Class 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.

This class deflates sequences of bytes into ZLIB compressed data format. The input byte sequence is provided in either byte array or byte buffer, via one of the setInput() methods. The output byte sequence is written to the output byte array or byte buffer passed to the deflate() methods.

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

try {
    // 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);
    compresser.end();

    // 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");
} catch (java.io.UnsupportedEncodingException ex) {
    // handle
} catch (java.util.zip.DataFormatException ex) {
    // handle
}
API Note:
To release resources used by this Deflater, the end() method should be called explicitly. Subclasses are responsible for the cleanup of resources acquired by the subclass. Subclasses that override finalize() in order to perform cleanup should be modified to use alternative cleanup mechanisms such as Cleaner and remove the overriding finalize method.
Implementation Requirements:
If this Deflater has been subclassed and the end method has been overridden, the end method will be called by the finalization when the deflater is unreachable. But the subclasses should not depend on this specific implementation; the finalization is not reliable and the finalize method is deprecated to be removed.
Since:
1.1
See Also:
Inflater

Field Summary

Fields
Modifier and Type Field 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 FULL_FLUSH

Compression flush mode used to flush out all pending output and reset the deflater.
static int HUFFMAN_ONLY

Compression strategy for Huffman coding only.
static int NO_COMPRESSION

Compression level for no compression.
static int NO_FLUSH

Compression flush mode used to achieve best compression result.
static int SYNC_FLUSH

Compression flush mode used to flush out all pending output; may degrade compression for some compression algorithms.

Constructor Summary

Constructors
Constructor 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

All Methods Instance Methods Concrete Methods Deprecated Methods
Modifier and Type Method Description
int deflate​(byte[] output)

Compresses the input data and fills specified buffer with compressed data.
int deflate​(byte[] output, int off, int len)

Compresses the input data and fills specified buffer with compressed data.
int deflate​(byte[] output, int off, int len, int flush)

Compresses the input data and fills the specified buffer with compressed data.
int deflate​(ByteBuffer output)

Compresses the input data and fills specified buffer with compressed data.
int deflate​(ByteBuffer output, int flush)

Compresses the input data and fills the specified buffer with compressed data.
void end()

Closes the compressor and discards any unprocessed input.
protected void finalize()

Deprecated, for removal: This API element is subject to removal in a future version.

The finalize method has been deprecated and will be removed.
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 no data remains in the input buffer.
void reset()

Resets deflater so that a new set of input data can be processed.
void setDictionary​(byte[] dictionary)

Sets preset dictionary for compression.
void setDictionary​(byte[] dictionary, int off, int len)

Sets preset dictionary for compression.
void setDictionary​(ByteBuffer dictionary)

Sets preset dictionary for compression.
void setInput​(byte[] input)

Sets input data for compression.
void setInput​(byte[] input, int off, int len)

Sets input data for compression.
void setInput​(ByteBuffer input)

Sets input data for compression.
void setLevel​(int level)

Sets the compression level to the specified value.
void setStrategy​(int strategy)

Sets the compression strategy to the specified value.

Methods declared in 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

NO_FLUSH

public static final int NO_FLUSH

Compression flush mode used to achieve best compression result.

Since:
1.7
See Also:
deflate(byte[], int, int, int), Constant Field Values

SYNC_FLUSH

public static final int SYNC_FLUSH

Compression flush mode used to flush out all pending output; may degrade compression for some compression algorithms.

Since:
1.7
See Also:
deflate(byte[], int, int, int), Constant Field Values

FULL_FLUSH

public static final int FULL_FLUSH

Compression flush mode used to flush out all pending output and reset the deflater. Using this mode too often can seriously degrade compression.

Since:
1.7
See Also:
deflate(byte[], int, int, int), 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[] input,
                     int off,
                     int len)

Sets input data for compression.

One of the setInput() methods should be called whenever needsInput() returns true indicating that more input data is required.

Parameters:
input - 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[] input)

Sets input data for compression.

One of the setInput() methods should be called whenever needsInput() returns true indicating that more input data is required.

Parameters:
input - the input data bytes
See Also:
needsInput()

setInput

public void setInput​(ByteBuffer input)

Sets input data for compression.

One of the setInput() methods should be called whenever needsInput() returns true indicating that more input data is required.

The given buffer's position will be advanced as deflate operations are performed, up to the buffer's limit. The input buffer may be modified (refilled) between deflate operations; doing so is equivalent to creating a new buffer and setting it with this method.

Modifying the input buffer's contents, position, or limit concurrently with an deflate operation will result in undefined behavior, which may include incorrect operation results or operation failure.

Parameters:
input - the input data bytes
Since:
11
See Also:
needsInput()

setDictionary

public void setDictionary​(byte[] dictionary,
                          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:
dictionary - 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[] dictionary)

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:
dictionary - the dictionary data bytes
See Also:
Inflater.inflate(byte[], int, int), Inflater.getAdler()

setDictionary

public void setDictionary​(ByteBuffer dictionary)

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.

The bytes in given byte buffer will be fully consumed by this method. On return, its position will equal its limit.

Parameters:
dictionary - 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.

If the compression strategy is changed, the next invocation of deflate will compress the input available so far with the old strategy (and may be flushed); the new strategy will take effect only after that invocation.

Parameters:
strategy - the new compression strategy
Throws:
IllegalArgumentException - if the compression strategy is invalid

setLevel

public void setLevel​(int level)

Sets the compression level to the specified value.

If the compression level is changed, the next invocation of deflate will compress the input available so far with the old level (and may be flushed); the new level will take effect only after that invocation.

Parameters:
level - the new compression level (0-9)
Throws:
IllegalArgumentException - if the compression level is invalid

needsInput

public boolean needsInput()

Returns true if no data remains in the input buffer. This can be used to determine if one of the setInput() methods 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[] output,
                   int off,
                   int len)

Compresses the input data and 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.

This method uses NO_FLUSH as its compression flush mode. An invocation of this method of the form deflater.deflate(b, off, len) yields the same result as the invocation of deflater.deflate(b, off, len, Deflater.NO_FLUSH).

Parameters:
output - 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 written to the output buffer

deflate

public int deflate​(byte[] output)

Compresses the input data and 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.

This method uses NO_FLUSH as its compression flush mode. An invocation of this method of the form deflater.deflate(b) yields the same result as the invocation of deflater.deflate(b, 0, b.length, Deflater.NO_FLUSH).

Parameters:
output - the buffer for the compressed data
Returns:
the actual number of bytes of compressed data written to the output buffer

deflate

public int deflate​(ByteBuffer output)

Compresses the input data and 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.

This method uses NO_FLUSH as its compression flush mode. An invocation of this method of the form deflater.deflate(output) yields the same result as the invocation of deflater.deflate(output, Deflater.NO_FLUSH).

Parameters:
output - the buffer for the compressed data
Returns:
the actual number of bytes of compressed data written to the output buffer
Since:
11

deflate

public int deflate​(byte[] output,
                   int off,
                   int len,
                   int flush)

Compresses the input data and fills the specified buffer with compressed data. Returns actual number of bytes of data compressed.

Compression flush mode is one of the following three modes:

  • NO_FLUSH: allows the deflater to decide how much data to accumulate, before producing output, in order to achieve the best compression (should be used in normal use scenario). A return value of 0 in this flush mode indicates that needsInput() should be called in order to determine if more input data is required.
  • SYNC_FLUSH: all pending output in the deflater is flushed, to the specified output buffer, so that an inflater that works on compressed data can get all input data available so far (In particular the needsInput() returns true after this invocation if enough output space is provided). Flushing with SYNC_FLUSH may degrade compression for some compression algorithms and so it should be used only when necessary.
  • FULL_FLUSH: all pending output is flushed out as with SYNC_FLUSH. The compression state is reset so that the inflater that works on the compressed output data can restart from this point if previous compressed data has been damaged or if random access is desired. Using FULL_FLUSH too often can seriously degrade compression.

In the case of FULL_FLUSH or SYNC_FLUSH, if the return value is len, the space available in output buffer b, this method should be invoked again with the same flush parameter and more output space. Make sure that len is greater than 6 to avoid flush marker (5 bytes) being repeatedly output to the output buffer every time this method is invoked.

If the setInput(ByteBuffer) method was called to provide a buffer for input, the input buffer's position will be advanced by the number of bytes consumed by this operation.

Parameters:
output - the buffer for the compressed data
off - the start offset of the data
len - the maximum number of bytes of compressed data
flush - the compression flush mode
Returns:
the actual number of bytes of compressed data written to the output buffer
Throws:
IllegalArgumentException - if the flush mode is invalid
Since:
1.7

deflate

public int deflate​(ByteBuffer output,
                   int flush)

Compresses the input data and fills the specified buffer with compressed data. Returns actual number of bytes of data compressed.

Compression flush mode is one of the following three modes:

  • NO_FLUSH: allows the deflater to decide how much data to accumulate, before producing output, in order to achieve the best compression (should be used in normal use scenario). A return value of 0 in this flush mode indicates that needsInput() should be called in order to determine if more input data is required.
  • SYNC_FLUSH: all pending output in the deflater is flushed, to the specified output buffer, so that an inflater that works on compressed data can get all input data available so far (In particular the needsInput() returns true after this invocation if enough output space is provided). Flushing with SYNC_FLUSH may degrade compression for some compression algorithms and so it should be used only when necessary.
  • FULL_FLUSH: all pending output is flushed out as with SYNC_FLUSH. The compression state is reset so that the inflater that works on the compressed output data can restart from this point if previous compressed data has been damaged or if random access is desired. Using FULL_FLUSH too often can seriously degrade compression.

In the case of FULL_FLUSH or SYNC_FLUSH, if the return value is equal to the remaining space of the buffer, this method should be invoked again with the same flush parameter and more output space. Make sure that the buffer has at least 6 bytes of remaining space to avoid the flush marker (5 bytes) being repeatedly output to the output buffer every time this method is invoked.

On success, the position of the given output byte buffer will be advanced by as many bytes as were produced by the operation, which is equal to the number returned by this method.

If the setInput(ByteBuffer) method was called to provide a buffer for input, the input buffer's position will be advanced by the number of bytes consumed by this operation.

Parameters:
output - the buffer for the compressed data
flush - the compression flush mode
Returns:
the actual number of bytes of compressed data written to the output buffer
Throws:
IllegalArgumentException - if the flush mode is invalid
Since:
11

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
Since:
1.5

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
Since:
1.5

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. Once this method is called, the behavior of the Deflater object is undefined.

finalize

@Deprecated(since="9",
            forRemoval=true)
protected void finalize()
Deprecated, for removal: This API element is subject to removal in a future version.
The finalize method has been deprecated and will be removed. It is implemented as a no-op. Subclasses that override finalize in order to perform cleanup should be modified to use alternative cleanup mechanisms and to remove the overriding finalize method. The recommended cleanup for compressor is to explicitly call end method when it is no longer in use. If the end is not invoked explicitly the resource of the compressor will be released when the instance becomes unreachable.

Closes the compressor when garbage is collected.

Overrides:
finalize in class Object
See Also:
WeakReference, PhantomReference