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The Apache PDFBox library is an open source Java tool for working with PDF documents.
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.pdfbox.filter;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.pdfbox.cos.COSDictionary;
/**
* This is a filter for the RunLength Decoder.
*
* From the PDF Reference
*
* The RunLengthDecode filter decodes data that has been encoded in a simple
* byte-oriented format based on run length. The encoded data is a sequence of
* runs, where each run consists of a length byte followed by 1 to 128 bytes of data. If
* the length byte is in the range 0 to 127, the following length + 1 (1 to 128) bytes
* are copied literally during decompression. If length is in the range 129 to 255, the
* following single byte is to be copied 257 ? length (2 to 128) times during decompression.
* A length value of 128 denotes EOD.
*
* The compression achieved by run-length encoding depends on the input data. In
* the best case (all zeros), a compression of approximately 64:1 is achieved for long
* files. The worst case (the hexadecimal sequence 00 alternating with FF) results in
* an expansion of 127:128.
*
*
* @author Ben Litchfield
* @version $Revision: 1.6 $
*/
public class RunLengthDecodeFilter implements Filter
{
/**
* Log instance.
*/
private static final Log log = LogFactory.getLog(RunLengthDecodeFilter.class);
private static final int RUN_LENGTH_EOD = 128;
/**
* Constructor.
*/
public RunLengthDecodeFilter()
{
//default constructor
}
/**
* {@inheritDoc}
*/
public void decode( InputStream compressedData, OutputStream result, COSDictionary options, int filterIndex )
throws IOException
{
int dupAmount = -1;
byte[] buffer = new byte[128];
while( (dupAmount = compressedData.read()) != -1 && dupAmount != RUN_LENGTH_EOD )
{
if( dupAmount <= 127 )
{
int amountToCopy = dupAmount+1;
int compressedRead = 0;
while( amountToCopy > 0 )
{
compressedRead = compressedData.read( buffer, 0, amountToCopy );
result.write( buffer, 0, compressedRead );
amountToCopy -= compressedRead;
}
}
else
{
int dupByte = compressedData.read();
for( int i=0; i<257-dupAmount; i++ )
{
result.write( dupByte );
}
}
}
}
/**
* {@inheritDoc}
*/
public void encode( InputStream rawData, OutputStream result, COSDictionary options, int filterIndex )
throws IOException
{
log.warn( "RunLengthDecodeFilter.encode is not implemented yet, skipping this stream." );
}
}