CSC 2720 Building Web Applications Frameworks for Building Web Applications

Model-1 Architecture  A web application is made up of many JSP pages  Each JSP page is regarded as the focal point for the entire application.  Each JSP page  Contains code for extracting HTTP request parameters, call the business logic (implemented in JavaBeans, if not directly in the JSP)  Contains the presentation logics  Suitable for small/simple application

Model-2 Architecture  Also called Model-View-Controller (MVC) architecture  Model: The data  View: Representation of the model  Controller: Processes and responds to events (typically user actions) and update the model accordingly  MVC aims at separating data (model) from user interface (view) so that changes to the user interface will not affect data handling, and that the data can be reorganized without changing the user interface.

Model-2 Architecture in Web Application  One servlet serves as controller (Can be more than one servlet serving as controllers)  The controller handles requests, decides what logic to invoke, and decides what JSP page to apply.  Results are placed in beans (or to objects that can be accessed by the JSP pages.)  Request is forwarded to a JSP page to format result  Different JSP pages can be used to handle different types of presentation  Suitable for large or complicated application

MVC Flow of Control Source:

Implementing MVC with RequestDispatcher 1.Define beans to represent the data 2.Use a servlet to handle requests  Servlet reads request parameters, checks for missing and malformed data, etc. 3.Populate the beans  The servlet invokes business logic (application-specific code) or data-access code to obtain the results. Results are placed in the beans that were defined in step 1.

Implementing MVC with RequestDispatcher 4.Store the bean in the request, session, or servlet context  The servlet calls setAttribute on the request, session, or servlet context objects to store a reference to the beans that represent the results of the request. 5.Forward the request to a JSP page  The servlet determines which JSP page is appropriate to the situation and uses the forward method of RequestDispatcher to transfer control to that page.

Implementing MVC with RequestDispatcher 6.Extract the data from the beans.  The JSP page accesses beans with jsp:useBean and a scope matching the location of step 4. The page then uses jsp:getProperty to output the bean properties.  The JSP page does not create or modify the bean; it merely extracts and displays data that the servlet created.

Example of a Controller … public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String operation = request.getParameter("operation"); if (operation == null) operation = "unknown"; String address; if (operation.equals("order")) address = "/Order.jsp"; else if (operation.equals("cancel")) address = "/Cancel.jsp"; else address = "/UnknownOperation.jsp"; RequestDispatcher dispatcher = request.getRequestDispatcher(address); dispatcher.forward(request, response); }

Web Application Framework  A web application framework is a software framework that is designed to support the development of dynamic websites and Web applications.web application framework  Aims  Improve productivity  Promote code reuse  Minimize errors  Reduce cost of maintenance  Typically based on an MVC architecture and include additional libraries.  e.g.: JavaServer Faces (JSF), Struts

References  Wikipedia 