MVC

This week applies MVC to the design and implementation of the Electronic Voting System of Labs 3 and 4. This includes writing servlets to control and dispatch, beans and POJOs to model the data and the business rules, and JSP pages to author the view.

• The controller must control and dispatch by relying on the Model and forwarding to a JSP
• Tomcat provides three Map<String,Object> data structures to hold data with three levels of persistence: context, session, and request. A fourth level (available only to JSP servlets is the page).
• State can be captured using the session object. Its API allows us to detect the start of new sessions.
• The model is best packaged as a Java package.
• The model uses beans and POJOs. It is compiled (using javac) and tested outside Tomcat.
• The servlet's init method is responsible for instantiating the model and storing it in the application scope.
• Jasper translates a JSP page to a servlet upon receiving the first reference to it (typically from a servlet forward).
• Jasper allows us to embed three things in the JSP page: template code (such as HTML) which is served as-is, Expression Language [EL] which is served after evaluation, and special action tags which are served after executing the code behind them. It also support a few directives such as content type.
• EL uses a number of built-in implicit objects.
• Actions are either standard (JSTL) or custom.

• Complete Labs 3 by doing Lab-4.
• Read Chapter 6 up to and excluding Section 6.7.
• Read Chapter 8 up to and excluding Section 8.5.
• Look at the basic implementation of EVS in the Resource Directory under evs.
• Look at ELdemo.jspx and JSTLdemo.jspx in the Resource Directory under jsp.