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Java > Open Source Codes > org > pdfbox > filter > RunLengthDecodeFilter


1 /**
2  * Copyright (c) 2004, www.pdfbox.org
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions are met:
7  *
8  * 1. Redistributions of source code must retain the above copyright notice,
9  * this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright notice,
11  * this list of conditions and the following disclaimer in the documentation
12  * and/or other materials provided with the distribution.
13  * 3. Neither the name of pdfbox; nor the names of its
14  * contributors may be used to endorse or promote products derived from this
15  * software without specific prior written permission.
16  *
17  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
18  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
20  * DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY
21  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
22  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
23  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
24  * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
26  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27  *
28  * http://www.pdfbox.org
29  *
30  */
31 package org.pdfbox.filter;
32
33 import java.io.IOException JavaDoc;
34 import java.io.InputStream JavaDoc;
35 import java.io.OutputStream JavaDoc;
36
37 import org.pdfbox.cos.COSDictionary;
38
39 /**
40  * This is a filter for the RunLength Decoder.
41  *
42  * From the PDF Reference
43  * <pre>
44  * The RunLengthDecode filter decodes data that has been encoded in a simple
45  * byte-oriented format based on run length. The encoded data is a sequence of
46  * runs, where each run consists of a length byte followed by 1 to 128 bytes of data. If
47  * the length byte is in the range 0 to 127, the following length + 1 (1 to 128) bytes
48  * are copied literally during decompression. If length is in the range 129 to 255, the
49  * following single byte is to be copied 257 ? length (2 to 128) times during decompression.
50  * A length value of 128 denotes EOD.
51  *
52  * The compression achieved by run-length encoding depends on the input data. In
53  * the best case (all zeros), a compression of approximately 64:1 is achieved for long
54  * files. The worst case (the hexadecimal sequence 00 alternating with FF) results in
55  * an expansion of 127:128.
56  * </pre>
57  *
58  * @author <a HREF="mailto:ben@benlitchfield.com">Ben Litchfield</a>
59  * @version $Revision: 1.5 $
60  */
61 public class RunLengthDecodeFilter implements Filter
62 {
63     private static final int RUN_LENGTH_EOD = 128;
64
65     /**
66      * Constructor.
67      */
68     public RunLengthDecodeFilter()
69     {
70         //default constructor
71 }
72
73     /**
74      * This will decode some compressed data.
75      *
76      * @param compressedData The compressed byte stream.
77      * @param result The place to write the uncompressed byte stream.
78      * @param options The options to use to encode the data.
79      *
80      * @throws IOException If there is an error decompressing the stream.
81      */
82     public void decode( InputStream JavaDoc compressedData, OutputStream JavaDoc result, COSDictionary options ) throws IOException JavaDoc
83     {
84         int dupAmount = -1;
85         byte[] buffer = new byte[128];
86         while( (dupAmount = compressedData.read()) != -1 && dupAmount != RUN_LENGTH_EOD )
87         {
88             if( dupAmount <= 127 )
89             {
90                 int amountToCopy = dupAmount+1;
91                 int compressedRead = 0;
92                 while( amountToCopy > 0 )
93                 {
94                     compressedRead = compressedData.read( buffer, 0, amountToCopy );
95                     result.write( buffer, 0, compressedRead );
96                     amountToCopy -= compressedRead;
97                 }
98             }
99             else
100             {
101                 int dupByte = compressedData.read();
102                 for( int i=0; i<257-dupAmount; i++ )
103                 {
104                     result.write( dupByte );
105                 }
106             }
107         }
108     }
109
110      /**
111      * This will encode some data.
112      *
113      * @param rawData The raw data to encode.
114      * @param result The place to write to encoded results to.
115      * @param options The options to use to encode the data.
116      *
117      * @throws IOException If there is an error compressing the stream.
118      */
119     public void encode( InputStream JavaDoc rawData, OutputStream JavaDoc result, COSDictionary options ) throws IOException JavaDoc
120     {
121         System.err.println( "Warning: RunLengthDecodeFilter.encode is not implemented yet, skipping this stream." );
122     }
123 }
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