1. J2EE – Building Component-based Enterprise Web Applications

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

3. Application Servers
In the 90’s, systems should be client-server

4. Application Servers
Today, enterprise applications use the multi-tier model

5. Application Servers
“Multi-tier applications” have several independent components
An application server provides the infrastructure and services to run such applications

6. 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.)

7. 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)

8. Web Server and Application Server
App Server 1
Internet Browser
Web Server (HTTP Server)
HTTP(S)
App Server 2
The Web Server (also called HTTP Server) serves only static content, typically HTML pages.
The Application server serves dynamic content and contains and environment to execute Java components.
Usually there is a plug-in that must be installed in the web server in order to communicate with the AppServer.
Typically, if the web server is IIS, the communication with the app server is via ISAPI, if it is Apache the communication is via NSAPI, and so on.

9. 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

10. J2EE Benefits High availability Scalability
Integration with existing systems
Freedom to choose vendors of application servers, tools, components
Multi-platform

11. 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. Main technologies JavaServer Pages (JSP) Servlet
Enterprise JavaBeans (EJB)
JSPs, servlets and EJBs are application components

13. 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

14. 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
Actually, an HTTP servlet processes HTTP requests.
APIs for maintaining session data throughout a web application and interacting with the user request  overcomes the limitation of the stateless nature of HTTP.

15. 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

16. J2EE Multi-tier Model

17. J2EE Application Scenarios
Multi-tier typical application

18. J2EE Application Scenarios
Stand-alone client

19. J2EE Application Scenarios
Web-centric application

20. J2EE Application Scenarios
Business-to-business

21. 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

22. JMS
Point-to-point
Destination is “queue”

23. JMS
Publish-subscribe
Destination is “topic”

24. J2EE Services and APIs JNDI - Naming and directory services
Applications use JNDI to locate objects, such as environment entries, EJBs, data sources, message queues
JNDI is implementation independent
Underlying implementation varies: LDAP, DNS, DBMS, etc.

25. 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
J2EE servers are not obliged to implement JTS.
The transaction manager must support distributed transaction, what is typically done with XA.

26. J2EE Services and APIs 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

27. 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

28. J2EE Services and APIs JDBC JavaMail Java API for XML Parsing (JAXP)
Web services APIs
JAXP was added to J2EE v1.3
J2EE v1.3 determines that J2EE products must be capable of exporting enterprise beans using the IIOP protocol. This is required to enable interoperability and to make EJB appear as Corba objects.

29. 3. EJB – a closer look

30. 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

31. 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

32. EJB – The Big Picture

33. EJB at runtime
Client can be local or remote

34. EJB at runtime

35. Types of EJB
New!

36. 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
The type of the session bean (stateless or stateful) is declared in the DD.

37. 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
stateless session beans can have non-client specific state, for example, an open database connection.

38. 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

39. 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

40. 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

41. 4. Examples
JSP example
Servlet example
EJB example

42. JSP example

43. 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>

44. 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>

45. 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>"); }

46. 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) }

47. 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() }

48. 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();

49. 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;
throw new CreateException("Invalid id: " + id);
contents = new Vector();

50. 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;
. . .

51. 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!"); }

52. 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

53. Sources & Resources The J2EE Tutorial. Sun Microsystems
IBM WebSphere Application Server manuals
BEA WebLogic Server manuals