Enterprise Java Beans I

8/14/2019 Enterprise Java Beans I

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Enterprise Java Beans

CS-422


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J2EE Industry Acceptance

To be successful J2EE must have wide industry acceptance

APIs would be useless if infrastructure vendors dont implement support

for the J2EE APIs

Sun made alliances with many Industry leaders to insure the success ofJ2EE

Transaction Management

IBM, Compaq/Tandem, BEA Systems

Persistence Management

Oracle, Sybase, Informix

Directory Services

HP, Netscape, IBM


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J2EE APIs

Enterprise Java Bean (EJB) API

Java Naming and Directory Interface (JNDI)

Remote Method Invocation/Internet Inter-ORB Protocol

Java IDL

Servlets and JSP

Java Messaging Service (JMS)

Java Transaction Service JTS)

Java Transaction API (JTA) Java Database Connectivity (JDBC)


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EJB API

The EJB API defines a server component model

provides portability across application servers

implements automatic services on behalf of the application components


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JNDI API

Provides access to naming and directory services

DNS, NDS, NIS+, LDAP, COS

used to look up interfaces used to create EJBs, JDBC connections and

other things


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RMI/IIOP

Allows the creation of remote interfaces for distributed computing

default protocol (JRMP, Java Remote Method Protocol) is proprietary,

based on Javas serialization APIs

RMI-IIOP a JDK 1.3 extension of RMI that allows the use of IIOP(Internet Inter ORB Protocol) for RMI communication. J2EE Spec

requires this as the standard protocol for communications between the

different tiers of the J2EE architecture.


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Java IDL

Creates remote interfaces to support CORBA communications in the

Java platform

includes IDL compiler and a lightweight ORB

allows the integration of non-Java based components


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Servlets and JSP

Used for creation of thin client interfaces for the presentation of

information and collection of user inputs

Support the dynamic HTML generation and session management for

browser based clients


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JTA

Provides a transaction demarcation API

provides the infrastructure for transaction management

open, committ, roll back

if the transaction spans multiple beans deployed on the same server or on

widely dispersed servers, the server vendor is responsible for proper

implementation od transaction control

transactions spanning multiple servers require the propigation of

transaction context between servers over IIOP


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JTS API

Defines a distributed transaction management service based on

CORBAs Object Transaction Service


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JDBC

Provides uniform access to relational databases such as DB2, Oracle,

SQL Server and Sybase

Provides provides interfaces to RDBMs both for data definition and

query/insert/update/delete

latest version provides for database connection pooling


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Where we stand on J2EE...

In CS-328 we covered the following APIs: JDBC

RMI

JavaIDL

HTTP and the Web

JNDI

In CS-422 weve covered:

Servlets and JSP

Whats left:

JMS (to be covered in CS-328)

JTA (some day)

JTS (some day)

EJB


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What is Enterprise Java Beans

Defines a model for the development and deployment of reusable Java

server components

Components are pre-developed pieces of applications code that can be

assembled into working application systems The EJB Architecture logically extends the Java Beans component

model to support server components

Server components run in an application server

A Java application server provides an optimized execution

environment for server-side Java application components by combining traditional OLTP (On-line Transaction Processing)

technologies with a Java application server delivers a high performance,

highly scalable, robust execution environment specifically suited to

support Internet enabled application systems


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Containers

J2EE doesnt specify how a J2EE runtime should be built, but instead

provides an abstraction of the runtime infrastructure as a container

Component contract

Container Service APIs Declaritive services

Other container services

The EJB Specification defines 4 types of containers:

an applet container to run applets

an application-client containerfor running standard Java application

clients

a Web Containerfor hosting Java servlets and JSPs

anEJB Containerfor hosting Enterprise Java Beans


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J2EE Applicatiuon Server

Web Container

J2EE Container Architecture

Applet Container

Application Client

Container

EJB Container

RMI/IIOP

JNDI

JTA

JDBC

JMS

JavaMail

JAF

RMI/IIOP

JNDI

JTA

JDBC

JMS

JavaMail

JAF

Java Servlets

JSP Pages

Databases and

Other Resources

JMS

JDB

C

EJBs

App.Client

Applet


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The EJB Container

An EJB server must provide one or more EJB containers which

provide homes for the enterprise beans

The EJB container manages the beans housed in it

responsible of registering the bean

providing a remote interface for it

creating and destroying object instances

checking security

coordinate distributed trancactions

can optionally manage persistent data within the object

any number of EJB claees can be installed in a particular conrainer but

each class can only be assigned to a particular container


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EJB Container

Client

EJB Object

(Client view)

EJB Home

(bean identifier)

Enterprise Bean

Deployment

Descriptor

Environment

The EJB Object interface intercepts all method calls

and implements transactions, state management,persistence,and security services for the bean based

on deployment descriptor settings

The EJB Home interface is accessible through JNDI

and implements all lifecycle services for the bean.


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Transient and Persistent Objects

Session Beans (transient object) session beans are created and exist usually for a single user session

performs operations on behalf of the client

may be transactional but are not usually recoverable after a system crash

can be stateless or can maintain conversational state across methods and

transactions

container manages the conversational state of a session bean if it needs to

be evicted from memory

must manage its own persistent data

Entity Bean (persistent object)

an object representation of persistent data that are maintained in apermanent data store (like a database)

a primary key identifies each instance of the entity bean

are transactional and are recoverable following a system crash

Enterprise Java Beans I

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