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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.
|
long
|
getBytesRead
()
Returns the total number of uncompressed bytes input so far.
|
long
|
getBytesWritten
()
Returns the total number of compressed bytes output so far.
|
int
|
getTotalIn
()
Returns the total number of uncompressed bytes input so far.
|
int
|
getTotalOut
()
Returns the total number of compressed 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.
|
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 uncompressed bytes input so far.
Since the number of bytes may be greater than Integer.MAX_VALUE, the
getBytesRead()
method is now the preferred means of obtaining this information.
-
-
Returns:
-
the total number of uncompressed bytes input so far
getBytesRead
public long getBytesRead ()
-
Returns the total number of uncompressed bytes input so far.
-
-
Returns:
-
the total (non-negative) number of uncompressed bytes input so far
getTotalOut
public int getTotalOut ()
-
Returns the total number of compressed bytes output so far.
Since the number of bytes may be greater than Integer.MAX_VALUE, the
getBytesWritten()
method is now the preferred means of obtaining this information.
-
-
Returns:
-
the total number of compressed bytes output so far
getBytesWritten
public long getBytesWritten ()
-
Returns the total number of compressed bytes output so far.
-
-
Returns:
-
the total (non-negative) number of compressed bytes output so far
reset
The following code fragment demonstrates a trivial compression and decompression of a string using
Deflater
and
Inflater
.
public void reset ()
// 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");
-
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:
See Also:
-
finalize
Inflater
in class
Object
-
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.
|
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
-