1. JSP Application Models

2. Review • A JavaBean is a reusable software component that is manipulated in a builder tool. • get() and set() methods are used with the property for which the data has to be set. • The features of JavaBeans are methods, events, properties, introspection and serialization. • JavaBeans have four scopes; page, request, session and application. • JAR is a compressed file containing the Java classes. • Every JavaBean is a Java class, but every Java class may not be a JavaBean. • <jsp:useBean> tag is used for creating reference in any code. • The Bean tag provides the page a means to encapsulate business logic separately from the content presentation. • The key components of JavaMail APIs are session, message and transport.

3. JSP Application Models Overview • Consists of Java code, HTML codes, and JSP tags • Two approaches for building JSP applications are: • Model 1 • Model 2

4. Model 1 Architecture • Represents a page-centric design • Developed using scripting elements, custom tags, and a scripting language • Client request is directly processed by JSP page • JSP page accesses the database through JavaBeans to generate a response • Model 1 applications are difficult to modify

5. Model 2 Architecture • Represents a controller design • Suitable for large and complex applications • Consists of a combination of servlets, JSP and JavaBeans • Based on Model-View-Controller (MVC) pattern

6. Model 2 Architecture (cont.) • The MVC pattern includes: • Model – Represents the application object or data that serves multiple views • View – Represents the presentation component or the user interface component of the data model • Controller – Responds to the input in the user interface. The controller transmits the request, and selects a view for presenting data to the user.

7. Implementing Model 2 Architecture • Requires controller servlet, request handler, page beans and JSP views • Controller servlet handles the incoming request, and forwards to the request handler for further processing • The handleRequest()method of the RequestHandler interface processes the request, and returns the URL of the JSP view

8. J2EE Framework • Provides enterprise services, such as transactions and security • Uses enterprise beans as a component • Enables low and high level data communication, design pattern, and a component model that enables to build reusable components

9. J2EE Framework - Components • Servlet – Consists of get() and post() methods, that are used for requesting data in dynamic Web applications • Session bean – Consist of temporary objects that enable to distribute and isolate the processing task. The two forms of shared data are: • Stateful • Stateless • Entity bean – Represents the data items, such as rows in a result set. The two forms of entity beans are: • Container managed persistence • Bean managed persistence

10. J2EE Framework – Components (cont.) • Java terminologies – Includes terminologies, such as Java Naming and Directory Interface (JNDI), Enterprise JavaBeans (EJB), servlets, JavaServer Pages (JSP), Extensible Markup Language (XML) and Remote Method Invocation (RMI) that are used in Web applications • Java Virtual Machine (JVM) – Provides a consistent execution platform for running Java codes

11. J2EE Framework - Benefits • Common application model – Enables to create distributed, reliable, scalable and secure Web applications • Generic infrastructure - Provides compatibility across vendors by introducing a standard Application Program Interface (API) • Easy deployment and execution - Simplifies the task of deploying and running the Web application

12. RequestDispatcher Interface • Forwards the request from a JSP page or a servlet to other resources • Other resources process the request and send a response to the client • The RequestDispatcher interface encapsulates the URL of a resource • Two methods of RequestDispatcher interface are: • Include() • Forward()

13. RequestDispatcher Interface Methods

14. Using Methods - Code Snippets Includes page from specified URL <jsp:include page="localURL" flush="true "> <jsp:param name="parameterName1" value="parameterValue1"/> //code <jsp:param name="parameterName1" value="parameterValue1"/> </jsp:include> Additional request parameters Using Include () Transfers control to specified URL <jsp:forward page="localURL "> <jsp:param name="parameterName1" value="parameterValue1"/> //code <jsp:param name="parameterNameN" value="parameterValueN "/> </jsp:forward> Additional request parameters Using Forward ()

15. Exception Handling • Exceptions are errors that can occur in a JSP page • The JSP page traps and handles request time errors • Unhandled exceptions are forwarded to the error page • Syntax <%@ page errorPage=“errorpage.jsp” %> • Set the isErrorPage attribute of page directive to true, to make a JSP page an error handler • Syntax <%@ page isErrorPage=“true” %>

16. Exception Handling - Cont… • Translation time - Occurs when the JSP source file is converted to servlets class file. The JSP engine handles translation time errors. • Request time - Occurs during the processing of the request. Request time errors are the runtime errors that throw exceptions. <html> <body> <%@ page isErrorPage="true" %> Detected Error: <br> <%= exception.getMessage() %> </body> </html> Makes JSP page an error handler Returns error message Code Snippet to create an error page

17. Exception Handling - Cont… Forwards the unhandled exception to errorpage.jsp <%@ page errorPage="errorpage.jsp" %> <% if (request.getParameter("param ").equals("value ")) { // code } //The test above will throw a NullPointerException if param is // not part of the query string. A better implementation is: if ("value".equals(request.getParameter("param "))) { // code } %> Code Snippet to transfer control to the error page

18. Summary • JSP technology enables the user to separate the presentation logic with the programming logic • The user can make JSP page easy to read and maintain, by embedding HTML or XML in the JSP page • Model 1 application is developed using scripting elements, custom tags, and a scripting language, such as JavaScript • JSP page directly processes the request, and sends response to the client in Model 1 architecture • The Model 2 applications are based on Model-View-Controller (MVC) pattern: • Model • View • Controller

19. Summary – Cont… • J2EE framework provides ready to use enterprise services, such as transactions and security • The RequestDispatcher interface forwards the request from a JSP page or a servlet to other resources, such as HTML file, servlet, or a JSP page • The two methods in RequesDispatcher interface are: • include() • forward() • The unhandled exceptions are forwarded to the error handler file • The errors in JSP page includes: • Translation time • Request time

20. Q & A