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1   /*
2    *  Licensed to the Apache Software Foundation (ASF) under one
3    *  or more contributor license agreements.  See the NOTICE file
4    *  distributed with this work for additional information
5    *  regarding copyright ownership.  The ASF licenses this file
6    *  to you under the Apache License, Version 2.0 (the
7    *  "License"); you may not use this file except in compliance
8    *  with the License.  You may obtain a copy of the License at
9    *
10   *    http://www.apache.org/licenses/LICENSE-2.0
11   *
12   *  Unless required by applicable law or agreed to in writing,
13   *  software distributed under the License is distributed on an
14   *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15   *  KIND, either express or implied.  See the License for the
16   *  specific language governing permissions and limitations
17   *  under the License.
18   *
19   */
20  package org.apache.mina.core.filterchain;
21  
22  import org.apache.mina.core.service.IoHandler;
23  import org.apache.mina.core.session.IdleStatus;
24  import org.apache.mina.core.session.IoSession;
25  import org.apache.mina.core.write.WriteRequest;
26  import org.apache.mina.filter.util.ReferenceCountingFilter;
27  
28  /**
29   * A filter which intercepts {@link IoHandler} events like Servlet
30   * filters.  Filters can be used for these purposes:
31   * <ul>
32   *   <li>Event logging,</li>
33   *   <li>Performance measurement,</li>
34   *   <li>Authorization,</li>
35   *   <li>Overload control,</li>
36   *   <li>Message transformation (e.g. encryption and decryption, ...),</li>
37   *   <li>and many more.</li>
38   * </ul>
39   * <p>
40   * <strong>Please NEVER implement your filters to wrap
41   * {@link IoSession}s.</strong> Users can cache the reference to the
42   * session, which might malfunction if any filters are added or removed later.
43   *
44   * <h3>The Life Cycle</h3>
45   * {@link IoFilter}s are activated only when they are inside {@link IoFilterChain}.
46   * <p>
47   * When you add an {@link IoFilter} to an {@link IoFilterChain}:
48   * <ol>
49   *   <li>{@link #init()} is invoked by {@link ReferenceCountingFilter} if
50   *       the filter is added at the first time.</li>
51   *   <li>{@link #onPreAdd(IoFilterChain, String, NextFilter)} is invoked to notify
52   *       that the filter will be added to the chain.</li>
53   *   <li>The filter is added to the chain, and all events and I/O requests
54   *       pass through the filter from now.</li>
55   *   <li>{@link #onPostAdd(IoFilterChain, String, NextFilter)} is invoked to notify
56   *       that the filter is added to the chain.</li>
57   *   <li>The filter is removed from the chain if {@link #onPostAdd(IoFilterChain, String, org.apache.mina.core.filterchain.IoFilter.NextFilter)}
58   *       threw an exception.  {@link #destroy()} is also invoked by
59   *       {@link ReferenceCountingFilter} if the filter is the last filter which
60   *       was added to {@link IoFilterChain}s.</li>
61   * </ol>
62   * <p>
63   * When you remove an {@link IoFilter} from an {@link IoFilterChain}:
64   * <ol>
65   *   <li>{@link #onPreRemove(IoFilterChain, String, NextFilter)} is invoked to
66   *       notify that the filter will be removed from the chain.</li>
67   *   <li>The filter is removed from the chain, and any events and I/O requests
68   *       don't pass through the filter from now.</li>
69   *   <li>{@link #onPostRemove(IoFilterChain, String, NextFilter)} is invoked to
70   *       notify that the filter is removed from the chain.</li>
71   *   <li>{@link #destroy()} is invoked by {@link ReferenceCountingFilter} if
72   *       the removed filter was the last one.</li>
73   * </ol>
74   *
75   * @author <a href="http://mina.apache.org">Apache MINA Project</a>
76   *
77   * @see IoFilterAdapter
78   */
79  public interface IoFilter {
80      /**
81       * Invoked by {@link ReferenceCountingFilter} when this filter
82       * is added to a {@link IoFilterChain} at the first time, so you can
83       * initialize shared resources.  Please note that this method is never
84       * called if you don't wrap a filter with {@link ReferenceCountingFilter}.
85       */
86      void init() throws Exception;
87  
88      /**
89       * Invoked by {@link ReferenceCountingFilter} when this filter
90       * is not used by any {@link IoFilterChain} anymore, so you can destroy
91       * shared resources.  Please note that this method is never called if
92       * you don't wrap a filter with {@link ReferenceCountingFilter}.
93       */
94      void destroy() throws Exception;
95  
96      /**
97       * Invoked before this filter is added to the specified <tt>parent</tt>.
98       * Please note that this method can be invoked more than once if
99       * this filter is added to more than one parents.  This method is not
100      * invoked before {@link #init()} is invoked.
101      *
102      * @param parent the parent who called this method
103      * @param name the name assigned to this filter
104      * @param nextFilter the {@link NextFilter} for this filter.  You can reuse
105      *                   this object until this filter is removed from the chain.
106      */
107     void onPreAdd(IoFilterChain parent, String name, NextFilter nextFilter)
108             throws Exception;
109 
110     /**
111      * Invoked after this filter is added to the specified <tt>parent</tt>.
112      * Please note that this method can be invoked more than once if
113      * this filter is added to more than one parents.  This method is not
114      * invoked before {@link #init()} is invoked.
115      *
116      * @param parent the parent who called this method
117      * @param name the name assigned to this filter
118      * @param nextFilter the {@link NextFilter} for this filter.  You can reuse
119      *                   this object until this filter is removed from the chain.
120      */
121     void onPostAdd(IoFilterChain parent, String name, NextFilter nextFilter)
122             throws Exception;
123 
124     /**
125      * Invoked before this filter is removed from the specified <tt>parent</tt>.
126      * Please note that this method can be invoked more than once if
127      * this filter is removed from more than one parents.
128      * This method is always invoked before {@link #destroy()} is invoked.
129      *
130      * @param parent the parent who called this method
131      * @param name the name assigned to this filter
132      * @param nextFilter the {@link NextFilter} for this filter.  You can reuse
133      *                   this object until this filter is removed from the chain.
134      */
135     void onPreRemove(IoFilterChain parent, String name, NextFilter nextFilter)
136             throws Exception;
137 
138     /**
139      * Invoked after this filter is removed from the specified <tt>parent</tt>.
140      * Please note that this method can be invoked more than once if
141      * this filter is removed from more than one parents.
142      * This method is always invoked before {@link #destroy()} is invoked.
143      *
144      * @param parent the parent who called this method
145      * @param name the name assigned to this filter
146      * @param nextFilter the {@link NextFilter} for this filter.  You can reuse
147      *                   this object until this filter is removed from the chain.
148      */
149     void onPostRemove(IoFilterChain parent, String name, NextFilter nextFilter)
150             throws Exception;
151 
152     /**
153      * Filters {@link IoHandler#sessionCreated(IoSession)} event.
154      */
155     void sessionCreated(NextFilter nextFilter, IoSession session)
156             throws Exception;
157 
158     /**
159      * Filters {@link IoHandler#sessionOpened(IoSession)} event.
160      */
161     void sessionOpened(NextFilter nextFilter, IoSession session)
162             throws Exception;
163 
164     /**
165      * Filters {@link IoHandler#sessionClosed(IoSession)} event.
166      */
167     void sessionClosed(NextFilter nextFilter, IoSession session)
168             throws Exception;
169 
170     /**
171      * Filters {@link IoHandler#sessionIdle(IoSession,IdleStatus)}
172      * event.
173      */
174     void sessionIdle(NextFilter nextFilter, IoSession session, IdleStatus status)
175             throws Exception;
176 
177     /**
178      * Filters {@link IoHandler#exceptionCaught(IoSession,Throwable)}
179      * event.
180      */
181     void exceptionCaught(NextFilter nextFilter, IoSession session,
182             Throwable cause) throws Exception;
183 
184     /**
185      * Filters {@link IoHandler#messageReceived(IoSession,Object)}
186      * event.
187      */
188     void messageReceived(NextFilter nextFilter, IoSession session,
189             Object message) throws Exception;
190 
191     /**
192      * Filters {@link IoHandler#messageSent(IoSession,Object)}
193      * event.
194      */
195     void messageSent(NextFilter nextFilter, IoSession session,
196             WriteRequest writeRequest) throws Exception;
197 
198     /**
199      * Filters {@link IoSession#close()} method invocation.
200      */
201     void filterClose(NextFilter nextFilter, IoSession session) throws Exception;
202 
203     /**
204      * Filters {@link IoSession#write(Object)} method invocation.
205      */
206     void filterWrite(NextFilter nextFilter, IoSession session,
207             WriteRequest writeRequest) throws Exception;
208     
209     /**
210      * Represents the next {@link IoFilter} in {@link IoFilterChain}.
211      */
212     public interface NextFilter {
213         /**
214          * Forwards <tt>sessionCreated</tt> event to next filter.
215          */
216         void sessionCreated(IoSession session);
217 
218         /**
219          * Forwards <tt>sessionOpened</tt> event to next filter.
220          */
221         void sessionOpened(IoSession session);
222 
223         /**
224          * Forwards <tt>sessionClosed</tt> event to next filter.
225          */
226         void sessionClosed(IoSession session);
227 
228         /**
229          * Forwards <tt>sessionIdle</tt> event to next filter.
230          */
231         void sessionIdle(IoSession session, IdleStatus status);
232 
233         /**
234          * Forwards <tt>exceptionCaught</tt> event to next filter.
235          */
236         void exceptionCaught(IoSession session, Throwable cause);
237 
238         /**
239          * Forwards <tt>messageReceived</tt> event to next filter.
240          */
241         void messageReceived(IoSession session, Object message);
242 
243         /**
244          * Forwards <tt>messageSent</tt> event to next filter.
245          */
246         void messageSent(IoSession session, WriteRequest writeRequest);
247 
248         /**
249          * Forwards <tt>filterWrite</tt> event to next filter.
250          */
251         void filterWrite(IoSession session, WriteRequest writeRequest);
252 
253         /**
254          * Forwards <tt>filterClose</tt> event to next filter.
255          */
256         void filterClose(IoSession session);
257         
258     }
259 }