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 package javax.servlet; 021 022 import java.io.IOException; 023 024 /** 025 * 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. 026 * <br><br> 027 * Filters perform filtering in the <code>doFilter</code> method. Every Filter has access to 028 ** a FilterConfig object from which it can obtain its initialization parameters, a 029 ** reference to the ServletContext which it can use, for example, to load resources 030 ** needed for filtering tasks. 031 ** <p> 032 ** Filters are configured in the deployment descriptor of a web application 033 ** <p> 034 ** Examples that have been identified for this design are<br> 035 ** 1) Authentication Filters <br> 036 ** 2) Logging and Auditing Filters <br> 037 ** 3) Image conversion Filters <br> 038 ** 4) Data compression Filters <br> 039 ** 5) Encryption Filters <br> 040 ** 6) Tokenizing Filters <br> 041 ** 7) Filters that trigger resource access events <br> 042 ** 8) XSL/T filters <br> 043 ** 9) Mime-type chain Filter <br> 044 * @since Servlet 2.3 045 */ 046 047 public interface Filter { 048 049 /** 050 * Called by the web container to indicate to a filter that it is being placed into 051 * service. The servlet container calls the init method exactly once after instantiating the 052 * filter. The init method must complete successfully before the filter is asked to do any 053 * filtering work. <br><br> 054 055 * The web container cannot place the filter into service if the init method either<br> 056 * 1.Throws a ServletException <br> 057 * 2.Does not return within a time period defined by the web container 058 */ 059 public void init(FilterConfig filterConfig) throws ServletException; 060 061 062 /** 063 * The <code>doFilter</code> method of the Filter is called by the container 064 * each time a request/response pair is passed through the chain due 065 * to a client request for a resource at the end of the chain. The FilterChain passed in to this 066 * method allows the Filter to pass on the request and response to the next entity in the 067 * chain.<p> 068 * A typical implementation of this method would follow the following pattern:- <br> 069 * 1. Examine the request<br> 070 * 2. Optionally wrap the request object with a custom implementation to 071 * filter content or headers for input filtering <br> 072 * 3. Optionally wrap the response object with a custom implementation to 073 * filter content or headers for output filtering <br> 074 * 4. a) <strong>Either</strong> invoke the next entity in the chain using the FilterChain object (<code>chain.doFilter()</code>), <br> 075 ** 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> 076 ** 5. Directly set headers on the response after invocation of the next entity in the filter chain. 077 **/ 078 public void doFilter ( ServletRequest request, ServletResponse response, FilterChain chain ) throws IOException, ServletException; 079 080 /** 081 * Called by the web container to indicate to a filter that it is being taken out of service. This 082 * method is only called once all threads within the filter's doFilter method have exited or after 083 * a timeout period has passed. After the web container calls this method, it will not call the 084 * doFilter method again on this instance of the filter. <br><br> 085 * 086 * This method gives the filter an opportunity to clean up any resources that are being held (for 087 * example, memory, file handles, threads) and make sure that any persistent state is synchronized 088 * with the filter's current state in memory. 089 */ 090 091 public void destroy(); 092 093 094 } 095