JavaTM 2 Platform Std. Ed. v1.4.2
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");
- See Also:
Inflater
Field Summary |
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 |
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 |
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. |
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
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.
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 bytesoff - the start offset of the datalen - 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 bytesoff - the start offset of the datalen - 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 dataoff - the start offset of the datalen - 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
Copyright 2003 Sun Microsystems, Inc. All rights reserved
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