The document provides an overview of Java 2 Platform, Enterprise Edition (J2EE) and its application servers, emphasizing their role in developing multi-tier, web-based enterprise applications. It covers the main components of J2EE, including JavaServer Pages (JSP), servlets, and Enterprise JavaBeans (EJB), detailing their functionalities and benefits. Additionally, it addresses the types of application servers and key APIs and services, such as Java Message Service (JMS), security, and transaction management.

1. JJ22EEEE –– BBuuiillddiinngg
CCoommppoonneenntt--bbaasseedd EEnntteerrpprriissee
WWeebb AApppplliiccaattiioonnss
0055//0099//22000022
Paulo Merson
Copyright 2002 © Paulo Merson 1

2. Copyright 2002 © Paulo Merson 2
Agenda
1. Application servers
2. What is J2EE?
 Main component types
 Application Scenarios
 J2EE APIs and Services
1. EJB – a closer look
2. Examples

3. 1. Application Servers
 In the beginning, there was darkness and
cold. Then, …
mainframe
Centralized, non-distributed
terminals
Copyright 2002 © Paulo Merson 3
terminals

4. Application Servers
 In the 90’s, systems should be client-server
Copyright 2002 © Paulo Merson 4

5. Application Servers
Today, enterprise applications use
the multi-tier model
Copyright 2002 © Paulo Merson 5

6. Application Servers
 “Multi-tier applications” have several
independent components
 An application server provides the
infrastructure and services to run such
applications
Copyright 2002 © Paulo Merson 6

7. 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.)
Copyright 2002 © Paulo Merson 7

8. 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)
Copyright 2002 © Paulo Merson 8

9. Web Server and Application Server
Web Server
(HTTP Server)
App Server 1
App Server 2
Copyright 2002 © Paulo Merson 9
Internet Browser
HTTP(S)

10. 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
Copyright 2002 © Paulo Merson 10

11. J2EE Benefits
 High availability
 Scalability
 Integration with existing systems
 Freedom to choose vendors of
application servers, tools, components
 Multi-platform
Copyright 2002 © Paulo Merson 11

12. 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
Copyright 2002 © Paulo Merson 12

13. J2EE Benefits
Don’t forget to say
that Java is cool!
Copyright 2002 © Paulo Merson 13

14. Main technologies
 JavaServer Pages (JSP)
 Servlet
 Enterprise JavaBeans (EJB)
 JSPs, servlets and EJBs are application
components
Copyright 2002 © Paulo Merson 14

15. Copyright 2002 © Paulo Merson 15
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

16. Copyright 2002 © Paulo Merson 16
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

17. Copyright 2002 © Paulo Merson 17
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

18. J2EE Multi-tier Model
Copyright 2002 © Paulo Merson 18

19. J2EE Application Scenarios
 Multi-tier typical application
Copyright 2002 © Paulo Merson 19

20. J2EE Application Scenarios
 Stand-alone client
Copyright 2002 © Paulo Merson 20

21. J2EE Application Scenarios
 Web-centric application
Copyright 2002 © Paulo Merson 21

22. J2EE Application Scenarios
 Business-to-business
Copyright 2002 © Paulo Merson 22

23. 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
Copyright 2002 © Paulo Merson 23

24. Copyright 2002 © Paulo Merson 24
JMS
 Point-to-point
 Destination is “queue”

25. Copyright 2002 © Paulo Merson 25
JMS
 Publish-subscribe
 Destination is “topic”

26. J2EE Services and APIs
 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.
Copyright 2002 © Paulo Merson 26

27. J2EE Services and APIs
 Transaction service:
 Controls transactions automatically
 You can demarcate transactions explicitly
 Or you can specify relationships between
methods that make up a single transaction
Copyright 2002 © Paulo Merson 27

28. J2EE Services and APIs
Copyright 2002 © Paulo Merson 28
 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

29. J2EE Services and APIs
 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
Copyright 2002 © Paulo Merson 29

30. J2EE Services and APIs
 JDBC
 JavaMail
 Java API for XML Parsing (JAXP)
 Web services APIs
Copyright 2002 © Paulo Merson 30

31. 3. EJB – a closer look
Copyright 2002 © Paulo Merson 31

32. 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
Copyright 2002 © Paulo Merson 32

33. 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
Copyright 2002 © Paulo Merson 33

34. Copyright 2002 © Paulo Merson 34

35. EJB – The Big Picture
Copyright 2002 © Paulo Merson 35

36. EJB at runtime
Client can be local or remote
Copyright 2002 © Paulo Merson 36

37. EJB at runtime
Copyright 2002 © Paulo Merson 37

38. 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
Copyright 2002 © Paulo Merson 38
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!

39. Copyright 2002 © Paulo Merson 39
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

40. Copyright 2002 © Paulo Merson 40
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

41. 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
Copyright 2002 © Paulo Merson 41

42. 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
Copyright 2002 © Paulo Merson 42

43. 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
Copyright 2002 © Paulo Merson 43

44. Copyright 2002 © Paulo Merson 44
4. Examples
 JSP example
 Servlet example
 EJB example

45. Copyright 2002 © Paulo Merson 45
JSP example

46. Copyright 2002 © Paulo Merson 46
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>

47. Copyright 2002 © Paulo Merson 47
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>

48. 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>");
Copyright 2002 © Paulo Merson 48
}
}

49. Copyright 2002 © Paulo Merson 49
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;
}

50. Copyright 2002 © Paulo Merson 50
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;
}

51. Copyright 2002 © Paulo Merson 51
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();
}

52. Copyright 2002 © Paulo Merson 52
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();
}

53. Copyright 2002 © Paulo Merson 53
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;
}
. . .
}

54. Copyright 2002 © Paulo Merson 54
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!");
}
}
}

55. Copyright 2002 © Paulo Merson 55
Questions

56. 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
Copyright 2002 © Paulo Merson 56

57. Sources & Resources
 The J2EE Tutorial. Sun Microsystems
 IBM WebSphere Application Server
manuals
 BEA WebLogic Server manuals
 www.java.sun.com/j2ee
 www.theserverside.com
Copyright 2002 © Paulo Merson 57