Package org.apache.poi.util
Class LZWDecompresser
- java.lang.Object
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- org.apache.poi.util.LZWDecompresser
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- Direct Known Subclasses:
CompressedRTF
,HDGFLZW
public abstract class LZWDecompresser extends java.lang.Object
This class provides common functionality for the various LZW implementations in the different file formats. It's currently used by HDGF and HMEF.Two good resources on LZW are: http://en.wikipedia.org/wiki/LZW http://marknelson.us/1989/10/01/lzw-data-compression/
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description byte[]
decompress(java.io.InputStream src)
Decompresses the given input stream, returning the array of bytes of the decompressed input.void
decompress(java.io.InputStream src, java.io.OutputStream res)
Perform a streaming decompression of the input.static int
getMaxRecordLength()
static void
setMaxRecordLength(int length)
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Field Detail
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DICT_SIZE
public static final int DICT_SIZE
the size of our dictionary- See Also:
- Constant Field Values
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DICT_MASK
public static final int DICT_MASK
the mask for calculating / wrapping dictionary offsets- See Also:
- Constant Field Values
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Method Detail
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setMaxRecordLength
public static void setMaxRecordLength(int length)
- Parameters:
length
- the max record length allowed for LZWDecompresser
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getMaxRecordLength
public static int getMaxRecordLength()
- Returns:
- the max record length allowed for LZWDecompresser
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decompress
public byte[] decompress(java.io.InputStream src) throws java.io.IOException
Decompresses the given input stream, returning the array of bytes of the decompressed input.- Throws:
java.io.IOException
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decompress
public void decompress(java.io.InputStream src, java.io.OutputStream res) throws java.io.IOException
Perform a streaming decompression of the input. Works by: 1) Reading a flag byte, the 8 bits of which tell you if the following 8 codes are compressed our un-compressed 2) Consider the 8 bits in turn 3) If the bit is set, the next code is un-compressed, so add it to the dictionary and output it 4) If the bit isn't set, then read in the length and start position in the dictionary, and output the bytes there 5) Loop until we've done all 8 bits, then read in the next flag byte- Throws:
java.io.IOException
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