Package org.apache.pdfbox.filter

Class LZWFilter

java.lang.Object

org.apache.pdfbox.filter.Filter

org.apache.pdfbox.filter.LZWFilter

public class LZWFilter
extends Filter

This is the filter used for the LZWDecode filter.

Field Summary

Fields

Modifier and Type	Field	Description
static final long	CLEAR_TABLE	The LZW clear table code.
static final long	EOD	The LZW end of data code.
private static final List<byte[]>	INITIAL_CODE_TABLE
private static final org.apache.commons.logging.Log	LOG	Log instance.

Fields inherited from class org.apache.pdfbox.filter.Filter

SYSPROP_DEFLATELEVEL

Constructor Summary

Constructors

Constructor	Description
LZWFilter()

Method Summary

Modifier and Type	Method	Description
private static int	calculateChunk(int tabSize, boolean earlyChange)	Calculate the appropriate chunk size
private void	checkIndexBounds(List<byte[]> codeTable, long index, MemoryCacheImageInputStream in)
private static List<byte[]>	createCodeTable()	Init the code table with 1 byte entries and the EOD and CLEAR_TABLE markers.
private static List<byte[]>	createInitialCodeTable()
DecodeResult	decode(InputStream encoded, OutputStream decoded, COSDictionary parameters, int index)	Decodes data, producing the original non-encoded data.
private void	doLZWDecode(InputStream encoded, OutputStream decoded, boolean earlyChange)
protected void	encode(InputStream rawData, OutputStream encoded, COSDictionary parameters)
private static int	findPatternCode(List<byte[]> codeTable, byte[] pattern)	Find a matching pattern in the code table.

Methods inherited from class org.apache.pdfbox.filter.Filter

decode, encode, findImageReader, getCompressionLevel, getDecodeParams

Methods inherited from class java.lang.Object

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

Field Details

LOG

private static final org.apache.commons.logging.Log LOG

Log instance.

CLEAR_TABLE

public static final long CLEAR_TABLE

The LZW clear table code.

See Also:

• Constant Field Values

EOD

public static final long EOD

The LZW end of data code.

See Also:

• Constant Field Values

INITIAL_CODE_TABLE

private static final List<byte[]> INITIAL_CODE_TABLE

Constructor Details

LZWFilter

public LZWFilter()

Method Details

decode

public DecodeResult decode(InputStream encoded,
 OutputStream decoded,
 COSDictionary parameters,
 int index)
                    throws IOException

Decodes data, producing the original non-encoded data.

Specified by:

decode in class Filter

Parameters:

encoded - the encoded byte stream

decoded - the stream where decoded data will be written

parameters - the parameters used for decoding

index - the index to the filter being decoded

Returns:

repaired parameters dictionary, or the original parameters dictionary

Throws:

IOException - if the stream cannot be decoded

doLZWDecode

private void doLZWDecode(InputStream encoded,
 OutputStream decoded,
 boolean earlyChange)
                  throws IOException

Throws:

IOException

checkIndexBounds

private void checkIndexBounds(List<byte[]> codeTable,
 long index,
 MemoryCacheImageInputStream in)
                       throws IOException

Throws:

IOException

encode

protected void encode(InputStream rawData,
 OutputStream encoded,
 COSDictionary parameters)
               throws IOException

Specified by:

encode in class Filter

Throws:

IOException

findPatternCode

private static int findPatternCode(List<byte[]> codeTable,
 byte[] pattern)

Find a matching pattern in the code table.

Parameters:

codeTable - The LZW code table.

pattern - The pattern to be searched for.

Returns:

The index of the matching pattern or -1 if nothing is found.

createCodeTable

private static List<byte[]> createCodeTable()

Init the code table with 1 byte entries and the EOD and CLEAR_TABLE markers.

createInitialCodeTable

private static List<byte[]> createInitialCodeTable()

calculateChunk

private static int calculateChunk(int tabSize,
 boolean earlyChange)

Calculate the appropriate chunk size

Parameters:

tabSize - the size of the code table

earlyChange - true for early chunk increase

Returns:

a value between 9 and 12