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.
int
getTotalIn()
Gets the number of input bytes processed so far.
int
getTotalOut()
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.

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

BEST_COMPRESSION

public static final int BEST_COMPRESSION
The best and slowest compression level. This tries to find very long and distant string repetitions.
Field Value:
9

BEST_SPEED

public static final int BEST_SPEED
The worst but fastest compression level.
Field Value:
1

DEFAULT_COMPRESSION

public static final int DEFAULT_COMPRESSION
The default compression level.
Field Value:
-1

DEFAULT_STRATEGY

public static final int DEFAULT_STRATEGY
The default strategy.
Field Value:
0

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.
Field Value:
8

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.
Field Value:
1

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.
Field Value:
2

NO_COMPRESSION

public static final int NO_COMPRESSION
This level won't compress at all but output uncompressed blocks.
Field Value:
0

Constructor Details

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 Details

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.
Overrides:
finalize in interface 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

getTotalIn

public int getTotalIn()
Gets the number of input bytes processed so far.

getTotalOut

public int getTotalOut()
Gets the number of output bytes so far.

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.

Deflater.java - Compress a data stream Copyright (C) 1999, 2000, 2001, 2004, 2005 Free Software Foundation, Inc. This file is part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.