org.apache.poi.hdgf

Class HDGFLZW

java.lang.Object

org.apache.poi.util.LZWDecompresser

org.apache.poi.hdgf.HDGFLZW

public class HDGFLZW
extends LZWDecompresser

A decoder for the crazy LZW implementation used in Visio. According to VSDump, "it's a slightly perverted version of LZW compression, with inverted meaning of flag byte and 0xFEE as an 'initial shift'". It uses 12 bit codes (http://www.gnome.ru/projects/vsdump_en.html) Two good resources on LZW are: http://en.wikipedia.org/wiki/LZW http://marknelson.us/1989/10/01/lzw-data-compression/

Field Summary

Fields inherited from class org.apache.poi.util.LZWDecompresser

DICT_MASK, DICT_SIZE

Constructor Summary

Constructors

Constructor and Description
HDGFLZW()

Method Summary

Modifier and Type	Method and Description
protected int	adjustDictionaryOffset(int pntr) We have a slight shift by 18 bytes
byte[]	compress(InputStream src) Compress the given input stream, returning the array of bytes of the compressed input
void	compress(InputStream src, OutputStream res) Performs the Visio compatible streaming LZW compression.
protected int	populateDictionary(byte[] dict) We want an empty dictionary, so do nothing

Methods inherited from class org.apache.poi.util.LZWDecompresser

decompress, decompress, getMaxRecordLength, setMaxRecordLength

Methods inherited from class java.lang.Object

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

Constructor Detail

HDGFLZW

public HDGFLZW()

Method Detail

compress

public byte[] compress(InputStream src)
                throws IOException

Compress the given input stream, returning the array of bytes of the compressed input

Parameters:

src - the compression source byte

Returns:

the compressed stream as bytes

Throws:

IOException - when the InputStream can't be read

adjustDictionaryOffset

protected int adjustDictionaryOffset(int pntr)

We have a slight shift by 18 bytes

Specified by:

adjustDictionaryOffset in class LZWDecompresser

populateDictionary

protected int populateDictionary(byte[] dict)

We want an empty dictionary, so do nothing

Specified by:

populateDictionary in class LZWDecompresser

compress

public void compress(InputStream src,
                     OutputStream res)
              throws IOException

Performs the Visio compatible streaming LZW compression.

Parameters:

src - the input bytes for the compression

res - the OutputStream which receives the compressed bytes

Throws:

IOException - when the InputStream can't be read or the OutputStream can't be written to