Filter Big Picture

The middle-tier component of the Java EE architecture consists of an application server often fronted by a web server. These servers serve up web content and execute servlets and JSP pages in response to incoming client requests. Figure 10-1 illustrates how client request flow through a stand-alone application server such as Tomcat.

Filters can be used to do the following:

1. Inspect the request header and data before it reaches the resouce
2. Inspect the response header and data after it has been sent by the resource
3. Provide a Modified version of the request to the resource being processed by the container.
4. Access and modify the response from the resource before returning it .
5. Stop a request from reaching a resource altogether.

Filter life cycle is like servlet. Filter definition and filter mapping.

Matching URL patterns:

/*　　Everything that is served by this web application, including static pages, servlets, and jsp pages.

/servlet/*　　All Servlets under the /servlet path

/jsp/*.jsp

/dept/accounting/*

Filter chain:

javax.servlet.Filter

javax.servlet.FilterChain

All filters are chainable.