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Java Standard Edition (SE)

Deflater


compact1, compact2, compact3
java.util.zip

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.

    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.
    • 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.
    • Method Summary

      All Methods Instance Methods Concrete 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 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
      • 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.

        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 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.


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