public class

Deflater

extends Object
java.lang.Object
   ↳ java.util.zip.Deflater

Class Overview

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. 

 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);

     // 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
 }

See Also

Summary

Constants
int BEST_COMPRESSION Compression level for best compression.
int BEST_SPEED Compression level for fastest compression.
int DEFAULT_COMPRESSION Default compression level.
int DEFAULT_STRATEGY Default compression strategy.
int DEFLATED Compression method for the deflate algorithm (the only one currently supported).
int FILTERED Compression strategy best used for data consisting mostly of small values with a somewhat random distribution.
int HUFFMAN_ONLY Compression strategy for Huffman coding only.
int NO_COMPRESSION Compression level for no compression.
Public Constructors
Deflater(int level, boolean nowrap)
Creates a new compressor using the specified compression level.
Deflater(int level)
Creates a new compressor using the specified compression level.
Deflater()
Creates a new compressor with the default compression level.
Public Methods
int deflate(byte[] b, int off, int len)
Fills specified buffer with compressed data.
int deflate(byte[] b)
Fills specified buffer with compressed data.
void end()
Closes the compressor and discards any unprocessed input.
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, int off, int len)
Sets preset dictionary for compression.
void setDictionary(byte[] b)
Sets preset dictionary for compression.
void setInput(byte[] b, int off, int len)
Sets input data for compression.
void setInput(byte[] b)
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.
Protected Methods
void finalize()
Closes the compressor when garbage is collected.
[Expand]
Inherited Methods
From class java.lang.Object

Constants

public static final int BEST_COMPRESSION

Compression level for best compression.

Constant Value: 9 (0x00000009)

public static final int BEST_SPEED

Compression level for fastest compression.

Constant Value: 1 (0x00000001)

public static final int DEFAULT_COMPRESSION

Default compression level.

Constant Value: -1 (0xffffffff)

public static final int DEFAULT_STRATEGY

Default compression strategy.

Constant Value: 0 (0x00000000)

public static final int DEFLATED

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

Constant Value: 8 (0x00000008)

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.

Constant Value: 1 (0x00000001)

public static final int HUFFMAN_ONLY

Compression strategy for Huffman coding only.

Constant Value: 2 (0x00000002)

public static final int NO_COMPRESSION

Compression level for no compression.

Constant Value: 0 (0x00000000)

Public Constructors

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

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)

public Deflater ()

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

Public Methods

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

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

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.

public void finish ()

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

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

public int getAdler ()

Returns the ADLER-32 value of the uncompressed data.

Returns
  • the ADLER-32 value of the uncompressed data

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

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

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

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

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

public void reset ()

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

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

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

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

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

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

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

Protected Methods

protected void finalize ()

Closes the compressor when garbage is collected.