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
+ */
+public interface Filter {
+
+ /**
+ * Called by the web container to indicate to a filter that it is being
+ * placed into service. The servlet container calls the init method exactly
+ * once after instantiating the filter. The init method must complete
+ * successfully before the filter is asked to do any filtering work.
+ *
+ * The web container cannot place the filter into service if the init method
+ * either
+ * 1.Throws a ServletException
+ * 2.Does not return within a time period defined by the web container
+ */
+ public void init(FilterConfig filterConfig) throws 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 invocation of the next
+ * entity in the filter chain.
+ **/
+ public void doFilter(ServletRequest request, ServletResponse response,
+ FilterChain chain) throws IOException, ServletException;
+
+ /**
+ * Called by the web container to indicate to a filter that it is being
+ * taken out of service. This method is only called once all threads within
+ * the filter's doFilter method have exited or after a timeout period has
+ * passed. After the web container calls this method, it will not call the
+ * doFilter method again on this instance of the filter.
+ *
+ *
+ * This method gives the filter an opportunity to clean up any resources
+ * that are being held (for example, memory, file handles, threads) and make
+ * sure that any persistent state is synchronized with the filter's current
+ * state in memory.
+ */
+ public void destroy();
+
+}