SE452: Configuring Web Apps (more web.xml) [22/24]

The servlet and a servlet-mapping element are important sections in the deployment descriptor (web.xml).

servlet element: the servlet definition

• It defines a name for a servlet by mapping the name to the class name of the servlet.
• It sets initialization parameters.
• Different servlet names can be mapped to the same servlet class.

servlet-mapping element: servlet mapping

• It maps a URL or a URL pattern to a servlet name.
• Different URL can be mapped to the same servlet name.

An example webapp for a simple servlet:

        
<web-app>
  <servlet>
   <servlet-name>hello</servlet-name>
   <servlet-class>HelloServlet</servlet-class>
  </servlet>
  <servlet-mapping>
   <servlet-name>hello</servlet-name>
   <url-pattern>/hello</url-pattern>
  </servlet-mapping>
</web-app>

    
        

A servlet can be invoked with the URL specified in the servlet mapping:

• http://localhost:8080/myapps/hello
• http://localhost:8080/se452/hello

http://localhost:8080 protocol, host, and port

/se452,/myapps the context prefix

/hello the servlet url

Sometimes we want to initialize a servlet when it is first loaded by the servlet engine.

• configuration
• specialization
• customization

Initialization parameters are usually handled in the init() method.

        void init()
        

Override this one to initialize a servlet

        void init( ServletConfig config)
        

Do not override this one, if you do override, you must call super.init(ServletConfig config) You can access the ServletConfig's methods through the servlet itself, since the interface is implemented by GenericServlet