J2EE : Why, What and How TM University of Texas at Dallas Anna Yi.

Download Report

Transcript J2EE : Why, What and How TM University of Texas at Dallas Anna Yi.

J2EE TM

: Why, What and How

University of Texas at Dallas Anna Yi 1

Objectives

• Why J2EE?

• What is J2EE?

• How to use J2EE?

Why J2EE?

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 3

Why J2EE?

Two-tier Client/Server Architecture

Server Client 4

Why J2EE?

Simple Web Client/Server • Interaction of two-tier architecture • Client: simply accesses web pages through web browser • Server: retrieves html documents 5

Why J2EE?

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 6

Why J2EE?

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 7

Why J2EE?

Two-tier Client/Server Architecture

• 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 Client Server But what is the problem with this architecture?

Why J2EE?

Drawbacks of two tier application architecture • Easy to deploy, but difficult to enhance or upgrade • Reusability of business and presentation logic difficult • Not scalable 9

Why J2EE?

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 10

Why J2EE?

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) 11

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 12

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 13

What is J2EE?

Thin-client Multi-tiered Architecture 14

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 15

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 16

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), extensible (can add functionality) more 17

What is J2EE?

The Big Picture

What is J2EE?

4-Tier Model

Client Tier Web Tier EIS Tier Business Tier 20

What is J2EE?

Commercial Platforms

• J2EE SDK 1.3 (Sun) * • WebLogic (BEA Systems) • WebSphere (IBM) • iPlanet (Sun & NetScape) • JBoss (Open source) 21

What is J2EE?

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 22

Application Server: Key Services 23

JBoss- Application Server

What is J2EE?

J2EE Components

• Java Servlets • JavaServer Pages (JSP) • Enterprise JavaBeans (EJB) 25

What is J2EE?

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 31

What is J2EE?

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 32

What is J2EE?

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?

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 34

What is J2EE?

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

Shopping Cart

Action

Scriplets

% Cpi = cart.getCartItems ( ); it = cpi.iterator(); While (it.hasNext()){ci= (Cart Item)it.next(); %> 35

What is J2EE?

Parts of JSP Pages

• Expression <%=ci.getQuantity()%> • Implicit Objects <% string action = request.getParameter(“action”) ; %> 36

What is J2EE?

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 37

What is J2EE?

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 38

What is J2EE?

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 39

What is J2EE?

Example: Travel Agency

How to use J2EE?

How to use J2EE ?

• Using J2EE SDK 1.3.1 to Design, Develop, Assemble and Deploy Applications 41

How to run J2EE application on J2EE SDK 1.3.1

• Preparation • Write and compile codes 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 42

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

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 44

Creating Enterprise Bean

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 Remote Client – Enterprise Bean Class Remote Interface Home Interface EJB 45

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(); 48

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) ; 49

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); 50

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 t WebAddressAccoun urlName (PK) urlDescription 51

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 53

Example: BonusApp

• Objective: To calculate bonus for an employee • 3-Tier Example using Session Bean • 4-Tier Example using Entity Bean 54

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 55

3 Tier Example: using session bean • 3-tier – Html page – Servlet – Session Bean 56

bonus.html

Bonus Calculation

Enter social security Number:

Enter Multiplier:

BonusServlet.java

public class bonusServlet extends HttpServlet { 59

Create Session Bean: CalcHome, Calc, CalcBean 60

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.

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.

CalcBean.java

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

Source Codes

HTML

bonus.html

Servlet

BonusServlet.java

Session Bean

CalcHome.java

Calc.java

CalcBean.java

Start the Application Server

• Start the Application Server

J2ee –verbose

• Start the deploytool

deploytool

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).

2. Create a New EnterpriseBean 67

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

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 69

Specifying a Resource Reference The WebAddressAccountBean code refers to the database as follows: private String dbName = "java:comp/env/jdbc/WebAddressAccountDB"; 70

Mapping Resource Reference to JNDI Name 71

Deploy the application

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.

4 Tier Example: using entity bean/ cooperating enterprise beans • 4-tier – Html – Servlet – EJBs – Database 74

Create Entity Bean:

Bonus Home (Home interface), Bonus (Remote interface) 75

Create Entity Bean:

Bonus Home (Home interface), Bonus (Remote interface) 76

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.

4 Tier Example: Bonus.jsp

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 80

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 81

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 82

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 83

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/evangcent ral/presentations/J2EE.pdf

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. 85

Design Patterns: Factory Method 86

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

(); } }

Design Patterns: Facade

The 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. 88

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. 89

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. 90

Design Patterns: Facade

•

The com.JMSFacade Package

This 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(); ... } 91

Core J2EE Pattern Catalog

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