Package org.apache.commons.compress.compressors.lzw

Class LZWInputStream

java.lang.Object

java.io.InputStream

org.apache.commons.compress.compressors.CompressorInputStream

org.apache.commons.compress.compressors.lzw.LZWInputStream

All Implemented Interfaces:

Closeable, AutoCloseable, InputStreamStatistics

Direct Known Subclasses:

ZCompressorInputStream

public abstract class LZWInputStream
extends CompressorInputStream
implements InputStreamStatistics

Generic LZW implementation. It is used internally for the Z decompressor and the Unshrinking Zip file compression method, but may be useful for third-party projects in implementing their own LZW variations.

Since:

1.10

This class is not thread-safe

Field Summary

Fields

Modifier and Type	Field	Description
protected static final int	DEFAULT_CODE_SIZE	Default code size in bits.
protected final BitInputStream	in	Input.
protected static final int	UNUSED_PREFIX	Unused marker.

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	LZWInputStream(InputStream inputStream, ByteOrder byteOrder)	Constructs a new instance.

Method Summary

Modifier and Type	Method	Description
protected abstract int	addEntry(int previousCode, byte character)	Add a new entry to the dictionary.
protected int	addEntry(int previousCode, byte character, int maxTableSize)	Adds a new entry if the maximum table size hasn't been exceeded and returns the new index.
protected int	addRepeatOfPreviousCode()	Add entry for repeat of previousCode we haven't added, yet.
void	close()
protected abstract int	decompressNextSymbol()	Reads the next code and expand it.
protected int	expandCodeToOutputStack(int code, boolean addedUnfinishedEntry)	Expands the entry with index code to the output stack and may create a new entry.
protected int	getClearCode()	Gets the clear code.
protected int	getCodeSize()	Gets the code size in bits.
long	getCompressedCount()	Gets the amount of raw or compressed bytes read by the stream.
protected int	getPrefix(int offset)	Gets the prefix at the given offset.
protected int	getPrefixesLength()	Gets the prefixes length.
protected int	getTableSize()	Gets the table size.
protected void	incrementCodeSize()	Increments the code size by one.
protected void	initializeTables(int maxCodeSize)	Initializes the arrays based on the maximum code size.
protected void	initializeTables(int maxCodeSize, int memoryLimiKiB)	Initializes the arrays based on the maximum code size.
int	read()
int	read(byte[] b, int off, int len)
protected int	readNextCode()	Reads the next code from the stream.
protected void	resetCodeSize()	Resets the code size to its default value.
protected void	resetPreviousCode()	Resets the previous code to its default value.
protected void	setClearCode(int codeSize)	Sets the clear code based on the code size.
protected void	setCodeSize(int codeSize)	Sets the code size in bits.
protected void	setPrefix(int offset, int value)	Sets the prefix at the given offset.
protected void	setTableSize(int tableSize)	Sets the table size.

Methods inherited from class org.apache.commons.compress.compressors.CompressorInputStream

count, count, getBytesRead, getCount, getUncompressedCount, pushedBackBytes

Methods inherited from class java.io.InputStream

available, mark, markSupported, read, reset, skip

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.commons.compress.utils.InputStreamStatistics

getUncompressedCount

Field Details

DEFAULT_CODE_SIZE

protected static final int DEFAULT_CODE_SIZE

Default code size in bits.

See Also:

• Constant Field Values

UNUSED_PREFIX

protected static final int UNUSED_PREFIX

Unused marker.

See Also:

• Constant Field Values

in

protected final BitInputStream in

Input.

Constructor Details

LZWInputStream

protected LZWInputStream(InputStream inputStream,
 ByteOrder byteOrder)

Constructs a new instance.

Parameters:

inputStream - The underlying input stream.

byteOrder - the input byte order.

Method Details

addEntry

protected abstract int addEntry(int previousCode,
 byte character)
                         throws IOException

Add a new entry to the dictionary.

Parameters:

previousCode - the previous code

character - the next character to append

Returns:

the new code

Throws:

IOException - on error

addEntry

protected int addEntry(int previousCode,
 byte character,
 int maxTableSize)

Adds a new entry if the maximum table size hasn't been exceeded and returns the new index.

Parameters:

previousCode - the previous code

character - the character to append

maxTableSize - the maximum table size

Returns:

the new code or -1 if maxTableSize has been reached already

addRepeatOfPreviousCode

protected int addRepeatOfPreviousCode()
                               throws IOException

Add entry for repeat of previousCode we haven't added, yet.

Returns:

new code for a repeat of the previous code or -1 if maxTableSize has been reached already

Throws:

IOException - on error

close

public void close()
           throws IOException

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Overrides:

close in class InputStream

Throws:

IOException

decompressNextSymbol

protected abstract int decompressNextSymbol()
                                     throws IOException

Reads the next code and expand it.

Returns:

the expanded next code, negative on EOF

Throws:

IOException - on error

expandCodeToOutputStack

protected int expandCodeToOutputStack(int code,
 boolean addedUnfinishedEntry)
                               throws IOException

Expands the entry with index code to the output stack and may create a new entry.

Parameters:

code - the code.

addedUnfinishedEntry - whether unfinished entries have been added.

Returns:

the new location of the output stack.

Throws:

IOException - if an I/O error occurs.

getClearCode

protected int getClearCode()

Gets the clear code.

Returns:

the clear code.

getCodeSize

protected int getCodeSize()

Gets the code size in bits.

Returns:

the code size in bits.

getCompressedCount

public long getCompressedCount()

Description copied from interface: InputStreamStatistics

Gets the amount of raw or compressed bytes read by the stream.

Specified by:

getCompressedCount in interface InputStreamStatistics

Returns:

the amount of raw or compressed bytes read by the stream.

Since:

1.17

getPrefix

protected int getPrefix(int offset)

Gets the prefix at the given offset.

Parameters:

offset - offset to query.

Returns:

the prefix at the given offset.

getPrefixesLength

protected int getPrefixesLength()

Gets the prefixes length.

Returns:

the prefixes length.

getTableSize

protected int getTableSize()

Gets the table size.

Returns:

the table size.

incrementCodeSize

protected void incrementCodeSize()

Increments the code size by one.

initializeTables

protected void initializeTables(int maxCodeSize)

Initializes the arrays based on the maximum code size.

Parameters:

maxCodeSize - maximum code size

Throws:

IllegalArgumentException - if maxCodeSize is out of bounds for prefixes and characters.

initializeTables

protected void initializeTables(int maxCodeSize,
 int memoryLimiKiB)
                         throws MemoryLimitException

Initializes the arrays based on the maximum code size. First checks that the estimated memory usage is below memoryLimitInKb

Parameters:

maxCodeSize - maximum code size

memoryLimiKiB - maximum allowed estimated memory usage in kibibytes (KiB).

Throws:

MemoryLimitException - if estimated memory usage is greater than memoryLimitKiB

IllegalArgumentException - if maxCodeSize is not bigger than 0

read

public int read()
         throws IOException

Specified by:

read in class InputStream

Throws:

IOException

read

public int read(byte[] b,
 int off,
 int len)
         throws IOException

Overrides:

read in class InputStream

Throws:

IOException

readNextCode

protected int readNextCode()
                    throws IOException

Reads the next code from the stream.

Returns:

the next code

Throws:

IOException - on error

resetCodeSize

protected void resetCodeSize()

Resets the code size to its default value.

resetPreviousCode

protected void resetPreviousCode()

Resets the previous code to its default value.

setClearCode

protected void setClearCode(int codeSize)

Sets the clear code based on the code size.

Parameters:

codeSize - code size

setCodeSize

protected void setCodeSize(int codeSize)

Sets the code size in bits.

Parameters:

codeSize - the code size in bits.

setPrefix

protected void setPrefix(int offset,
 int value)

Sets the prefix at the given offset.

Parameters:

offset - the target offset.

value - the new value.

setTableSize

protected void setTableSize(int tableSize)

Sets the table size.

Parameters:

tableSize - the new table size.