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J2EETM : Why, What and How

University of Texas at Dallas

Anna Yi

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Objectives

• Why J2EE?

• What is J2EE?

• How to use J2EE?

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Motivation for J2EE

• Need for– New multi-tier enterprise computing model in

web environment– A way to bring in different elements of

enterprise application• Web interface design• Transaction processing• Meeting non-functional system requirements:

– Availability, reliability, enhanceability, performance, scalability, reusability, interoperability

• Timely development and deployment

Why J2EE?

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Two-tier Client/Server Architecture

Client Server

Why J2EE?

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Simple Web Client/Server• Interaction of two-tier architecture

• Client: simply accesses web pages through web browser

• Server: retrieves html documents

Why J2EE?

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CGI-based Web Client/Server

• Interaction of two-tier architecture• Client: uses service requiring 2ndary

storage• Server: manipulates forms, Database

updates, (primitive) electronic commerce• Fat Server/ Thin Client

Why J2EE?

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Java Applet-based Web Client/Server

• Interaction of two-tier architecture• Client: uses Java Applet for client-side

computation• Server: provides Applet bytecode• Fat Client/Thin Server

Why J2EE?

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Two-tier Client/Server Architecture

But what is the problem with this architecture?

Client Server

• So, important processing needs to be run on the server

• Then, Java needs to run on the server too to be more useful enterprise

• The server is almost like what CGI-programming does

• Client: data access applying business logic and presentation of data (computation)

• Server: serves only as service-database server, not application server web server

Why J2EE?

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Drawbacks of two tier application architecture

• Easy to deploy, but difficult to enhance or upgrade

• Reusability of business and presentation logic difficult

• Not scalable

Why J2EE?

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Vision of J2EE

• An open standard

• Umbrella for anything Java-related

• For designing, developing, assembling, and deploying component-based enterprise applications

• Separation of business logic from presentation

• Reusability, enhanceability, scalability, interoperability

Why J2EE?

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Separation of Business logic from Presentation logic

• Presentation logic : display• Business logic : what the company wants to do

Example: the distribution of different sales figures by diff dept (business logic) can be represented in many different ways (pie chart, bar graph, etc)

Why J2EE?

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Why J2EE?

• Simplifies the complexity of a building n-tier application

• Standardizes an API between components and application server container

• J2EE Application Server and Containers provide the framework services

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What is J2EE?

• Defines the standard for developing multitier enterprise applications

• Simplifies enterprise applications by:– Basing them on standardized, modular components– Providing a complete set of services to those

components– Handling many details of application behavior

automatically, without complex programming

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Thin-client Multi-tiered Architecture

What is J2EE?

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J2EE Tiers

• Client Presentation HTML or Java applets

deployed in Browser XML documentations

transmitted through HTTP Java clients running in

Client Java Virtual Machine (JVM)

• Presentation Logic Servlets or JavaServer

Pages running in web server

• Application Logic Enterprise JavaBeans

running in Server

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J2EE Components & Services

• Components- Java Servlets- JavaServer Pages (JSP)- Enterprise JavaBeans (EJB)

• Standard services & supporting technologies- Java database connectivity(JDBC) data access API- Java Messaging Service (JMS) (Remote Method Invocations (RMI))- Extensible Markup Languages(XML)- JavaIDL (Interface Description Language)- JavaMail- Java Security- CORBA technology- Design Patterns

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Advantages of Multi-tiers

• Tiers separate functionality:– Presentation Logic, Business Logic, Data

Schema

• Easier upgrade since one tier can be changed without changing the rest

• Lower deployment and maintenance cost• More flexible (can support changes), more

extensible (can add functionality)

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The Big PictureWhat is J2EE?

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4-Tier Model

Client TierWeb Tier

Business Tier

EIS Tier

What is J2EE?

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Commercial Platforms

• J2EE SDK 1.3 (Sun) *

• WebLogic (BEA Systems)

• WebSphere (IBM)

• iPlanet (Sun & NetScape)

• JBoss (Open source)

What is J2EE?

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What is Application Server

Application servers enable the development of multi-tiered distributed applications. They are also called “middleware”

An application server acts as the interface between the database(s), the web servers and the client browsers

What is J2EE?

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Application Server: Key Services

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JBoss- Application Server

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J2EE Components

• Java Servlets

• JavaServer Pages (JSP)

• Enterprise JavaBeans (EJB)

What is J2EE?

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Overview of Servlets

• Container-managed web components• Replace Common Gateway Interface(CGI) or

Active Server Pages (ASP)• Generate dynamic response to requests from

web based clients• Synchronize multiple concurrent client request• Serve as client proxies

What is J2EE?

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Servlet Operation

• Server is Java program that runs as separate thread inside servlet container.

• Servlet container is part of web server

• It interact with web client using response request paradigm

What is J2EE?

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JavaServer Pages (JSP)

• Text based documents describe how to process a request and create a response

• Contains HTML or XML and other JSP elements defined by JSP specification.

• Are Installed on web server • are web components that sits on top of

java servlet mode.

What is J2EE?

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JSP Advantages

• Performance– Runtime characteristics of servlets

• uses Lightweight threads: Doesn’t start new process for each request, Initialized once and persists in memory for multiple requests, cached

– Automatic recompilation of modified pages– Server side processing

• Programming– Emphasize use of reusable components– Write Once , Run Anywhere properties– Extensible through custom tag libraries

• Provides front end access mechanism to EJBs

What is J2EE?

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Parts of JSP Pages

Directive<%@ page import=“java.util.”, MVCApp.Cart, MVCApp.CartItem” %>

Declaration<%! Iterator it = null; CartItem ci = null; Vector cpi = null;%>

Raw HTML<html><head><title>Shopping Cart</title></head></html>

Action<jsp:usebean id =“Cart” scope = “session” class = “MVCApp.Cart”/>

Scriplets%Cpi = cart.getCartItems ( );it = cpi.iterator();While (it.hasNext()){ci= (Cart Item)it.next();%>

What is J2EE?

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Parts of JSP Pages

• Expression

<td<% = ci.getTitle() %></td>

<td align =“right”><%=ci.getQuantity()%></td>• Implicit Objects

<% string action = request.getParameter(“action”) ; %>

What is J2EE?

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Enterprise Java Beans (EJBs)

• Entity Beans Represent persistent business Entity Persisted in storage system ( usually Database) Might contain Application logic intrinsic to entity

• Session Beans Perform work for individual clients on the server Encapsulate complex business logic Can coordinate transactional work on multiple entity

beans

What is J2EE?

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States and Persistence

• Session beans can be– Stateless- belong to client for duration of a method

call– Stateful- belong to client for duration of client

conversation

• Entity beans can have– Bean-managed persistence- The developer writes

SQL code to retrieve,store and update database– Container managed persistence- The developer

provide database mapping information that allows the container to manage persistence

What is J2EE?

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Example of EJB Application

• It consists of number of clients accessing session beans and entity beans

• Each Session bean provides specialized processing on behalf of client

e.g. Travel Agent session bean makes travel reservations while Flight Scheduler bean schedules planes to fly on various routes.

• Each Entity Bean represent different type of business entity.

e.g.Passengers, seats, planes, flights are entity beans

What is J2EE?

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Example: Travel AgencyWhat is J2EE?

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How to use J2EE ?

• Using J2EE SDK 1.3.1 to Design, Develop, Assemble and Deploy Applications

How to use J2EE?

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How to run J2EE application on J2EE SDK 1.3.1

• Preparation• Write and compile codes<Start J2EE SDK> to Assemble, Deploy, and Run the application

• Packaging– Creating the J2EE Application (.ear)– Creating the Enterprise Bean (.jar)– Creating the Web Client (.war)

• Deploying• Running

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Preparation

• Install J2EE SDK 1.3.1 on your system• Set Environment Variables

– JAVA_HOME = root directory of J2SE SDK installation

– J2EE_HOME = root directory of J2EE SDK installation

– PATH= %PATH%;%JAVA_HOME%\bin;%J2EE_HOME%\bin

– CLASSPATH= %CLASSPATH%;%J2EE_HOME%\lib\j2ee.jar

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Creating Web Component

When web client such as browser communicates with J2EE application, it dose so through server-side objects called Web components

• Writes and compiles the source code• Bundles the .class, .jsp, .html files into WAR file

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An enterprise bean is a server-side component that contains the business logic of an application

• Write and compile the source code• Package the bean’s classes into EJB JAR file

– Remote Interface– Home Interface– Enterprise Bean Class

Creating Enterprise Bean

RemoteClient

RemoteInterface

HomeInterface

EJB

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Remote Interface

• WebAddressAccount.java– defines the business methods that a client may call.

The business methods are implemented in the enterprise bean code

public interface WebAddressAccount extends EJBObject {

public String getUrlName();

public String getUrlDescript();

}

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Home Interface

• WebAddressAccountHome.java– defines the methods that allow a client to create,

find, or remove an enterprise bean

public interface WebAddressAccountHome extends EJBHome {

public WebAddressAccount create(String urlName, String urlDescript);

public WebAddressAccount findByPrimaryKey(String urlName) ;

}

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Enterprise Bean Class

• WebAddressAccountBean.java– implements the business methods

public class WebAddressAccountBean implements EntityBean {

public String getUrlName() { return urlName;}

public String getUrlDescript() { return urlDescript; }

public String ejbCreate( String urlName, String urlDescript) {

insertRow( urlName, urlDescript);

}

public String ejbFindByPrimaryKey(String primaryKey) {

result = selectByPrimaryKey(primaryKey);

}

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Start J2EE SDK to Assemble, Deploy, and Run the application

• Start Cloudscape database server. – C:\> cloudscape –start

• Start J2EE server – C:\> j2ee –verbose

• Start deploytool– C:\> deploytool

• Build the database table– C:\> cloudscape –isql

WebAddressAccount

urlName (PK)

urlDescription

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Packaging

• Create an Enterprise Archive (EAR) file – ProjectApp.ear

• Add Java Archive (JAR) files and Web Archive (WAR) files to the EAR– WebAddressAccountJAR: contains the enterprise

bean files and related files– ProjectWAR: contains the Web Component files and

related files

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Example: BonusApp

• Objective:

To calculate bonus for an employee

• 3-Tier Example using Session Bean

• 4-Tier Example using Entity Bean

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3 Tier Example: using session bean

1. Create HTML page

2. Create Servlet

3. Create the Session Bean

4. Compile the Session Bean and Servlet

5. Start the J2EE Application Server

6. Start the Deploy tool

7. Assemble the J2EE application

8. Specify JNDI Name and Root Context

9. Verify and Deploy the J2EE application

10. Run the J2EE application

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3 Tier Example: using session bean

• 3-tier– Html page– Servlet– Session Bean

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bonus.html

<HTML><BODY BGCOLOR = "WHITE"><BLOCKQUOTE><H3>Bonus Calculation</H3><FORM METHOD="GET"

ACTION=“bonusServlet"><P>Enter social security Number:<P><INPUT TYPE="TEXT" NAME="SOCSEC"></INPUT><P>Enter Multiplier:<P><INPUT TYPE="TEXT" NAME="MULTIPLIER"></INPUT><P><INPUT TYPE="SUBMIT" VALUE="Submit"><INPUT TYPE="RESET"></FORM></BLOCKQUOTE></BODY></HTML>

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BonusServlet.javapublic class bonusServlet extends HttpServlet {

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Create Session Bean: CalcHome, Calc, CalcBean

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CalcHome.Java

BonusServlet does not work directly with the session bean, but creates an instance of its home interface. The home interface extends EJBHome and has a create method for creating the session bean in its container.

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Calc.java

When the home interface is created, the J2EE application server creates the remote interface and session bean. The remote interface extends EJBObject and declares the calcBonus method for calculating the bonus value. This method is required to throw javax.rmi.RemoteException, and is implemented by the CalcBean class.

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CalcBean.java

The session bean class implements the SessionBean interface and provides behavior for thecalcBonus method. The setSessionContext and ejbCreate methods are called in thatorder by the container after BonusServlet calls the create method in CalcHome.

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Source Codes

CalcHome.javaBonusServlet.javabonus.html

Session BeanServletHTML

Calc.java

CalcBean.java

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Start the Application Server

• Start the Application Server

J2ee –verbose• Start the deploytool

deploytool

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Assemble the J2EE Application

1. Create a new J2EE application (BonusApp.ear).

2. Create a new enterprise bean (CalcBean.jar).

3. Create a new web component (Bonus.war).

4. Specify JNDI name for the enterprise bean (calcs).

5. Specify the Root Context for the J2EE application (BonusRoot).

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2. Create a New EnterpriseBean

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3. Create a new web component (Bonus.war).

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JNDI Names and Resource References

• JNDI: Java Naming and Directory Interface• J2EE components locate objects by invoking the

JNDI lookup method

• The JNDI name of a resource and the name of the resource reference are not the same

• This approach to naming requires that you map the two names before deployment

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Specifying a Resource Reference

The WebAddressAccountBean code refers to the database as follows: private String dbName = "java:comp/env/jdbc/WebAddressAccountDB";

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Mapping Resource Referenceto JNDI Name

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Deploy the application

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Run the application

In the browser, type http://localhost:8000/BonusRoot/bonus.html

• Fill in a social security number• Fill in a multiplier• Click the Submit button. BonusServlet processes your data and returns an HTML page with the bonus calculation on it.

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4 Tier Example: using entity bean/cooperating enterprise beans

• 4-tier– Html– Servlet– EJBs– Database

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Create Entity Bean: Bonus Home (Home interface), Bonus (Remote interface)

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Create Entity Bean: Bonus Home (Home interface), Bonus (Remote interface)

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4 Tier Example: using JavaServer Pages

• 4-tier– Client– JSP– EJBs– Database

JavaServer Pages (JSP) technology lets you put segments of servlet code directly into a static HTML page. When the JSP Page is loaded by a browser, the servlet code executes and the application server creates, compiles, loads, and runs a background servlet to execute the servlet code segments and return an HTML page or print an XML report.

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4 Tier Example: Bonus.jsp

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Modifying the J2EE Application

• Change the source code • Recompile it• Redeploy the application

– Select Tools -> Update Files– Select Tools -> Deploy

Or– Select Tools -> Update And Redeploy

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Advantages & Disadvantages

• Advantages

• Disadvantages– Learning curve– Overhead of a layered architecture: no direct

communication between layers that are apart, affecting performance

– Moving target, i.e. upgraded versions

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Conclusion : Summary

• Need for server-side/enterprise processing with enhanceability, reusability, and scalability

• J2EE as a web-based, component-based multi-tiered client/server architecture

• Designing, developing, assembling, and deploying java applications using a platform

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Conclusion: Research Issues

(Evolving)Vision still to be realized• Non-functional characteristics (enhanceability,

reusability, scalability, security, etc)

• Integration with other technologies such as CGI-programming and CORBA

• Fuller support for design patterns in software lifecycle

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Reference

• http://java.sun.com/j2ee• http://www.utdallas.edu/~chung/SA/2client

.pdf• http://sdmc.krdl.org.sg:8080/~judice/J2EE.

pdf• http://www.sun.com/developers/evangcent

ral/presentations/j2eeoverview.pdf• http://www.sun.com/developers/

evangcentral/presentations/J2EE.pdf

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Design Patterns: Factory Method

• The Factory Method lets a class defer instantiation to subclasses

• The Factory Pattern promotes loose coupling by eliminating the need to bind application-specific classes into the code.

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Design Patterns: Factory Method

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Design Patterns: Factory Method

The equivalent code :The EJB Client code to talk to an EJB

import javax.naming.*;

public class EJBClient { public static void main (String[] argv) {

// get the JNDI naming context Context initialCtx = new InitialContext (); // use the context to lookup the EJB Home interface AccountHome home=(AccountHome)initialCtx.lookup("Account");// use the Home Interface to create a Session bean object Account account = home.create (10001, "Athul", 100000000.25d); // invoke business methods account.credit (200000000.25d); // remove the object account.remove (); }

}

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Design Patterns: FacadeThe JMS class hierarchy can be somewhat daunting at first glance. The relationships between the classes are straight forward, but they require a sequence of code that is often repeated within a JMS application.

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Design Patterns: facade

The JMS Connection and Session Types Depending upon the message-delivery paradigm you choose, your code must work with the correct ConnectionFactory, Connection, and Session classes. Each interface has a subclass for both the publish/subscribe (Topic) and point-to-point (Queue) message models.

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Design Patterns: Facade

Topic and Queue Subclasses

Topic and Queue extend the Destination abstract interface. Subsequently, MessageProducer and MessageConsumer have subclasses for both message models.

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Design Patterns: Facade

• The com.JMSFacade PackageThis is an example of importing and creating the JMS Facade class,

JMSManager: import com.JMSFacade;

import javax.jms.*;

public class myClass {

JMSManager jmsMgr = new JMSManager();

...

}

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Core J2EE Pattern Catalog

http://java.sun.com/blueprints/patterns/index.html