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Java > Open Source Codes > org > apache > mina > filter > CompressionFilter


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.filter;
21
22 import java.io.IOException JavaDoc;
23
24 import org.apache.mina.common.ByteBuffer;
25 import org.apache.mina.common.IoFilter;
26 import org.apache.mina.common.IoFilterAdapter;
27 import org.apache.mina.common.IoFilterChain;
28 import org.apache.mina.common.IoSession;
29 import org.apache.mina.filter.support.Zlib;
30
31 /**
32  * An {@link IoFilter} which compresses all data using
33  * <a HREF="http://www.jcraft.com/jzlib/">JZlib</a>.
34  * Support for the LZW (DLCZ) algorithm is also planned.
35  * <p>
36  * This filter only supports compression using the <tt>PARTIAL FLUSH</tt> method,
37  * since that is the only method useful when doing stream level compression.
38  * <p>
39  * This filter supports compression/decompression of the input and output
40  * channels selectively. It can also be enabled/disabled on the fly.
41  * <p>
42  * This filter does not discard the zlib objects, keeping them around for the
43  * entire life of the filter. This is because the zlib dictionary needs to
44  * be built up over time, which is used during compression and decompression.
45  * Over time, as repetitive data is sent over the wire, the compression efficiency
46  * steadily increases.
47  * <p>
48  * Note that the zlib header is written only once. It is not necessary that
49  * the data received after processing by this filter may not be complete due
50  * to packet fragmentation.
51  * <p>
52  * It goes without saying that the other end of this stream should also have a
53  * compatible compressor/decompressor using the same algorithm.
54  *
55  * @author The Apache Directory Project (mina-dev@directory.apache.org)
56  * @version $Rev: 555855 $, $Date: 2007-07-13 12:19:00 +0900 (금, 13 7월 2007) $
57  */
58 public class CompressionFilter extends IoFilterAdapter {
59     /**
60      * Max compression level. Will give the highest compression ratio, but
61      * will also take more cpu time and is the slowest.
62      */
63     public static final int COMPRESSION_MAX = Zlib.COMPRESSION_MAX;
64
65     /**
66      * Provides the best speed at the price of a low compression ratio.
67      */
68     public static final int COMPRESSION_MIN = Zlib.COMPRESSION_MIN;
69
70     /**
71      * No compression done on the data.
72      */
73     public static final int COMPRESSION_NONE = Zlib.COMPRESSION_NONE;
74
75     /**
76      * The default compression level used. Provides the best balance
77      * between speed and compression
78      */
79     public static final int COMPRESSION_DEFAULT = Zlib.COMPRESSION_DEFAULT;
80
81     /**
82      * A session attribute that stores the {@link Zlib} object used for compression.
83      */
84     private static final String JavaDoc DEFLATER = CompressionFilter.class.getName()
85             + ".Deflater";
86
87     /**
88      * A session attribute that stores the {@link Zlib} object used for decompression.
89      */
90     private static final String JavaDoc INFLATER = CompressionFilter.class.getName()
91             + ".Inflater";
92
93     /**
94      * A flag that allows you to disable compression once.
95      */
96     public static final String JavaDoc DISABLE_COMPRESSION_ONCE = CompressionFilter.class
97             .getName()
98             + ".DisableCompressionOnce";
99
100     private boolean compressInbound = true;
101
102     private boolean compressOutbound = true;
103
104     private int compressionLevel;
105
106     /**
107      * Creates a new instance which compresses outboud data and decompresses
108      * inbound data with default compression level.
109      */
110     public CompressionFilter() {
111         this(true, true, COMPRESSION_DEFAULT);
112     }
113
114     /**
115      * Creates a new instance which compresses outboud data and decompresses
116      * inbound data with the specified <tt>compressionLevel</tt>.
117      *
118      * @param compressionLevel the level of compression to be used. Must
119      * be one of {@link #COMPRESSION_DEFAULT},
120      * {@link #COMPRESSION_MAX},
121      * {@link #COMPRESSION_MIN}, and
122      * {@link #COMPRESSION_NONE}.
123      */
124     public CompressionFilter(final int compressionLevel) {
125         this(true, true, compressionLevel);
126     }
127
128     /**
129      * Creates a new instance.
130      *
131      * @param compressInbound <tt>true</tt> if data read is to be decompressed
132      * @param compressOutbound <tt>true</tt> if data written is to be compressed
133      * @param compressionLevel the level of compression to be used. Must
134      * be one of {@link #COMPRESSION_DEFAULT},
135      * {@link #COMPRESSION_MAX},
136      * {@link #COMPRESSION_MIN}, and
137      * {@link #COMPRESSION_NONE}.
138      */
139     public CompressionFilter(final boolean compressInbound,
140             final boolean compressOutbound, final int compressionLevel) {
141         this.compressionLevel = compressionLevel;
142         this.compressInbound = compressInbound;
143         this.compressOutbound = compressOutbound;
144     }
145
146     public void messageReceived(NextFilter nextFilter, IoSession session,
147             Object JavaDoc message) throws Exception JavaDoc {
148         if (!compressInbound) {
149             nextFilter.messageReceived(session, message);
150             return;
151         }
152
153         Zlib inflater = (Zlib) session.getAttribute(INFLATER);
154         if (inflater == null) {
155             throw new IllegalStateException JavaDoc();
156         }
157
158         ByteBuffer inBuffer = (ByteBuffer) message;
159         ByteBuffer outBuffer = inflater.inflate(inBuffer);
160         inBuffer.release();
161         nextFilter.messageReceived(session, outBuffer);
162     }
163
164     /*
165      * @see org.apache.mina.common.IoFilter#filterWrite(org.apache.mina.common.IoFilter.NextFilter, org.apache.mina.common.IoSession, org.apache.mina.common.IoFilter.WriteRequest)
166      */
167     public void filterWrite(NextFilter nextFilter, IoSession session,
168             WriteRequest writeRequest) throws IOException JavaDoc {
169         if (!compressOutbound) {
170             nextFilter.filterWrite(session, writeRequest);
171             return;
172         }
173
174         if (session.containsAttribute(DISABLE_COMPRESSION_ONCE)) {
175             // Remove the marker attribute because it is temporary.
176 session.removeAttribute(DISABLE_COMPRESSION_ONCE);
177             nextFilter.filterWrite(session, writeRequest);
178             return;
179         }
180
181         Zlib deflater = (Zlib) session.getAttribute(DEFLATER);
182         if (deflater == null) {
183             throw new IllegalStateException JavaDoc();
184         }
185
186         ByteBuffer inBuffer = (ByteBuffer) writeRequest.getMessage();
187         if (!inBuffer.hasRemaining()) {
188             // Ignore empty buffers
189 nextFilter.filterWrite(session, writeRequest);
190         } else {
191             ByteBuffer outBuf = deflater.deflate(inBuffer);
192             inBuffer.release();
193             nextFilter.filterWrite(session, new WriteRequest(outBuf,
194                     writeRequest.getFuture()));
195         }
196     }
197
198     public void onPreAdd(IoFilterChain parent, String JavaDoc name,
199             NextFilter nextFilter) throws Exception JavaDoc {
200         if (parent.contains(CompressionFilter.class)) {
201             throw new IllegalStateException JavaDoc(
202                     "A filter chain cannot contain more than"
203                             + " one Stream Compression filter.");
204         }
205
206         Zlib deflater = new Zlib(compressionLevel, Zlib.MODE_DEFLATER);
207         Zlib inflater = new Zlib(compressionLevel, Zlib.MODE_INFLATER);
208
209         IoSession session = parent.getSession();
210
211         session.setAttribute(DEFLATER, deflater);
212         session.setAttribute(INFLATER, inflater);
213     }
214
215     /**
216      * Returns <tt>true</tt> if incoming data is being compressed.
217      */
218     public boolean isCompressInbound() {
219         return compressInbound;
220     }
221
222     /**
223      * Sets if incoming data has to be compressed.
224      */
225     public void setCompressInbound(boolean compressInbound) {
226         this.compressInbound = compressInbound;
227     }
228
229     /**
230      * Returns <tt>true</tt> if the filter is compressing data being written.
231      */
232     public boolean isCompressOutbound() {
233         return compressOutbound;
234     }
235
236     /**
237      * Set if outgoing data has to be compressed.
238      */
239     public void setCompressOutbound(boolean compressOutbound) {
240         this.compressOutbound = compressOutbound;
241     }
242
243     public void onPostRemove(IoFilterChain parent, String JavaDoc name,
244             NextFilter nextFilter) throws Exception JavaDoc {
245         super.onPostRemove(parent, name, nextFilter);
246         IoSession session = parent.getSession();
247         if (session == null) {
248             return;
249         }
250
251         Zlib inflater = (Zlib) session.getAttribute(INFLATER);
252         Zlib deflater = (Zlib) session.getAttribute(DEFLATER);
253         if (deflater != null) {
254             deflater.cleanUp();
255         }
256
257         if (inflater != null) {
258             inflater.cleanUp();
259         }
260     }
261 }
262
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