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Model 2
The second design model is simply called Model 2. This is the recommended architecture to base your Java Web applications on. Model 2 is another name for the Model-View-Controller (MVC) design pattern. In Model 2, there are three main components in an application: the model, the view, and the controller. The MVC pattern is further discussed in Chapter 1.
Note
The term Model 2 was first used in the JavaServer Pages Specification version 0.92.
In Model 2, you have one entry point for all pages and usually a servlet acts as the main controller and JSPs for the presentation. Compared to Model 1, Model 2 applications enjoy the following benefits.
- more rapid to build
- easier to test
- easier to maintain
- easier to extend
Now, you see why servlets and JSPs are used together.
Note
One question commonly asked: if there is only one servlet for the whole application and this is the only entry to the application, doesn’t the performance suffer. Does the servlet container spawn many instances of the servlet? The answer is the container only creates one servlet instance, unless you implement the javax.servlet.SingleThreadModel interface (not recommended and has been deprecated in Servlet 2.4) and performance does not suffer. For more detailed discussion, see my book How Tomcat Works.