Ejb Overview

7/31/2019 Ejb Overview

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Enterprise JavaBeansFundamentals


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Agenda

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Enterprise JavaBeans defined

EJB and Distributed Computing

EJB Architecture

Entity beans Session bean

Deployment

EJB Clients


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Enterprise JavaBeans: Defined


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What is Enterprise JavaBeans

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component architecture for the development and deployment of

object-oriented distributed enterprise-level applications

Scalable

transactional

multi-user secure

collection of Java classes and XML file, bundled into a single

unit. The Java classes must follow certain rules and provide

certain callback methods.


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In English Please!

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Enterprise JavaBeans is a specification (a piece of paper) not a product

As is XML, CORBA, TCP/IP

Enterprise JavaBeans is Java based Defined by Sun Microsystems

Applications are written in Java

Enterprise JavaBeans is distributed objects Similar to CORBA | Java RMI (JRMP) | Microsoft MTS

Enterprise JavaBeans is components Similar to regular JavaBeans (similar but not the same)

Similar to COM/DCOM/COM+

Enterprise JavaBeans products are TransactionalMonitors Similar to CICS | TUXEDO

A complete environment for a distributed object


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Enterprise JavaBeans

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Simple Programming Model Attribute based programming

Focus on Business Logic

Simple API

Well defined Lifecycle

Portable

Specification ensures basic services

Component Packaging (JARs and XML DD)

Java


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WORA

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Write-Once, Run Anywhere within Middleware

Middleware provides all services

Instance management, transactions, concurrency,persistence

Beans stay simple!


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EJB Advantages

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With EJB, you can write a business object andeasily make it

Persistent

Distributed

Transactional

Secure

Multithreaded


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Persistent

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Beans need to load and store data

You can let the server do it

(Container-Managed Persistence)

You can do it yourself (Bean-Managed Persistence)


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Transactional

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Support for distributed transactions

You can let the Server manage all transactions

You will if you know whats good for you

You can give it hints in deployment descriptor


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Secure

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SSL/RMI protects transmitted data

Client-Server architecture protects

proprietary code

backend database

SSL authenicates client, server

ACLs provide fine-grained control of access toobjects, methods, services


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Multithreaded

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Programmer delegates all responsibility formultithreading to server

Programmer literally cant spawn a thread

Program designer and/or sysadmin establishesmultithreading policies

Server enforces them invisibly


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Naming Services

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JNDI

Wrapper for many naming services

CORBA, RMI, etc.


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CORBA and EJB

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Transport EJB uses RMI interface, RMI uses IIOP

CORBA 3.0 promises object compatibility with

EJB

Not quite sure what that means

Some EJB Servers contain an ORB

All EJB Objects are also CORBA objects


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EJB Architecture


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EJB Roles

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Bean developer:creates JAR with: Remote interface with business functions

Home for accessing instances of bean

Bean itself

Properties and descriptor

Assembler:one who combine the EJBcomponents with other software to make acomplete application

Deployer:modifies and deploys beans in EJBserver

Organization-specifics, ie security


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EJB Roles (cont.)

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Server providerprovides Server run-time Container provider:provides tools and containers

Creates container classes that wrap bean

Manage installed beans

System administrator- one who manages theapplication after it has been deployed into a targetenvironment.


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The EJB Container

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Think of the container as the server, holding yourobjects

Containers host enterprise beans

Containers isolate beans from clients

Intercept client requests

Set up transactions, security, persistence, etc.before and after calling EJB methods

Beans can also call methods of the containerinterface to get services

Containers provide JNDI services too


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EJBProvider

ApplicationAssembler

App Server/EJB Container

Provider

Deployer

System

Administrator


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Session Beans

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Not persistent, but can access database Model tasks, process or agents

Charge a credit card

Process a stock purchase

Perform hotel reservations Manage interactions of other beans


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Stateless Session Beans

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Perform transitive tasks Independent business methods

Act on method arguments, not bean state

Similar to procedures in traditional TPM systems

Most performant bean type

Not dedicated to one client


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Stateful Session Beans

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Act on behalf of one client Extension of the client

Agent that performs work for the client

Interdependent business methods

Bean has conversational state

Method depend on conversational state

Dedicated to exactly one client


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EJB Conversation

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Finding the Bean Getting access to a bean

Calling the beans methods

Getting rid of the bean


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Finding the bean

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Use naming service (associates a symbolic namewith an object)

Use JNDI to provide a uniform interface to allnaming services or CORBAs COS

Naming Services

DNS

UNIX /etc/hosts file system


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Getting access to bean

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Naming lookup returns reference to homeinterface object

Client uses the home interface to find existing EJBinstances or create new one.

Look up returns reference to remote Interface

object

Client uses remote interface to interact with EJBobjects


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Calling the bean and getting rid of it

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Invoke the public methods of bean Destroying by remove()

Stateful session container discard it and use thespace for other bean

Stateless session returns the instance to a pool Entity remove the underlying object from

persistent storage ie. database


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Building and deploying EJBs


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Building and deploying EJBs

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Writing the EJB EJB implementation class Home interface Remote interface Deployment descriptor Properties file containing any environment properties that a bean

expects Create a manifest file for creating the ejb-jar file (medium to

distribute EJBs)

Deploying EJB Ejb container reads the ejb-jar file Create implementations for the home & remote interfaces

Read the deployment descriptor Add the beans property settings to the environment

Connecting to the EJB Either RMI or CORBA to connect to the EJB

Function of a Deployment


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Function of a DeploymentDescriptor

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Describe bean(s) to the container interfaces and class

type of bean (entity or session)

identify primary key & container-managed fields

Declare runtime behavior transaction attributes of methods

authorization access to method

persistence type (BMP vs. CMP)

Written in XML


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Deployment Descriptor

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Name of the EJB class Name of the EJB home interface

Name of the EJB remote interface

ACLs of entities authorized to use each class ormethod

For Entity beans, a list of container-managedfields

For session beans, a value denoting stateful orstateless

Programming: Interfaces and


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g gClasses

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Home Interface (1) Extends javax.ejb.EJBHome

Provides remote access to create, find, remove beans

Remote Interface (2)

Extends javax.ejb.EJBObject Provides remote access to business methods

Bean Class EJB Implementation class (3) Extends a javax.ejb.EnterpriseBean type

Implements business logic and other functionality

EJB Architecture


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EJB Architecture

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Implements

Invokes

Creates / uses

Client

Server

Home Interface(Factory)

EJB Object

(Wrapper) Enterprise

Java Bean

(Biz Logic)

Remote

Interface

Container

RMIRMI

Naming Service

You write this

Bean provider: What to write?


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Bean provider: What to write?Eg. Stateless Session Bean

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Remote Interface

extend EJBObject interface

Define business method signatures

Home Interface extend EJBHome interface

Define create signatures

May define findBy signatures for entities


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Remote Interface

import javax.ejb.EJBObject;

import java.rmi.RemoteException;

public interface Customerextends EJBObject {

public String getName(String n) throws RemoteException;

}

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Functionality of remote interface

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Container generates a class implementingCustomer interface during deployment time

The class passes method invocations to the EJBimplementation class

Allows the client to do: Get a reference to the beans home interface (thru

getEJBHome() method)

Get a reference that can be saved and then

restored (thru getHandle() method) Get rid of the objet (thru remove() method)

Test whether two remote objects are identical(isIdentical())

Home Interface


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Home Interface

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import javax.ejb.EJBHome;

import javax.ejb.CreateException;

import javax.ejb.FinderException;


public interface CustomerHome extends EJBHome {

public Customercreate()throws RemoteException,CreateException;

}


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Functionality of Home interface

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Create() Atleast one create method should be there

replace constructors in EJB for initializing an object

Initialize the internal state of the object where

container maintain a cache of already instantiatedobjects

Stateless only one create() with no arguments

Must be public

Return type must be the type of the remoteinterface

Throws clause must include RemoteException andCreateException


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Other method signature of Home interface

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remove() allow a client to delete EJB instances byits handle or its primary key

getEJBMetaData returns an object the

implements the EJBMetaData

Bean implementation:What to write


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Bean implementation:What to write(cont.)?

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Enterprise Bean Class

implement EntityBean or SessionBean

Implement business method signatures

Does not need to implement Remote Interface

not abstract

Implement ejbCreate methods matching Homecreate One ejbCreate for every Home.create

N.B.: create in home interface, ejbCreate in Bean

Bean Class


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import javax.ejb.*;

public class CustomerBean implements SessionBean

{

SessionContext ctx;

public void ejbCreate() { }

public Name getName(String n)

{return How are you, + n;

}

public void ejbRemove() { }

public void ejbPassivate() { }public void ejbActivate() { }

public void setSessionContext(SessionContext ctx)

{ this.ctx = ctx;}

}

Session bean method signatures


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ejbActivate() -called by container after sessionbeans state has been restored from semi-persistent storage

ejbPassivate() called by container beforeswapping the object out to semi persistent storage

ejbRemove() invoked as result of client callingthe remove()

setSessionContext()

Container passes context object to session bean atthe very beginning of beans life

Bean stores this object in an object variable

Use this to interact with container provided services

like security & transaction management



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ejbCreate()

Public

Void return type

Number and type of arguments of ejbCreate() mustsame as the number and type of arguments in thecreate() method

No need of throwing exceptions bcos exceptions

are thrown from create() method

g


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Compile (4)Remote Interface

Home InterfaceImplementation class


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Create a session descriptor (5)

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SessionDescriptor class Specifies the deployment environment

Deployer deserializes the instance of Sessiondescriptor and uses the information it contains to

deploy the bean


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import javax.ejb.deployment.*;;

import java.io.*;

import java.util.Properties;Public class DDWrite

{

public static void main(String argv[])

{

SessionDescriptor sd = new SessionDescriptor();sd.setEnterpriseBeanClassName(Customer);

sd.setHomeInterfaceClassName(CustomerHome);

sd.setRemoteInterfaceClassName(CustomerRemote);

Properties p = new Properties();

p.put(myprop1, myval0;sd.setEnvironmentProperties(p);

sd.setSessionTimeout(0);

contd

sd setStateManagementType(SessionDescriptor STATEL


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sd.setStateManagementType(SessionDescriptor.STATELESS_SESSION)

try {

FileOutputStream fos = new FileOutputStream(foo.ser);

ObjectOutputStream oos = new ObjectOutputStream(fos);

oos.writeObject(sd);

oos.close();}

catch (IOException ioe)

{

}

}}

Foo.ser serialized deployment descriptor

WriteOBject () performs actual serialization

Create a manifest (6)&ejb-jar(7)


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&Deployment (8)

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Contains information about the contents of a jarfile

Name:directory/ CustomerBeanDD.ser

Enterprise-Bean: True

Create an ejb-jar file with

jar cmf (manifest file name) (name of the jar)(thedirectory to include in the jar file

Deployment with deployment tool

Writing a client(9)Run the client according


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import project directory;

import java.rmi.*;

import javax.naming.*;Public class HelloClient

{ public static void main(String argv[])

{ try {

InitialContext ic = new InitialContext();

CustomerHome home= (CustomerHome) ic.lookup(CustomerHome);Customer cust = home.create();

String name = cust.getName(Suriya);

S.O.P. (returned + name);

cust.remove();

} catch (java.rmi.RemoteException e) { }catch (javax.ejb.CreateException e) {}

catch (javax.ejb.RemoveException e) {}

catch (javax.naming.NamingException e) {}} }

Run the client according

to the webserver

launched

Home Interface


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o e te ace

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Defined by Bean developer Implemented by server tools (autogenerated)

Must extend interface EJBHome

EJBMetaData getEJBMetaData()

void remove(Handle ejbHandle)

void remove(Object primaryKey)

Must provide your own create() methods

Foo create()

Foo create(Bar b, Baz z)

Home Interface: Entity Beans


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y

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Entity Beans are persistent, therefore they needmore than a create method

Need findXXX methods

public Foo findByPrimaryKey(Object key);

public Foo findByBar(Bar bar); public Enumeration findOverdrawnAccounts();

Implement ejbFindXXX methods in bean

N.B.: find in home interface, ejbFind in Bean

Remote Interface


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Written by developer Defines methods accessible by client

Your business methods go here

extends javax.ejb.EJBObject

standard methods provided by all EJBs

getEJBHome(), getPrimaryKey(), getHandle(),remove(), isIdentical(EJBObject obj)

Interfaces and Implementations


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p

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EJBObjectgetEJBHome()getPrimaryKey()

getHandle()isIdentical()

remove()deposit()

getBalance()

Remote Interface

deposit()getBalance()

EJBejbCreate()

ejbRemove()ejbActivate()

ejbPassivate()deposit()getBalance()

Home Interface

create()remove()


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Beans and Persistence

P i t


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Persistence

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Container-Managed Persistence Server reads values from your bean

Server stores/loads data for you

Very easy to write - just define data and server

magically takes care of persistence

Container-Managed Persistence(CMP)


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(CMP)

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Persistence is automatic inserts, updates, and deletes are automatic

transactions managed automatically

server reads/writes your bean instance variables

Server also informs you before/after it's donesomething you implement callback methods

Container-Managed Persistence(CMP) t


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(CMP) cont.

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Easier to write beans Focus on business logic, not persistence

But, requires sophisticated, vendor-specific datamapping tools

Components more portable not backend-specific

shrink-wrapped components

Bean Managed Persistence


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Bean-Managed Persistence

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Bean-Managed Persistence You code access database directly

Callback methods dictate when to insert, update,delete

More control over persistence, performance Much harder to write

Dont need sophisticated data mapping tools

Entity Beans


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Entity Beans

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Model entities in a system represent their data and associated behavior one or many relational database tables

an object in an object database

an entity in a legacy system

Nouns: People, Places or Things Customer, Employee, Student

City, Building, Hotel Room

Order, Organization, Health Benefit

Online Resources


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Online Resources

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jGuru EJB FAQ http://www.jguru.com/faq/EJB

Sun EJB Page

http://java.sun.com/products/EJB

EJBNow http://www.ejbnow.com/

Remote Interface


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import javax.ejb.EJBObject;


public interface Customerextends EJBObject {

public String getName() throws RemoteException;public void setName(Name name) throws RemoteException;

public Address getAddress() throws RemoteException;

public void setAddress(Address address)throws RemoteException;

}

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Home Interface


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import javax.ejb.EJBHome;

import javax.ejb.CreateException;

import javax.ejb.FinderException;


public interface CustomerHome extends EJBHome {

// required in session bean also

public Customercreate(Integer customerNumber)throws RemoteException, CreateException;

//not required in session bean

public Customer findByPrimaryKey(Integer customerNumber)

throws RemoteException, FinderException;

public Enumeration findByZipCode(int zipCode)

throws RemoteException, FinderException;

}

Bean Classimport javax.ejb.EntityBean;


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public class CustomerBean implements EntityBean {

Address myAddress;Name myName;

CreditCard myCreditCard;

public Name getName() {

return myName;

}

public void setName(Name name) {

myName = name;

}

public Address getAddress() {

return myAddress;

}

public void setAddress(Address address) {

myAddress = address;

} ...

}

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