J2EE Web Development 13/1/ Application Servers. Application Servers. Agenda. In the beginning, there was darkness and cold.

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1 1. Application Servers J2EE Web Development In the beginning, there was darkness and cold. Then, mainframe terminals terminals Centralized, non-distributed Agenda Application servers What is J2EE? Main component types Application Scenarios J2EE APIs and Services Application Servers In the 90 s, systems should be clientserver Examples 1

2 Application Servers Today, enterprise applications use the multi-tier model 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.) Application Servers Multi-tier applications have several independent components An application server provides the infrastructure and services to run such applications J2EE Application Servers Major J2EE products: BEA WebLogic IBM WebSphere Oracle AS Jboss (free open source) 2

3 Web Server and Application Server Internet Browser HTTP(S) Web Server (HTTP Server) App Server 1 App Server 2 J2EE Benefits High availability Scalability Integration with existing systems Freedom to choose vendors of application servers, tools, components Multi-platform 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 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 3

4 Main technologies JavaServer Pages (JSP) Servlet Enterprise JavaBeans (EJB) JSPs, servlets and EJBs are application components 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 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 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 4

5 J2EE Multi-tier Model J2EE Application Scenarios Stand-alone client J2EE Application Scenarios Multi-tier typical application J2EE Application Scenarios Web-centric application 5

6 J2EE Application Scenarios Types of EJB Business-to-business J2EE Services and APIs JDBC JavaMail Java API for XML Parsing (JAXP) Web services APIs 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 6

7 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 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 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 3. Examples JSP example Servlet example EJB example 7

8 JSP example 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> 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> 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>"); 8

9 // 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; // 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(); // 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; 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(); 9

10 public void addbook(string title) { contents. addelement(title); Questions 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 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!"); 10