Package org.apache.poi.util

Class LZWDecompresser

java.lang.Object

org.apache.poi.util.LZWDecompresser

Direct Known Subclasses:

CompressedRTF, HDGFLZW

public abstract class LZWDecompresser
extends 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/

Field Summary

Fields

Modifier and Type	Field	Description
static final int	DICT_MASK	the mask for calculating / wrapping dictionary offsets
static final int	DICT_SIZE	the size of our dictionary

Method Summary

Modifier and Type	Method	Description
byte[]	decompress(InputStream src)	Decompresses the given input stream, returning the array of bytes of the decompressed input.
void	decompress(InputStream src, OutputStream res)	Perform a streaming decompression of the input.
static int	getMaxRecordLength()
static void	setMaxRecordLength(int length)

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

DICT_SIZE

public static final int DICT_SIZE

the size of our dictionary

See Also:

• Constant Field Values

DICT_MASK

public static final int DICT_MASK

the mask for calculating / wrapping dictionary offsets

See Also:

• Constant Field Values

Method Details

setMaxRecordLength

public static void setMaxRecordLength(int length)

Parameters:

length - the max record length allowed for LZWDecompresser

getMaxRecordLength

public static int getMaxRecordLength()

Returns:

the max record length allowed for LZWDecompresser

decompress

public byte[] decompress(InputStream src)
                  throws IOException

Decompresses the given input stream, returning the array of bytes of the decompressed input.

Throws:

IOException

decompress

public void decompress(InputStream src,
 OutputStream res)
                throws 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:

IOException