J2EE – Building Component-based Enterprise Web Applications

J2EE – Building Component-based Enterprise Web Applications
05/09/2002 Paulo Merson Copyright 2002 © Paulo Merson

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

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

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. Copyright 2002 © Paulo Merson

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

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

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

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 Copyright 2002 © Paulo Merson

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. Copyright 2002 © Paulo Merson

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 Copyright 2002 © Paulo Merson

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

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

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

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. Copyright 2002 © Paulo Merson

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 Copyright 2002 © Paulo Merson

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

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. Copyright 2002 © Paulo Merson

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

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. Copyright 2002 © Paulo Merson

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. Copyright 2002 © Paulo Merson

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

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

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

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> Copyright 2002 © Paulo Merson

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> Copyright 2002 © Paulo Merson

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>"); } Other servlet examples implement the doPost() and/or doGet() methods. These methods reply only to POST or GET requests; if you want to handle all request types from a single method, your servlet can simply implement the service() method. (However, if you choose to implement the service() method, you will not be able to implement the doPost() or doGet() methods, unless you call super.service() at the beginning of the service() method.) Copyright 2002 © Paulo Merson

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) } Many details are omitted in the source code examples. Copyright 2002 © Paulo Merson

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() } Copyright 2002 © Paulo Merson

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(); Copyright 2002 © Paulo Merson

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(); Copyright 2002 © Paulo Merson

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; . . . Copyright 2002 © Paulo Merson

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!"); } Copyright 2002 © Paulo Merson

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

J2EE – Building Component-based Enterprise Web Applications

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