1 copyright 2002 © paulo merson j2ee – building component-based enterprise web applications...

Copyright 2002 © Paulo Merson 1

J2EE – Building J2EE – Building Component-based EnterpriseComponent-based Enterprise

Web ApplicationsWeb Applications

05/09/200205/09/2002

Paulo Merson


Agenda1. Application servers2. What is J2EE?

Main component types Application Scenarios J2EE APIs and Services

3. EJB – a closer look4. 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


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 Sun iPlanet Application Server Oracle 9iAS HP/Bluestone Total-e-Server Borland AppServer Jboss (free open source)


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

Current version is 1.3 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


J2EE Benefits

Don’t forget to say

that Java is cool!


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


J2EE Multi-tier Model


J2EE Application Scenarios

Multi-tier typical application



Stand-alone client



Web-centric application



Business-to-business


J2EE Services and APIs

Java Message Service (JMS) Implicit invocation Communication is loosely coupled,

reliable and asynchronous Supports 2 models:

point-to-point publish/subscribe


JMS Point-to-point

Destination is “queue”


JMS Publish-subscribe

Destination is “topic”



JNDI - Naming and directory services Applications use JNDI to locate objects,

such as environment entries, EJBs, datasources, message queues

JNDI is implementation independent Underlying implementation varies: LDAP,

DNS, DBMS, etc.



Transaction service: Controls transactions automatically You can demarcate transactions explicitly Or you can specify relationships between

methods that make up a single transaction



Security Java Authentication and Authorization Service

(JAAS) is the new (J2EE 1.3) standard for J2EE security

Authentication via userid/password or digital certificates

Role-based authorization limits access of users to resources (URLs, EJB methods)

Embedded security realm



J2EE Connector Architecture Integration to non-J2EE systems, such as

mainframes and ERPs. Standard API to access different EIS Vendors implement EIS-specific resource

adapters Support to Corba clients



JDBC JavaMail Java API for XML Parsing (JAXP) Web services APIs


3. EJB – a closer look


Home Interface

Methods to create, remove or locate EJB objects

The home interface implementation is the home object (generated)

The home object is a factory


Remote Interface

Business methods available to clients The remote interface implementation

is the EJB object (generated) The EJB object acts as a proxy to the

EJB instance


EJB – The Big Picture


EJB at runtime

Client can be local or remote


EJB at runtime


Types of EJB

EJB Taxonomy

Sta te ful

Sta te le ss

SessionBea n

BMP

C MP

EntityBea n M essa geDrivenBea n

Ente rp riseBea n

New!


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


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


Message-Driven Bean

Message consumer for a JMS queue or topic

Benefits from EJB container services that are not available to standard JMS consumers

Has no home or remote interface Example: order processing – stock info


4. Examples

JSP example Servlet example EJB example


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


JSP example<tr> <td width="150" </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>");

}

}


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 classpublic 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 Example public 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(); }


EJB Example public 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


Sources & Resources Java 2 Platform Enterprise Edition

Specification, v1.3 Designing Enterprise Applications with the

Java 2, Enterprise Edition. Nicholas Kassen and the Enterprise Team

Does the App Server Maket Still Exist? Jean-Christophe Cimetiere

The State of The J2EE Application Server Market. Floyd Marinescu


Sources & Resources

The J2EE Tutorial. Sun Microsystems IBM WebSphere Application Server

manuals BEA WebLogic Server manuals www.java.sun.com/j2ee www.theserverside.com

1 copyright 2002 © paulo merson j2ee – building component-based enterprise web applications...

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