Apache POI - Common 5.3.0 · org.apache.poi.util.LZWDecompresser

Field Summary

Modifier and Type	Field and Description
private final int	codeLengthIncrease How much to append to the code length in the stream to get the real code length?
private static final int	DEFAULT_MAX_RECORD_LENGTH
public static final int	DICT_MASK the mask for calculating / wrapping dictionary offsets
public static final int	DICT_SIZE the size of our dictionary
private final boolean	maskMeansCompressed Does the mask bit mean it's compressed or uncompressed?
private static int	MAX_RECORD_LENGTH
private final boolean	positionIsBigEndian Does the 12 bits of the position get stored in Little Endian or Big Endian form?

Constructor Summary

Access	Constructor and Description
protected	LZWDecompresser(boolean maskMeansCompressed, int codeLengthIncrease, boolean positionIsBigEndian)

Method Summary

Modifier and Type	Method and Description
protected abstract int	adjustDictionaryOffset(int offset) Adjusts the position offset if needed when looking something up in the dictionary.
public byte[]	decompress(InputStream src) Decompresses the given input stream, returning the array of bytes of the decompressed input.
public void	decompress(InputStream src, OutputStream res) Perform a streaming decompression of the input.
public static int	Returns: the max record length allowed for LZWDecompresser getMaxRecordLength()
protected abstract int	populateDictionary(byte[] dict) Populates the dictionary, and returns where in it to begin writing new codes.
public static void	setMaxRecordLength(int the max record length allowed for LZWDecompresser length)

Inherited from java.lang.Object:: clone equals finalize getClass hashCode notify notifyAll toString wait wait wait

Field Detail

codeLengthIncrease	back to summary
private final int codeLengthIncrease How much to append to the code length in the stream to get the real code length? Normally 2 or 3

DEFAULT_MAX_RECORD_LENGTH	back to summary
private static final int DEFAULT_MAX_RECORD_LENGTH

DICT_MASK	back to summary
public static final int DICT_MASK the mask for calculating / wrapping dictionary offsets

DICT_SIZE	back to summary
public static final int DICT_SIZE the size of our dictionary

maskMeansCompressed	back to summary
private final boolean maskMeansCompressed Does the mask bit mean it's compressed or uncompressed?

MAX_RECORD_LENGTH	back to summary
private static int MAX_RECORD_LENGTH

positionIsBigEndian	back to summary
private final boolean positionIsBigEndian Does the 12 bits of the position get stored in Little Endian or Big Endian form? This controls whether a pos+length of 0x12 0x34 becomes a position of 0x123 or 0x312

Constructor Detail

LZWDecompresser	back to summary
protected LZWDecompresser(boolean maskMeansCompressed, int codeLengthIncrease, boolean positionIsBigEndian)

Method Detail

adjustDictionaryOffset	back to summary
protected abstract int adjustDictionaryOffset(int offset) Adjusts the position offset if needed when looking something up in the dictionary.

decompress	back to summary
public byte[] decompress(InputStream src) throws IOException Decompresses the given input stream, returning the array of bytes of the decompressed input.

decompress	back to summary
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

decompress

back to summary

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

getMaxRecordLength	back to summary
public static int getMaxRecordLength() Returns:int the max record length allowed for LZWDecompresser

populateDictionary	back to summary
protected abstract int populateDictionary(byte[] dict) Populates the dictionary, and returns where in it to begin writing new codes. Generally, if the dictionary is pre-populated, then new codes should be placed at the end of that block. Equally, if the dictionary is left with all zeros, then usually the new codes can go in at the start.

setMaxRecordLength	back to summary
public static void setMaxRecordLength(int length) Parameters length:int the max record length allowed for LZWDecompresser