javax.servlet
Interface Filter


public interface Filter

A filter is an object than perform filtering tasks on either the request to a resource (a servlet or static content), or on the response from a resource, or both.

Filters perform filtering in the doFilter method. Every Filter has access to a FilterConfig object from which it can obtain its initialization parameters, a reference to the ServletContext which it can use, for example, to load resources needed for filtering tasks.

Filters are configured in the deployment descriptor of a web application

Examples that have been identified for this design are
1) Authentication Filters
2) Logging and Auditing Filters
3) Image conversion Filters
4) Data compression Filters
5) Encryption Filters
6) Tokenizing Filters
7) Filters that trigger resource access events
8) XSL/T filters
9) Mime-type chain Filter

Since:
Servlet 2.3

Method Summary
 void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
          The doFilter method of the Filter is called by the container each time a request/response pair is passed through the chain due to a client request for a resource at the end of the chain.
 FilterConfig getFilterConfig()
          Return the FilterConfig for this Filter.
 void setFilterConfig(FilterConfig filterConfig)
          The container calls this method when the Filter is instantiated and passes in a FilterConfig object.
 

Method Detail

setFilterConfig

public void setFilterConfig(FilterConfig filterConfig)
The container calls this method when the Filter is instantiated and passes in a FilterConfig object. When the container is done with the Filter, it calls this method, passing in null.

getFilterConfig

public FilterConfig getFilterConfig()
Return the FilterConfig for this Filter.

doFilter

public void doFilter(ServletRequest request,
                     ServletResponse response,
                     FilterChain chain)
              throws java.io.IOException,
                     ServletException
The doFilter method of the Filter is called by the container each time a request/response pair is passed through the chain due to a client request for a resource at the end of the chain. The FilterChain passed in to this method allows the Filter to pass on the request and response to the next entity in the chain.

A typical implementation of this method would follow the following pattern:-
1. Examine the request
2. Optionally wrap the request object with a custom implementation to filter content or headers for input filtering
3. Optionally wrap the response object with a custom implementation to filter content or headers for output filtering
4. a) Either invoke the next entity in the chain using the FilterChain object (chain.doFilter()),
4. b) or not pass on the request/response pair to the next entity in the filter chain to block the request processing
5. Directly set headers on the response after invokation of the next entity in ther filter chain.



Copyright (c) 1999-2000 The Apache Software Foundation. All Rights Reserved.