001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one 003 * or more contributor license agreements. See the NOTICE file 004 * distributed with this work for additional information 005 * regarding copyright ownership. The ASF licenses this file 006 * to you under the Apache License, Version 2.0 (the 007 * "License"); you may not use this file except in compliance 008 * with the License. You may obtain a copy of the License at 009 * 010 * http://www.apache.org/licenses/LICENSE-2.0 011 * 012 * Unless required by applicable law or agreed to in writing, 013 * software distributed under the License is distributed on an 014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 015 * KIND, either express or implied. See the License for the 016 * specific language governing permissions and limitations 017 * under the License. 018 */ 019 020 // 021 // This source code implements specifications defined by the Java 022 // Community Process. In order to remain compliant with the specification 023 // DO NOT add / change / or delete method signatures! 024 // 025 026 package javax.servlet; 027 028 import java.io.IOException; 029 030 /** 031 * 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. 032 * <br><br> 033 * Filters perform filtering in the <code>doFilter</code> method. Every Filter has access to 034 * a FilterConfig object from which it can obtain its initialization parameters, a 035 * reference to the ServletContext which it can use, for example, to load resources 036 * needed for filtering tasks. 037 * <p> 038 * Filters are configured in the deployment descriptor of a web application 039 * <p> 040 * Examples that have been identified for this design are<br> 041 * 1) Authentication Filters <br> 042 * 2) Logging and Auditing Filters <br> 043 * 3) Image conversion Filters <br> 044 * 4) Data compression Filters <br> 045 * 5) Encryption Filters <br> 046 * 6) Tokenizing Filters <br> 047 * 7) Filters that trigger resource access events <br> 048 * 8) XSL/T filters <br> 049 * 9) Mime-type chain Filter <br> 050 * 051 * @since Servlet 2.3 052 * 053 * @version $Rev: 467553 $ $Date: 2006-10-25 06:01:51 +0200 (Mi, 25. Okt 2006) $ 054 */ 055 public interface Filter { 056 /** 057 * Called by the web container to indicate to a filter that it is being placed into 058 * service. The servlet container calls the init method exactly once after instantiating the 059 * filter. The init method must complete successfully before the filter is asked to do any 060 * filtering work. <br><br> 061 * The web container cannot place the filter into service if the init method either<br> 062 * 1.Throws a ServletException <br> 063 * 2.Does not return within a time period defined by the web container 064 */ 065 public void init(FilterConfig filterConfig) throws ServletException; 066 067 068 /** 069 * The <code>doFilter</code> method of the Filter is called by the container 070 * each time a request/response pair is passed through the chain due 071 * to a client request for a resource at the end of the chain. The FilterChain passed in to this 072 * method allows the Filter to pass on the request and response to the next entity in the 073 * chain.<p> 074 * A typical implementation of this method would follow the following pattern:- <br> 075 * 1. Examine the request<br> 076 * 2. Optionally wrap the request object with a custom implementation to 077 * filter content or headers for input filtering <br> 078 * 3. Optionally wrap the response object with a custom implementation to 079 * filter content or headers for output filtering <br> 080 * 4. a) <strong>Either</strong> invoke the next entity in the chain using the FilterChain object (<code>chain.doFilter()</code>), <br> 081 * 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> 082 * 5. Directly set headers on the response after invocation of the next entity in ther filter chain. 083 */ 084 public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException; 085 086 /** 087 * Called by the web container to indicate to a filter that it is being taken out of service. This 088 * method is only called once all threads within the filter's doFilter method have exited or after 089 * a timeout period has passed. After the web container calls this method, it will not call the 090 * doFilter method again on this instance of the filter. <br><br> 091 * 092 * This method gives the filter an opportunity to clean up any resources that are being held (for 093 * example, memory, file handles, threads) and make sure that any persistent state is synchronized 094 * with the filter's current state in memory. 095 */ 096 public void destroy(); 097 } 098