public interface Filter
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 
| Modifier and Type | Method and Description | 
|---|---|
| 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. | 
void init(FilterConfig filterConfig) throws ServletException
The web container cannot place the filter into service if the init method either:
filterConfig - The configuration information associated with the
                     filter instance being initialisedServletException - if the initialisation failsvoid doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws 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.
request - The request to processresponse - The response associated with the requestchain - Provides access to the next filter in the chain for this
                 filter to pass the request and response to for further
                 processingIOException - if an I/O error occurs during this filter's
                     processing of the requestServletException - if the processing fails for any other reasonvoid destroy()
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