java.util.zip

Class Deflater

java.lang.Object

java.util.zip.Deflater

public class Deflater
extends Object

This class provides support for general purpose compression using the popular ZLIB compression library. The ZLIB compression library was initially developed as part of the PNG graphics standard and is not protected by patents. It is fully described in the specifications at the java.util.zip package description.

The following code fragment demonstrates a trivial compression and decompression of a string using Deflater and Inflater.

 // Encode a String into bytes
 String inputString = "blahblahblah??";
 byte[] input = inputString.getBytes("UTF-8");

 // Compress the bytes
 byte[] output = new byte[100];
 Deflater compresser = new Deflater();
 compresser.setInput(input);
 compresser.finish();
 int compressedDataLength = compresser.deflate(output);

 // Decompress the bytes
 Inflater decompresser = new Inflater();
 decompresser.setInput(output, 0, compressedDataLength);
 byte[] result = new byte[100];
 int resultLength = decompresser.inflate(result);
 decompresser.end();

 // Decode the bytes into a String
 String outputString = new String(result, 0, resultLength, "UTF-8");
 

Version:

1.35, 05/03/00

Author:

David Connelly

See Also:

Inflater

Field Summary

Fields

Modifier and Type	Field and Description
static int	BEST_COMPRESSION Compression level for best compression.
static int	BEST_SPEED Compression level for fastest compression.
static int	DEFAULT_COMPRESSION Default compression level.
static int	DEFAULT_STRATEGY Default compression strategy.
static int	DEFLATED Compression method for the deflate algorithm (the only one currently supported).
static int	FILTERED Compression strategy best used for data consisting mostly of small values with a somewhat random distribution.
static int	HUFFMAN_ONLY Compression strategy for Huffman coding only.
static int	NO_COMPRESSION Compression level for no compression.

Constructor Summary

Constructors

Constructor and Description
Deflater() Creates a new compressor with the default compression level.
Deflater(int level) Creates a new compressor using the specified compression level.
Deflater(int level, boolean nowrap) Creates a new compressor using the specified compression level.

Method Summary

Methods

Modifier and Type	Method and Description
int	deflate(byte[] b) Fills specified buffer with compressed data.
int	deflate(byte[] b, int off, int len) Fills specified buffer with compressed data.
void	end() Closes the compressor and discards any unprocessed input.
protected void	finalize() Closes the compressor when garbage is collected.
void	finish() When called, indicates that compression should end with the current contents of the input buffer.
boolean	finished() Returns true if the end of the compressed data output stream has been reached.
int	getAdler() Returns the ADLER-32 value of the uncompressed data.
int	getTotalIn() Returns the total number of bytes input so far.
int	getTotalOut() Returns the total number of bytes output so far.
boolean	needsInput() Returns true if the input data buffer is empty and setInput() should be called in order to provide more input.
void	reset() Resets deflater so that a new set of input data can be processed.
void	setDictionary(byte[] b) Sets preset dictionary for compression.
void	setDictionary(byte[] b, int off, int len) Sets preset dictionary for compression.
void	setInput(byte[] b) Sets input data for compression.
void	setInput(byte[] b, int off, int len) Sets input data for compression.
void	setLevel(int level) Sets the current compression level to the specified value.
void	setStrategy(int strategy) Sets the compression strategy to the specified value.

Methods inherited from class java.lang.Object

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

Field Detail

DEFLATED

public static final int DEFLATED

Compression method for the deflate algorithm (the only one currently supported).

See Also:

Constant Field Values

NO_COMPRESSION

public static final int NO_COMPRESSION

Compression level for no compression.

See Also:

Constant Field Values

BEST_SPEED

public static final int BEST_SPEED

Compression level for fastest compression.

See Also:

Constant Field Values

BEST_COMPRESSION

public static final int BEST_COMPRESSION

Compression level for best compression.

See Also:

Constant Field Values

DEFAULT_COMPRESSION

public static final int DEFAULT_COMPRESSION

Default compression level.

See Also:

Constant Field Values

FILTERED

public static final int FILTERED

Compression strategy best used for data consisting mostly of small values with a somewhat random distribution. Forces more Huffman coding and less string matching.

See Also:

Constant Field Values

HUFFMAN_ONLY

public static final int HUFFMAN_ONLY

Compression strategy for Huffman coding only.

See Also:

Constant Field Values

DEFAULT_STRATEGY

public static final int DEFAULT_STRATEGY

Default compression strategy.

See Also:

Constant Field Values

Constructor Detail

Deflater

public Deflater(int level,
        boolean nowrap)

Creates a new compressor using the specified compression level. If 'nowrap' is true then the ZLIB header and checksum fields will not be used in order to support the compression format used in both GZIP and PKZIP.

Parameters:

level - the compression level (0-9)

nowrap - if true then use GZIP compatible compression

Deflater

public Deflater(int level)

Creates a new compressor using the specified compression level. Compressed data will be generated in ZLIB format.

Parameters:

level - the compression level (0-9)

Deflater

public Deflater()

Creates a new compressor with the default compression level. Compressed data will be generated in ZLIB format.

Method Detail

setInput

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

Sets input data for compression. This should be called whenever needsInput() returns true indicating that more input data is required.

Parameters:

b - the input data bytes

off - the start offset of the data

len - the length of the data

See Also:

needsInput()

setInput

public void setInput(byte[] b)

Sets input data for compression. This should be called whenever needsInput() returns true indicating that more input data is required.

Parameters:

b - the input data bytes

See Also:

needsInput()

setDictionary

public void setDictionary(byte[] b,
                 int off,
                 int len)

Sets preset dictionary for compression. A preset dictionary is used when the history buffer can be predetermined. When the data is later uncompressed with Inflater.inflate(), Inflater.getAdler() can be called in order to get the Adler-32 value of the dictionary required for decompression.

Parameters:

b - the dictionary data bytes

off - the start offset of the data

len - the length of the data

See Also:

Inflater.inflate(byte[], int, int), Inflater.getAdler()

setDictionary

public void setDictionary(byte[] b)

Sets preset dictionary for compression. A preset dictionary is used when the history buffer can be predetermined. When the data is later uncompressed with Inflater.inflate(), Inflater.getAdler() can be called in order to get the Adler-32 value of the dictionary required for decompression.

Parameters:

b - the dictionary data bytes

See Also:

Inflater.inflate(byte[], int, int), Inflater.getAdler()

setStrategy

public void setStrategy(int strategy)

Sets the compression strategy to the specified value.

Parameters:

strategy - the new compression strategy

Throws:

IllegalArgumentException - if the compression strategy is invalid

setLevel

public void setLevel(int level)

Sets the current compression level to the specified value.

Parameters:

level - the new compression level (0-9)

Throws:

IllegalArgumentException - if the compression level is invalid

needsInput

public boolean needsInput()

Returns true if the input data buffer is empty and setInput() should be called in order to provide more input.

Returns:

true if the input data buffer is empty and setInput() should be called in order to provide more input

finish

public void finish()

When called, indicates that compression should end with the current contents of the input buffer.

finished

public boolean finished()

Returns true if the end of the compressed data output stream has been reached.

Returns:

true if the end of the compressed data output stream has been reached

deflate

public int deflate(byte[] b,
          int off,
          int len)

Fills specified buffer with compressed data. Returns actual number of bytes of compressed data. A return value of 0 indicates that needsInput() should be called in order to determine if more input data is required.

Parameters:

b - the buffer for the compressed data

off - the start offset of the data

len - the maximum number of bytes of compressed data

Returns:

the actual number of bytes of compressed data

deflate

public int deflate(byte[] b)

Fills specified buffer with compressed data. Returns actual number of bytes of compressed data. A return value of 0 indicates that needsInput() should be called in order to determine if more input data is required.

Parameters:

b - the buffer for the compressed data

Returns:

the actual number of bytes of compressed data

getAdler

public int getAdler()

Returns the ADLER-32 value of the uncompressed data.

Returns:

the ADLER-32 value of the uncompressed data

getTotalIn

public int getTotalIn()

Returns the total number of bytes input so far.

Returns:

the total number of bytes input so far

getTotalOut

public int getTotalOut()

Returns the total number of bytes output so far.

Returns:

the total number of bytes output so far

reset

public void reset()

Resets deflater so that a new set of input data can be processed. Keeps current compression level and strategy settings.

end

public void end()

Closes the compressor and discards any unprocessed input. This method should be called when the compressor is no longer being used, but will also be called automatically by the finalize() method. Once this method is called, the behavior of the Deflater object is undefined.

finalize

protected void finalize()

Closes the compressor when garbage is collected.

Overrides:

finalize in class Object