1. J2EE Web Development.ppt - NTUAcourses.dbnet.ntua.gr/fsr/6075/1. J2EE Web Development-1.pdf ·...

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J2EE Web Development

Agenda

� Application servers

� What is J2EE?� Main component types� Application Scenarios� J2EE APIs and Services

� Examples

1. Application Servers

� In the beginning, there was darkness and cold. Then, …

Centralized, non-distributed

terminals

mainframe

terminals

Application Servers

� In the 90’s, systems should be client-server

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Application Servers

� Today, enterprise applications use the multi-tier model

Application Servers

� “Multi-tier applications” have several independent components

� An application server provides the infrastructure and services to run such applications

Application Servers

� Application server products can be separated into 3 categories:

� J2EE-based solutions

� Non-J2EE solutions (PHP, ColdFusion, Perl, etc.)

� And the Microsoft solution (ASP/COM and now .NET with ASP.NET, VB.NET, C#, etc.)

J2EE Application Servers

� Major J2EE products:� BEA WebLogic

� IBM WebSphere

� Oracle AS

� Jboss (free open source)

� …

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Web Server and Application Server

Web Server(HTTP Server)

App Server 1

App Server 2

Internet Browser

HTTP(S)

2. What is J2EE?

� It is a public specification that embodies several technologies

� J2EE defines a model for developing multi-tier, web based, enterprise applications with distributed components

J2EE Benefits

� High availability

� Scalability

� Integration with existing systems

� Freedom to choose vendors of application servers, tools, components

� Multi-platform

J2EE Benefits

� Flexibility of scenarios and support to several types of clients

� Programming productivity:

� Services allow developer to focus on business

� Component development facilitates maintenance

and reuse

� Enables deploy-time behaviors

� Supports division of labor

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Main technologies

� JavaServer Pages (JSP)

� Servlet

� Enterprise JavaBeans (EJB)

� JSPs, servlets and EJBs are application components

JSP

� Used for web pages with dynamic content

� Processes HTTP requests (non-blocking call-and-return)

� Accepts HTML tags, special JSP tags, and scriptlets of Java code

� Separates static content from presentation logic

� Can be created by web designer using HTML tools

Servlet

� Used for web pages with dynamic content

� Processes HTTP requests (non-blocking call-and-return)

� Written in Java; uses print statements to render HTML

� Loaded into memory once and then called many times

� Provides APIs for session management

EJB

� EJBs are distributed components used to implement business logic (no UI)

� Developer concentrates on business logic

� Availability, scalability, security, interoperability and integrability handled by the J2EE server

� Client of EJBs can be JSPs, servlets, other EJBs and external aplications

� Clients see interfaces

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J2EE Multi-tier Model

J2EE Application Scenarios

� Multi-tier typical application

J2EE Application Scenarios

� Stand-alone client

J2EE Application Scenarios

� Web-centric application

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J2EE Application Scenarios

� Business-to-business

J2EE Services and APIs

� JDBC

� JavaMail

� Java API for XML Parsing (JAXP)

� Web services APIs

Types of EJB

Session Bean

� Stateful session bean:

� Retains conversational state (data) on behalf of an individual client

� If state changed during this invocation, the same state will be available upon the following invocation

� Example: shopping cart

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Session Bean

� Stateless session bean:

� Contains no user-specific data

� Business process that provides a generic service

� Container can pool stateless beans

� Example: shopping catalog

Entity Bean

� Represents business data stored in a database � persistent object

� Underlying data is normally one row of a table

� A primary key uniquely identifies each bean instance

� Allows shared access from multiple clients

� Can live past the duration of client’s session

� Example: shopping order

Entity Bean

� Bean-managed persistence (BMP): bean developer writes JDBC code to access the database; allows better control for the developer

� Container-managed persistence (CMP):container generates all JDBC code to access the database; developer has less code to write, but also less control

3. Examples

� JSP example

� Servlet example

� EJB example

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JSP example

JSP example<%@ page import="hello.Greeting" %>

<jsp:useBean id="mybean" scope="page" class="hello.Greeting"/>

<jsp:setProperty name="mybean" property="*" />

<html><head><title>Hello, User</title></head><body bgcolor="#ffffff" background="background.gif" >

<%@ include file="dukebanner.html" %>

<table border="0" width="700"><tr><td width="150"> &nbsp; </td>

<td width="550"> <h1>My name is Duke. What's yours?</h1></td></tr>

JSP example<tr> <td width="150" &nbsp; </td> <td width="550"><form method="get"><input type="text" name="username" size="25"> <br><input type="submit" value="Submit"><input type="reset" value="Reset"></td> </tr></form> </table><%

if (request.getParameter("username") != null) {%><%@ include file="response.jsp" %><%

}%></body></html>

Servlet examplepublic class HelloWorldServlet extends HttpServlet {

public void service(HttpServletRequest req,

HttpServletResponse res) throws IOException {

res.setContentType("text/html");

PrintWriter out = res.getWriter();

out.println("<html><head><title>Hello

World Servlet</title></head>");

out.println("<body><h1>Hello

World!</h1></body></html>");

}

}

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EJB Example

// Shopping Cart example

// Home interface

public interface CartHome extends EJBHome {

Cart create(String person)

throws RemoteException, CreateException;

Cart create(String person, String id)

throws RemoteException, CreateException;

}

EJB Example

// Remote interface

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;

}

EJB Example// Enterprise bean class

public class CartEJB implements SessionBean {String customerName, customerId;

Vector contents;private SessionContext sc;

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();

}

EJB Examplepublic 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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EJB Examplepublic 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;

}

. . .}

EJB Example// EJB client (stand-alone application)public class CartClient {

public static void main(String[] args) {try {CartHome home = (CartHome)initial.lookup("MyCart");Cart shoppingCart = home.create("Duke DeEarl", "123");shoppingCart.addBook("The Martian Chronicles");shoppingCart.addBook("2001 A Space Odyssey");shoppingCart.remove();

} catch (BookException ex) {System.err.println("Caught a BookException: "

+ ex.getMessage());} catch (Exception ex) {System.err.println("Caught an unexpected exception!");

}}

}

Questions