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J2EE TM : Why, What and How

J2EE TM : Why, What and How. University of Texas at Dallas Anna Yi. Objectives. Why J2EE? What is J2EE? How to use J2EE?. Motivation for J2EE. Why J2EE?. Need for New multi-tier enterprise computing model in web environment A way to bring in different elements of enterprise application

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J2EE TM : Why, What and How

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  1. J2EETM : Why, What and How University of Texas at Dallas Anna Yi

  2. Objectives • Why J2EE? • What is J2EE? • How to use J2EE?

  3. Motivation for J2EE Why J2EE? • Need for • New multi-tier enterprise computing model in web environment • A way to bring in different elements of enterprise application • Web interface design • Transaction processing • Meeting non-functional system requirements: • Availability, reliability, enhanceability, performance, scalability, reusability, interoperability • Timely development and deployment

  4. Two-tier Client/Server Architecture Why J2EE? Server Client

  5. Simple Web Client/Server Why J2EE? • Interaction of two-tier architecture • Client: simply accesses web pages through web browser • Server: retrieves html documents

  6. CGI-based Web Client/Server Why J2EE? • Interaction of two-tier architecture • Client: uses service requiring 2ndary storage • Server: manipulates forms, Database updates, (primitive) electronic commerce • Fat Server/ Thin Client

  7. Java Applet-based Web Client/Server Why J2EE? • Interaction of two-tier architecture • Client: uses Java Applet for client-side computation • Server: provides Applet bytecode • Fat Client/Thin Server

  8. Server Client Why J2EE? Two-tier Client/Server Architecture But what is the problem with this architecture? • So, important processing needs to be run on the server • Then, Java needs to run on the server too to be more useful  enterprise • The server is almost like what CGI-programming does • Client: data access applying business logic and presentation of data (computation) • Server: serves only as service-database server, not application server web server

  9. Drawbacks of two tier application architecture Why J2EE? • Easy to deploy, but difficult to enhance or upgrade • Reusability of business and presentation logic difficult • Not scalable

  10. Vision of J2EE Why J2EE? • An open standard • Umbrella for anything Java-related • For designing, developing, assembling, and deploying component-based enterprise applications • Separation of business logic from presentation • Reusability, enhanceability, scalability, interoperability

  11. Separation of Business logic from Presentation logic Why J2EE? • Presentation logic : display • Business logic : what the company wants to do Example: the distribution of different sales figures by diff dept (business logic) can be represented in many different ways (pie chart, bar graph, etc)

  12. Why J2EE? • Simplifies the complexity of a building n-tier application • Standardizes an API between components and application server container • J2EE Application Server and Containers provide the framework services

  13. What is J2EE? • Defines the standard for developing multitier enterprise applications • Simplifies enterprise applications by: • Basing them on standardized, modular components • Providing a complete set of services to those components • Handling many details of application behavior automatically, without complex programming

  14. Thin-client Multi-tiered Architecture What is J2EE?

  15. J2EE Tiers • Client Presentation • HTML or Java applets deployed in Browser • XML documentations transmitted through HTTP • Java clients running in Client Java Virtual Machine (JVM) • Presentation Logic • Servlets or JavaServer Pages running in web server • Application Logic • Enterprise JavaBeans running in Server

  16. J2EE Components & Services • Components • Java Servlets • JavaServer Pages (JSP) • Enterprise JavaBeans (EJB) • Standard services & supporting technologies • Java database connectivity(JDBC) data access API • Java Messaging Service (JMS) (Remote Method Invocations (RMI)) • Extensible Markup Languages(XML) • JavaIDL (Interface Description Language) • JavaMail • Java Security • CORBA technology • Design Patterns

  17. Advantages of Multi-tiers • Tiers separate functionality: • Presentation Logic, Business Logic, Data Schema • Easier upgrade since one tier can be changed without changing the rest • Lower deployment and maintenance cost • More flexible (can support changes), more extensible (can add functionality)

  18. The Big Picture What is J2EE?

  19. 4-Tier Model What is J2EE? Web Tier Client Tier EIS Tier Business Tier

  20. Commercial Platforms What is J2EE? • J2EE SDK 1.3 (Sun) * • WebLogic (BEA Systems) • WebSphere (IBM) • iPlanet (Sun & NetScape) • JBoss (Open source)

  21. What is J2EE? What is Application Server • Application servers enable the development of multi-tiered distributed applications. They are also called “middleware” • An application server acts as the interface between the database(s), the web servers and the client browsers

  22. Application Server: Key Services

  23. JBoss- Application Server

  24. What is J2EE? J2EE Components • Java Servlets • JavaServer Pages (JSP) • Enterprise JavaBeans (EJB)

  25. What is J2EE? Overview of Servlets • Container-managed web components • Replace Common Gateway Interface(CGI) or Active Server Pages (ASP) • Generate dynamic response to requests from web based clients • Synchronize multiple concurrent client request • Serve as client proxies

  26. What is J2EE? Servlet Operation • Server is Java program that runs as separate thread inside servlet container. • Servlet container is part of web server • It interact with web client using response request paradigm

  27. What is J2EE? JavaServer Pages (JSP) • Text based documents describe how to process a request and create a response • Contains HTML or XML and other JSP elements defined by JSP specification. • Are Installed on web server • are web components that sits on top of java servlet mode.

  28. What is J2EE? JSP Advantages • Performance • Runtime characteristics of servlets • uses Lightweight threads: Doesn’t start new process for each request, Initialized once and persists in memory for multiple requests, cached • Automatic recompilation of modified pages • Server side processing • Programming • Emphasize use of reusable components • Write Once , Run Anywhere properties • Extensible through custom tag libraries • Provides front end access mechanism to EJBs

  29. What is J2EE? Parts of JSP Pages Directive <%@ page import=“java.util.”, MVCApp.Cart, MVCApp.CartItem” %> Declaration <%! Iterator it = null; CartItem ci = null; Vector cpi = null;%> Raw HTML <html><head><title>Shopping Cart</title></head></html> Action <jsp:usebean id =“Cart” scope = “session” class = “MVCApp.Cart”/> Scriplets % Cpi = cart.getCartItems ( ); it = cpi.iterator(); While (it.hasNext()){ci= (Cart Item)it.next(); %>

  30. What is J2EE? Parts of JSP Pages • Expression <td<% = ci.getTitle() %></td> <td align =“right”><%=ci.getQuantity()%></td> • Implicit Objects <% string action = request.getParameter(“action”) ; %>

  31. What is J2EE? Enterprise Java Beans (EJBs) • Entity Beans • Represent persistent business Entity • Persisted in storage system ( usually Database) • Might contain Application logic intrinsic to entity • Session Beans • Perform work for individual clients on the server • Encapsulate complex business logic • Can coordinate transactional work on multiple entity beans

  32. What is J2EE? States and Persistence • Session beans can be • Stateless- belong to client for duration of a method call • Stateful- belong to client for duration of client conversation • Entity beans can have • Bean-managed persistence- The developer writes SQL code to retrieve,store and update database • Container managed persistence- The developer provide database mapping information that allows the container to manage persistence

  33. What is J2EE? Example of EJB Application • It consists of number of clients accessing session beans and entity beans • Each Session bean provides specialized processing on behalf of client e.g. Travel Agent session bean makes travel reservations while Flight Scheduler bean schedules planes to fly on various routes. • Each Entity Bean represent different type of business entity. e.g.Passengers, seats, planes, flights are entity beans

  34. What is J2EE? Example: Travel Agency

  35. How to use J2EE? How to use J2EE ? • Using J2EE SDK 1.3.1 to Design, Develop, Assemble and Deploy Applications

  36. How to run J2EE application on J2EE SDK 1.3.1 • Preparation • Write and compile codes <Start J2EE SDK> to Assemble, Deploy, and Run the application • Packaging • Creating the J2EE Application (.ear) • Creating the Enterprise Bean (.jar) • Creating the Web Client (.war) • Deploying • Running

  37. Preparation • Install J2EE SDK 1.3.1 on your system • Set Environment Variables • JAVA_HOME = root directory of J2SE SDK installation • J2EE_HOME = root directory of J2EE SDK installation • PATH = %PATH%;%JAVA_HOME%\bin;%J2EE_HOME%\bin • CLASSPATH = %CLASSPATH%;%J2EE_HOME%\lib\j2ee.jar

  38. Creating Web Component When web client such as browser communicates with J2EE application, it dose so through server-side objects called Web components • Writes and compiles the source code • Bundles the .class, .jsp, .html files into WAR file

  39. Remote Interface Remote Client EJB Home Interface Creating Enterprise Bean An enterprise bean is a server-side component that contains the business logic of an application • Write and compile the source code • Package the bean’s classes into EJB JAR file • Remote Interface • Home Interface • Enterprise Bean Class

  40. Remote Interface • WebAddressAccount.java • defines the business methods that a client may call. The business methods are implemented in the enterprise bean code public interface WebAddressAccount extends EJBObject { public String getUrlName(); public String getUrlDescript(); }

  41. Home Interface • WebAddressAccountHome.java • defines the methods that allow a client to create, find, or remove an enterprise bean public interface WebAddressAccountHome extends EJBHome { public WebAddressAccount create(String urlName, String urlDescript); public WebAddressAccount findByPrimaryKey(String urlName) ; }

  42. Enterprise Bean Class • WebAddressAccountBean.java • implements the business methods public class WebAddressAccountBean implements EntityBean { public String getUrlName() { return urlName; } public String getUrlDescript() { return urlDescript; } public String ejbCreate( String urlName, String urlDescript) { insertRow( urlName, urlDescript); } public String ejbFindByPrimaryKey(String primaryKey) { result = selectByPrimaryKey(primaryKey); }

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