CometFilter


1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    * 
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   * 
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  
19  package org.apache.catalina;
20  
21  import java.io.IOException  ;
22  
23  import javax.servlet.Filter  ;
24  import javax.servlet.ServletException  ;
25  
26  /**
27   * A Comet filter, similar to regular filters, performs filtering tasks on either 
28   * the request to a resource (a Comet servlet), or on the response from a resource, or both.
29   * <br><br>
30   * Filters perform filtering in the <code>doFilterEvent</code> method. Every Filter has access to 
31   * a FilterConfig object from which it can obtain its initialization parameters, a
32   * reference to the ServletContext which it can use, for example, to load resources
33   * needed for filtering tasks.
34   * <p>
35   * Filters are configured in the deployment descriptor of a web application
36   * <p>
37   * Examples that have been identified for this design are<br>
38   * 1) Authentication Filters <br>
39   * 2) Logging and Auditing Filters <br>
40   * 3) Image conversion Filters <br>
41   * 4) Data compression Filters <br>
42   * 5) Encryption Filters <br>
43   * 6) Tokenizing Filters <br>
44   * 7) Filters that trigger resource access events <br>
45   * 8) XSL/T filters <br>
46   * 9) Mime-type chain Filter <br>
47   * <br>
48   * 
49   * @author Remy Maucherat
50   * @author Filip Hanik
51   */
52  public interface CometFilter extends Filter   {
53  
54      
55      /**
56       * The <code>doFilterEvent</code> method of the CometFilter is called by the container
57       * each time a request/response pair is passed through the chain due
58       * to a client event for a resource at the end of the chain. The CometFilterChain passed in to this
59       * method allows the Filter to pass on the event to the next entity in the
60       * chain.<p>
61       * A typical implementation of this method would follow the following pattern:- <br>
62       * 1. Examine the request<br>
63       * 2. Optionally wrap the request object contained in the event with a custom implementation to
64       * filter content or headers for input filtering and pass a CometEvent instance containing
65       * the wrapped request to the next filter<br>
66       * 3. Optionally wrap the response object contained in the event with a custom implementation to
67       * filter content or headers for output filtering and pass a CometEvent instance containing
68       * the wrapped request to the next filter<br>
69       * 4. a) <strong>Either</strong> invoke the next entity in the chain using the CometFilterChain object (<code>chain.doFilterEvent()</code>), <br>   
70       * 4. b) <strong>or</strong> not pass on the request/response pair to the next entity in the filter chain to block the event processing<br>
71       * 5. Directly set fields on the response after invocation of the next entity in the filter chain.
72       * 
73       * @param event the event that is being processed. Another event may be passed along the chain.
74       * @param chain 
75       * @throws IOException
76       * @throws ServletException
77       */
78      public void doFilterEvent(CometEvent event, CometFilterChain chain)
79          throws IOException  , ServletException  ;
80      
81  
82  }
83
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