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1   
2   
3   /*
4    * The contents of this file are subject to the terms
5    * of the Common Development and Distribution License
6    * (the "License").  You may not use this file except
7    * in compliance with the License.
8    *
9    * You can obtain a copy of the license at
10   * glassfish/bootstrap/legal/CDDLv1.0.txt or
11   * https://glassfish.dev.java.net/public/CDDLv1.0.html.
12   * See the License for the specific language governing
13   * permissions and limitations under the License.
14   *
15   * When distributing Covered Code, include this CDDL
16   * HEADER in each file and include the License file at
17   * glassfish/bootstrap/legal/CDDLv1.0.txt.  If applicable,
18   * add the following below this CDDL HEADER, with the
19   * fields enclosed by brackets "[]" replaced with your
20   * own identifying information: Portions Copyright [yyyy]
21   * [name of copyright owner]
22   *
23   * Copyright 2005 Sun Microsystems, Inc. All rights reserved.
24   *
25   * Portions Copyright Apache Software Foundation.
26   */
27  
28  package javax.servlet;
29  
30  import java.io.IOException;
31  
32  	/** 
33  	* 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.
34          * <br><br>
35  	* Filters perform filtering in the <code>doFilter</code> method. Every Filter has access to 
36  	** a FilterConfig object from which it can obtain its initialization parameters, a
37  	** reference to the ServletContext which it can use, for example, to load resources
38  	** needed for filtering tasks.
39  	** <p>
40  	** Filters are configured in the deployment descriptor of a web application
41  	** <p>
42  	** Examples that have been identified for this design are<br>
43  	** 1) Authentication Filters <br>
44  	** 2) Logging and Auditing Filters <br>
45  	** 3) Image conversion Filters <br>
46      	** 4) Data compression Filters <br>
47  	** 5) Encryption Filters <br>
48  	** 6) Tokenizing Filters <br>
49  	** 7) Filters that trigger resource access events <br>
50  	** 8) XSL/T filters <br>
51  	** 9) Mime-type chain Filter <br>
52  	 * @since	Servlet 2.3
53  	*/
54  
55  public interface Filter {
56  
57  	/** 
58  	* Called by the web container to indicate to a filter that it is being placed into
59  	* service. The servlet container calls the init method exactly once after instantiating the
60  	* filter. The init method must complete successfully before the filter is asked to do any
61  	* filtering work. <br><br>
62  
63       	* The web container cannot place the filter into service if the init method either<br>
64          * 1.Throws a ServletException <br>
65          * 2.Does not return within a time period defined by the web container 
66  	*/
67  	public void init(FilterConfig filterConfig) throws ServletException;
68  	
69  	
70  	/**
71  	* The <code>doFilter</code> method of the Filter is called by the container
72  	* each time a request/response pair is passed through the chain due
73  	* to a client request for a resource at the end of the chain. The FilterChain passed in to this
74  	* method allows the Filter to pass on the request and response to the next entity in the
75  	* chain.<p>
76  	* A typical implementation of this method would follow the following pattern:- <br>
77  	* 1. Examine the request<br>
78  	* 2. Optionally wrap the request object with a custom implementation to
79  	* filter content or headers for input filtering <br>
80  	* 3. Optionally wrap the response object with a custom implementation to
81  	* filter content or headers for output filtering <br>
82  	* 4. a) <strong>Either</strong> invoke the next entity in the chain using the FilterChain object (<code>chain.doFilter()</code>), <br>   
83  	** 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>
84  	** 5. Directly set headers on the response after invocation of the next entity in the filter chain.
85  	**/
86      public void doFilter ( ServletRequest request, ServletResponse response, FilterChain chain ) throws IOException, ServletException;
87  
88  	/**
89  	* Called by the web container to indicate to a filter that it is being taken out of service. This 
90  	* method is only called once all threads within the filter's doFilter method have exited or after
91  	* a timeout period has passed. After the web container calls this method, it will not call the
92  	* doFilter method again on this instance of the filter. <br><br>
93  	* 
94       	* This method gives the filter an opportunity to clean up any resources that are being held (for
95  	* example, memory, file handles, threads) and make sure that any persistent state is synchronized
96  	* with the filter's current state in memory.
97  	*/
98  
99  	public void destroy();
100 
101 
102 }
103