.rmi.remote;

Public interface Hello extends EJBObject {public String hello() throws

java.rmi.RemoteException;}

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Implementing the ‘Hello world’ bean/* Stateless Session bean */

import javax.ejb.*;public class HelloBean implements SessionBean {/* EJB required methods */public void ejbCreate( ) { System.out.println(“Create Method”);}

public void ejbremove( ) { System.out.println(“Remove Method”);}public void setSessionContext(SessionContext ctx){ System.out.println(“Set Session Context”); }

// Business Methodspublic String hello() { System.out.println(“Hello()”);return “Hello World”; }}

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‘Hello World’ Home Interface The Home Interface for HelloBean is implemented

by the EJB Server’s glue-code tools- the implemented object is called the Home Object and serves as the factory for EJB Objects

import javax.ejb.*;import java.rmi.RemoteException;/* One create() method is in this Home INTERFACE */public interface HelloHome extends EJBHome {/* This method creates the EJB Object & return the newly created EJB object*/

Hello create() throws RemoteException, CreateException;}

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Deployment DescriptorDeployment Descriptor Setting Value

Bean Home Name HelloHome

Enterprise bean class name .helloworld.HelloBean

Home Interface Class name .helloworld.HelloHome

Remote Interface class name .helloworld.Hello

Environment Variables <empty>

Re-entrant false

Stateful or stateless STATELESS_SESSION

Session timeout 7 secs

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EJB-JAR File Last step before deploying Package all the files above in an EJB-Jar file Jar files are compact modules in which to wrap our

beans The files to be included are :

Enterprise Bean Remote Interface Home interface Deployment Descriptor

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Client pseudo-code for Stateless Bean The HelloClient class invokes methods on a simple stateless beans Get system properties for JNDI initialization Form an initial context Get a reference for the home object(factory for EJB Objects) Use the factory to create EJB Object Call the Hello() method and print the string Since the EJB object is done with, remove it /* hello.remove; */ Check for any Exception

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Lifecycle of a SLSBBecause a stateless session bean is never passivated, its life cycle has just two stages: non-existent and ready for the invocation of business methods.

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Stateful Session Beans

Stateful Session Beans are conversational beansBecause they hold conversation with clients that span multiple method invocations

Stateful Session Bean store conversatinal state within the bean

The conversational state is specific to a particular client

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Passivation of Stateful bean

Remote Interface

EJB Obj bean

bean

bean

Client

Passivated Bean stored

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Stateful Session bean Lifecycle

Does not exist

Ready PassiveejbPassivat

e

ejbActivate

2. ejbRemobe1.remove

1.create2.

setSessionContext3 ejbCreate

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CartEJB.javaimport java.util.*;import javax.ejb.*; public class CartEJB implements SessionBean {  String customerName; String customerId; Vector contents;  public void ejbCreate(String person) throws CreateException {  if (person == null) { throw new CreateException("Null person not allowed."); } else { customerName = person; }  customerId = "0"; contents = new Vector(); }

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public void ejbCreate(String person, String id) throws CreateException {  if (person == null) { throw new CreateException("Null person not allowed."); } else { customerName = person; }  IdVerifier idChecker = new IdVerifier(); if (idChecker.validate(id)) { customerId = id; } else { throw new CreateException("Invalid id: " + id); }  contents = new Vector(); }

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public void addBook(String title) {  contents.addElement(title); } public void removeBook(String title) throws BookException {  boolean result = contents.removeElement(title); if (result == false) { throw new BookException(title + " not in cart."); } } public Vector getContents() { return contents; } public CartEJB() {} public void ejbRemove() {} public void ejbActivate() {} public void ejbPassivate() {} public void setSessionContext(SessionContext sc) {} }

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The SessionBean Interface

The SessionBean interface extends the EnterpriseBean interface, which in turn extends the Serializable interface. The SessionBean interface declares the ejbRemove, ejbActivate, ejbPassivate, and setSessionContext methods

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The ejbCreate MethodsBecause an enterprise bean runs inside an EJB container, aclient cannot directly instantiate the bean. Only the EJB

container can instantiate an enterprise bean. During instantiation, the example program performs these steps:

1. The client invokes a create method on the home object: Cart shoppingCart = home.create(“Sethu","123");

2. The EJB container instantiates the enterprise bean. 3. The EJB container invokes the appropriate ejbCreate method in CartEJB

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public void ejbCreate(String person, String id) throws CreateException {  if (person == null) { throw new CreateException("Null person not allowed."); } else { customerName = person; }  IdVerifier idChecker = new IdVerifier(); if (idChecker.validate(id)) { customerId = id; } else { throw new CreateException("Invalid id: " + id); }  contents = new Vector(); }

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Business MethodsThe primary purpose of a session bean is to run business tasks for the client. The client invokes business methods on the remote object reference that is returned by the create method. From the client's perspective, the business methods appear to run locally, but they actually run remotely in the session bean. The following code snippet shows how the CartClient program invokes the business methods:

Cart shoppingCart = home.create("Duke DeEarl", "123");. . .shoppingCart.addBook("The Martian Chronicles"); shoppingCart.removeBook("Alice In Wonderland");bookList = shoppingCart.getContents();

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The CartEJB class implements the business methods in the following code:

public void addBook(String title) { contents.addElement(new String(title));}public void removeBook(String title) throws BookException { boolean result = contents.removeElement(title); if (result == false) { throw new BookException(title + " not in cart."); }}public Vector getContents() { return contents;}

 

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Home InterfaceA home interface extends the EJBHome interface. The purpose of the home interface is to define the create methods that a client may invoke. The CartClient program, for example, invokes this create method:

Cart shoppingCart = home.create("Duke DeEarl", "123");

Every create method in the home interface corresponds to an ejbCreate method in the bean class. The signatures of the ejbCreate methods in the CartEJB class follow: public void ejbCreate(String person) throws CreateException . . . public void ejbCreate(String person, String id) throws CreateException

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create methods in the CartHome interface:

import java.io.Serializable;import java.rmi.RemoteException;import javax.ejb.CreateException;import javax.ejb.EJBHome; public interface CartHome extends EJBHome { Cart create(String person) throws RemoteException, CreateException; Cart create(String person, String id) throws RemoteException, CreateException; }

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Remote InterfaceThe remote interface, which extends javax.ejb.EJBObject, defines the business methods that a client may invoke. Here is the source code for the Cart remote interface :

import java.util.*;import javax.ejb.EJBObject;import java.rmi.RemoteException; public interface Cart extends EJBObject { public void addBook(String title) throws RemoteException; public void removeBook(String title) throws BookException, RemoteException; public Vector getContents() throws RemoteException;}

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You should consider using a stateful session bean if any of the following conditions are true: •The bean's state must be initialized when it is created.

•The bean needs to hold information about the client across method invocations.

•The client is an interactive application.Since the primary goal of a session bean is to represent a client in the J2EE server, most of your session beans will be stateful. However, sometimes you may want to use stateless session beans:

•The bean performs a task that is not tailored to the needs of a particular client. For example, you might use a stateless session bean to fetch from a database a commonly used set of data.The bean doesn't need to hold information about the client across method invocation

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FIRE ……….

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Am Still Alive !!!!

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ReferencesOn Starters :www.calvinandhobbes.comMore on ‘HIS’ Quotes:www.bushisms.comMore on EJB:????????????Ask Google or Dr. juggy Actually > 1) Text: Mastering EJB by Ed roman

2) www.javaworld.com 3) http://java.sun.com/products/ejb/

4) http://theserverside.com/home/index.jsp