J2ee

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Paulo Merson
Copyright 2002 © Paulo Merson 1

Agenda
1. Application servers
2. What is J2EE?
 Main component types
 Application Scenarios
 J2EE APIs and Services
1. EJB – a closer look
2. Examples

1. Application Servers
 In the beginning, there was darkness and
cold. Then, …
mainframe
Centralized, non-distributed
terminals
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

E n te rp ris e B e a n
E n tity B e a n M e s s a g e D riv e n B e a n
Types of EJB
E J B T a x o n o m y
S e s s io n B e a n
S ta te fu l
S ta te le s s
B M P
C M P
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 example
public 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 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 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

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