J2EE Web Development. Agenda. Application servers. What is J2EE? Main component types Application Scenarios J2EE APIs and Services.

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1 J2EE Web Development Agenda Application servers What is J2EE? Main component types Application Scenarios J2EE APIs and Services Examples 1

2 1. Application Servers In the beginning, there was darkness and cold. Then, mainframe terminals terminals Centralized, non-distributed Application Servers In the 90 s, systems should be clientserver 2

3 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 3

4 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 Jboss (free open source) 4

5 Web Server and Application Server Internet Browser App Server 1 Web Server (HTTP Server) HTTP(S) App Server 2 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 5

6 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 6

7 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 7

8 Servlet Used for web pages with dynamic content Processes HTTP requests (non-blocking calland-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 8

9 J2EE Multi-tier Model J2EE Application Scenarios Multi-tier typical application 9

10 J2EE Application Scenarios Stand-alone client J2EE Application Scenarios Web-centric application 10

11 J2EE Application Scenarios Business-to-business J2EE Services and APIs JDBC JavaMail Java API for XML Parsing (JAXP) Web services APIs 11

12 Types of EJB SessionBean Stateful Stateless EJB Taxonomy EnterpriseBean EntityBean BMP CMP MessageDrivenBean 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 12

13 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 13

14 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 14

15 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> 15

16 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>"); 16

17 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; 17

18 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(); 18

19 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!"); 19

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