| /* |
| * Copyright 2004 The Apache Software Foundation |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package javax.servlet; |
| |
| import java.io.IOException; |
| |
| /** |
| * 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. |
| * <br><br> |
| * Filters perform filtering in the <code>doFilter</code> 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. |
| ** <p> |
| ** Filters are configured in the deployment descriptor of a web application |
| ** <p> |
| ** Examples that have been identified for this design are<br> |
| ** 1) Authentication Filters <br> |
| ** 2) Logging and Auditing Filters <br> |
| ** 3) Image conversion Filters <br> |
| ** 4) Data compression Filters <br> |
| ** 5) Encryption Filters <br> |
| ** 6) Tokenizing Filters <br> |
| ** 7) Filters that trigger resource access events <br> |
| ** 8) XSL/T filters <br> |
| ** 9) Mime-type chain Filter <br> |
| * @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. <br><br> |
| |
| * The web container cannot place the filter into service if the init method either<br> |
| * 1.Throws a ServletException <br> |
| * 2.Does not return within a time period defined by the web container |
| */ |
| public void init(FilterConfig filterConfig) throws ServletException; |
| |
| |
| /** |
| * The <code>doFilter</code> 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.<p> |
| * A typical implementation of this method would follow the following pattern:- <br> |
| * 1. Examine the request<br> |
| * 2. Optionally wrap the request object with a custom implementation to |
| * filter content or headers for input filtering <br> |
| * 3. Optionally wrap the response object with a custom implementation to |
| * filter content or headers for output filtering <br> |
| * 4. a) <strong>Either</strong> invoke the next entity in the chain using the FilterChain object (<code>chain.doFilter()</code>), <br> |
| ** 4. b) <strong>or</strong> not pass on the request/response pair to the next entity in the filter chain to block the request processing<br> |
| ** 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. <br><br> |
| * |
| * 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(); |
| |
| |
| } |
| |