java.util.zip

Class Deflater

public class Deflater extends Object

This is the Deflater class. The deflater class compresses input with the deflate algorithm described in RFC 1951. It has several compression levels and three different strategies described below. This class is not thread safe. This is inherent in the API, due to the split of deflate and setInput.

Field Summary
static int	BEST_COMPRESSION The best and slowest compression level.
static int	BEST_SPEED The worst but fastest compression level.
static int	DEFAULT_COMPRESSION The default compression level.
static int	DEFAULT_STRATEGY The default strategy.
static int	DEFLATED The compression method.
static int	FILTERED This strategy will only allow longer string repetitions.
static int	HUFFMAN_ONLY This strategy will not look for string repetitions at all.
static int	NO_COMPRESSION This level won't compress at all but output uncompressed blocks.

Constructor Summary
	Deflater() Creates a new deflater with default compression level.
	Deflater(int lvl) Creates a new deflater with given compression level.
	Deflater(int lvl, boolean nowrap) Creates a new deflater with given compression level.

Method Summary
int	deflate(byte[] output) Deflates the current input block to the given array.
int	deflate(byte[] output, int offset, int length) Deflates the current input block to the given array.
void	end() Frees all objects allocated by the compressor.
protected void	finalize() Finalizes this object.
void	finish() Finishes the deflater with the current input block.
boolean	finished() Returns true iff the stream was finished and no more output bytes are available.
int	getAdler() Gets the current adler checksum of the data that was processed so far.
long	getBytesRead() Gets the number of input bytes processed so far.
long	getBytesWritten() Gets the number of output bytes so far.
boolean	needsInput() Returns true, if the input buffer is empty.
void	reset() Resets the deflater.
void	setDictionary(byte[] dict) Sets the dictionary which should be used in the deflate process.
void	setDictionary(byte[] dict, int offset, int length) Sets the dictionary which should be used in the deflate process.
void	setInput(byte[] input) Sets the data which should be compressed next.
void	setInput(byte[] input, int off, int len) Sets the data which should be compressed next.
void	setLevel(int lvl) Sets the compression level.
void	setStrategy(int stgy) Sets the compression strategy.

Field Detail

BEST_COMPRESSION

public static final int BEST_COMPRESSION

The best and slowest compression level. This tries to find very long and distant string repetitions.

BEST_SPEED

public static final int BEST_SPEED

The worst but fastest compression level.

DEFAULT_COMPRESSION

public static final int DEFAULT_COMPRESSION

The default compression level.

DEFAULT_STRATEGY

public static final int DEFAULT_STRATEGY

The default strategy.

DEFLATED

public static final int DEFLATED

The compression method. This is the only method supported so far. There is no need to use this constant at all.

FILTERED

public static final int FILTERED

This strategy will only allow longer string repetitions. It is useful for random data with a small character set.

HUFFMAN_ONLY

public static final int HUFFMAN_ONLY

This strategy will not look for string repetitions at all. It only encodes with Huffman trees (which means, that more common characters get a smaller encoding.

NO_COMPRESSION

public static final int NO_COMPRESSION

This level won't compress at all but output uncompressed blocks.

Constructor Detail

Deflater

public Deflater()

Creates a new deflater with default compression level.

Deflater

public Deflater(int lvl)

Creates a new deflater with given compression level.

Parameters: lvl the compression level, a value between NO_COMPRESSION and BEST_COMPRESSION, or DEFAULT_COMPRESSION.

Throws: IllegalArgumentException if lvl is out of range.

Deflater

public Deflater(int lvl, boolean nowrap)

Creates a new deflater with given compression level.

Parameters: lvl the compression level, a value between NO_COMPRESSION and BEST_COMPRESSION. nowrap true, iff we should suppress the deflate header at the beginning and the adler checksum at the end of the output. This is useful for the GZIP format.

Throws: IllegalArgumentException if lvl is out of range.

Method Detail

deflate

public int deflate(byte[] output)

Deflates the current input block to the given array. It returns the number of bytes compressed, or 0 if either needsInput() or finished() returns true or length is zero.

Parameters: output the buffer where to write the compressed data.

deflate

public int deflate(byte[] output, int offset, int length)

Deflates the current input block to the given array. It returns the number of bytes compressed, or 0 if either needsInput() or finished() returns true or length is zero.

Parameters: output the buffer where to write the compressed data. offset the offset into the output array. length the maximum number of bytes that may be written.

Throws: IllegalStateException if end() was called. IndexOutOfBoundsException if offset and/or length don't match the array length.

end

public void end()

Frees all objects allocated by the compressor. There's no reason to call this, since you can just rely on garbage collection. Exists only for compatibility against Sun's JDK, where the compressor allocates native memory. If you call any method (even reset) afterwards the behaviour is undefined.

finalize

protected void finalize()

Finalizes this object.

finish

public void finish()

Finishes the deflater with the current input block. It is an error to give more input after this method was called. This method must be called to force all bytes to be flushed.

finished

public boolean finished()

Returns true iff the stream was finished and no more output bytes are available.

getAdler

public int getAdler()

Gets the current adler checksum of the data that was processed so far.

getBytesRead

public long getBytesRead()

Gets the number of input bytes processed so far.

Since: 1.5

getBytesWritten

public long getBytesWritten()

Gets the number of output bytes so far.

Since: 1.5

needsInput

public boolean needsInput()

Returns true, if the input buffer is empty. You should then call setInput().
NOTE: This method can also return true when the stream was finished.

reset

public void reset()

Resets the deflater. The deflater acts afterwards as if it was just created with the same compression level and strategy as it had before.

setDictionary

public void setDictionary(byte[] dict)

Sets the dictionary which should be used in the deflate process. This call is equivalent to

setDictionary(dict, 0,
 dict.length)

Parameters: dict the dictionary.

Throws: IllegalStateException if setInput () or deflate () were already called or another dictionary was already set.

setDictionary

public void setDictionary(byte[] dict, int offset, int length)

Sets the dictionary which should be used in the deflate process. The dictionary should be a byte array containing strings that are likely to occur in the data which should be compressed. The dictionary is not stored in the compressed output, only a checksum. To decompress the output you need to supply the same dictionary again.

Parameters: dict the dictionary. offset an offset into the dictionary. length the length of the dictionary.

Throws: IllegalStateException if setInput () or deflate () were already called or another dictionary was already set.

setInput

public void setInput(byte[] input)

Sets the data which should be compressed next. This should be only called when needsInput indicates that more input is needed. If you call setInput when needsInput() returns false, the previous input that is still pending will be thrown away. The given byte array should not be changed, before needsInput() returns true again. This call is equivalent to setInput(input, 0, input.length).

Parameters: input the buffer containing the input data.

Throws: IllegalStateException if the buffer was finished() or ended().

setInput

public void setInput(byte[] input, int off, int len)

Sets the data which should be compressed next. This should be only called when needsInput indicates that more input is needed. The given byte array should not be changed, before needsInput() returns true again.

Parameters: input the buffer containing the input data. off the start of the data. len the length of the data.

Throws: IllegalStateException if the buffer was finished() or ended() or if previous input is still pending.

setLevel

public void setLevel(int lvl)

Sets the compression level. There is no guarantee of the exact position of the change, but if you call this when needsInput is true the change of compression level will occur somewhere near before the end of the so far given input.

Parameters: lvl the new compression level.

setStrategy

public void setStrategy(int stgy)

Sets the compression strategy. Strategy is one of DEFAULT_STRATEGY, HUFFMAN_ONLY and FILTERED. For the exact position where the strategy is changed, the same as for setLevel() applies.

Parameters: stgy the new compression strategy.