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A filter is an object that performs 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 
| Method Summary | |
|  void | destroy()Called by the web container to indicate to a filter that it is being taken out of service. | 
|  void | doFilter(ServletRequest request,
         ServletResponse response,
         FilterChain chain)The doFiltermethod 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. | 
|  void | init(FilterConfig filterConfig)Called by the web container to indicate to a filter that it is being placed into service. | 
| Method Detail | 
public void init(FilterConfig filterConfig)
          throws ServletException
ServletException
public void doFilter(ServletRequest request,
                     ServletResponse response,
                     FilterChain chain)
              throws java.io.IOException,
                     ServletException
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 invocation of the next entity in the filter chain.
java.io.IOException
ServletExceptionpublic void destroy()
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