Learn Java for Web Development

66 CHAPTER 2: Building Web Applications Using Servlets and JSP

 Providing actions on web components by using a chain of filters in a specific order  Modifying the response headers and response data before they are rendered

A filter is created by implementing the javax.servlet.Filter interface and providing a no-arg
constructor. A filter is configured in a web application either in the deployment descriptor using
the element or in the @WebFilterannotation (introduced in the section that follows). In the

element, you must declare the following:

   <filter-name>: Used to map the filter to a servlet or URL

   <filter-class>: Used by the container to identify the filter type

Note You can also declare the initialization parameters for a filter.

Listing 2-9 illustrates the filter declaration.

Listing 2-9. Declaring the Filter

ResponseFilter

com.apress.ResponseServlet

Filters can be associated with a servlet using the element. Listing 2-10 maps the
Response Filter filter to the ResponseServlet servlet.

Listing 2-10. Mapping the Filter to the Servlet

Response Filter

ResponseServlet

Filters can be associated with groups of servlets using , as illustrated in Listing 2-11.

Listing 2-11. Associating a Filter with a Group of Servlets

Response Filter

/*

In Listing 2-11 the response filter is applied to all the servlets in the web application.

A web application typically comprises the following filtering components:

   Authentication filters

   Caching filters

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