| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You 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. |
| * <p> |
| * The web container cannot place the filter into service if the init method |
| * either: |
| * <ul> |
| * <li>Throws a ServletException</li> |
| * <li>Does not return within a time period defined by the web |
| * container</li> |
| * </ul> |
| * |
| * @param filterConfig The configuration information associated with the |
| * filter instance being initialised |
| * |
| * @throws ServletException if the initialisation fails |
| */ |
| 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. |
| * |
| * @param request The request to process |
| * @param response The response associated with the request |
| * @param chain Provides access to the next filter in the chain for this |
| * filter to pass the request and response to for further |
| * processing |
| * |
| * @throws IOException if an I/O error occurs during this filter's |
| * processing of the request |
| * @throws ServletException if the processing fails for any other reason |
| */ |
| 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(); |
| |
| } |