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.

 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
 }

See Also:: Inflater

Field Summary

Fields
Modifier and Type	Field and 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.

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Constructor Summary

Constructors
Constructor and 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.

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Method Summary

Methods
Modifier and Type	Method and Description
`int`	`deflate(byte[] b)` Compresses the input data and fills specified buffer with compressed data.
`int`	`deflate(byte[] b, int off, int len)` Compresses the input data and fills specified buffer with compressed data.
`int`	`deflate(byte[] b, int off, int len, 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()` 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.

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Methods inherited from 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[] 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)
```
    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:
    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 written to the output buffer
  - deflate
```
public int deflate(byte[] b)
```
    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:
    b - the buffer for the compressed data
    
    Returns:
    the actual number of bytes of compressed data written to the output buffer
  - deflate
```
public int deflate(byte[] b,
          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.
    Parameters:
    b - 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
  - 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, 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

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Dokument erstellt 11/06/2005, zuletzt geändert 04/03/2020
Quelle des gedruckten Dokuments:https://www.gaudry.be/de/java-api-rf-java/util/zip/deflater.html

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Referenzen

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Inhaltsverzeichnis Haut

Class Deflater

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

DEFLATED

NO_COMPRESSION

BEST_SPEED

BEST_COMPRESSION

DEFAULT_COMPRESSION

FILTERED

HUFFMAN_ONLY

DEFAULT_STRATEGY

NO_FLUSH

SYNC_FLUSH

FULL_FLUSH

Constructor Detail

Deflater

Deflater

Deflater

Method Detail

setInput

setInput

setDictionary

setDictionary

setStrategy

setLevel

needsInput

finish

finished

deflate

deflate

deflate

getAdler

getTotalIn

getBytesRead

getTotalOut

getBytesWritten

reset

end

finalize

Referenzen