java.util.zip

Class Inflater


  • public class Inflater
extends Object
    This class provides support for general purpose decompression 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:
    Deflater

    • Constructor Summary

      Constructors

      Constructor and Description
      Inflater()
      Creates a new decompressor.
      Inflater(boolean nowrap)
      Creates a new decompressor.

    • Method Summary

      Modifier and Type Method and Description
      void end()
      Closes the decompressor and discards any unprocessed input.
      protected void finalize()
      Closes the decompressor when garbage is collected.
      boolean finished()
      Returns true if the end of the compressed data stream has been reached.
      int getAdler()
      Returns the ADLER-32 value of the uncompressed data.
      long getBytesRead()
      Returns the total number of compressed bytes input so far.
      long getBytesWritten()
      Returns the total number of uncompressed bytes output so far.
      int getRemaining()
      Returns the total number of bytes remaining in the input buffer.
      int getTotalIn()
      Returns the total number of compressed bytes input so far.
      int getTotalOut()
      Returns the total number of uncompressed bytes output so far.
      int inflate(byte[] b)
      Uncompresses bytes into specified buffer.
      int inflate(byte[] b, int off, int len)
      Uncompresses bytes into specified buffer.
      boolean needsDictionary()
      Returns true if a preset dictionary is needed for decompression.
      boolean needsInput()
      Returns true if no data remains in the input buffer.
      void reset()
      Resets inflater so that a new set of input data can be processed.
      void setDictionary(byte[] b)
      Sets the preset dictionary to the given array of bytes.
      void setDictionary(byte[] b, int off, int len)
      Sets the preset dictionary to the given array of bytes.
      void setInput(byte[] b)
      Sets input data for decompression.
      void setInput(byte[] b, int off, int len)
      Sets input data for decompression.

    • Constructor Detail

      • Inflater

        public Inflater(boolean nowrap)
        Creates a new decompressor. If the parameter 'nowrap' is true then the ZLIB header and checksum fields will not be used. This provides compatibility with the compression format used by both GZIP and PKZIP.

        Note: When using the 'nowrap' option it is also necessary to provide an extra "dummy" byte as input. This is required by the ZLIB native library in order to support certain optimizations.

        Parameters:
        nowrap - if true then support GZIP compatible compression

      • Inflater

        public Inflater()
        Creates a new decompressor.

    • Method Detail

      • setInput

        public void setInput(byte[] b,
                     int off,
                     int len)
        Sets input data for decompression. 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 input data
        len - the length of the input data
        See Also:
        needsInput()

      • setInput

        public void setInput(byte[] b)
        Sets input data for decompression. 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 the preset dictionary to the given array of bytes. Should be called when inflate() returns 0 and needsDictionary() returns true indicating that a preset dictionary is required. The method getAdler() can be used to get the Adler-32 value of the dictionary needed.
        Parameters:
        b - the dictionary data bytes
        off - the start offset of the data
        len - the length of the data
        See Also:
        needsDictionary(), getAdler()

      • setDictionary

        public void setDictionary(byte[] b)
        Sets the preset dictionary to the given array of bytes. Should be called when inflate() returns 0 and needsDictionary() returns true indicating that a preset dictionary is required. The method getAdler() can be used to get the Adler-32 value of the dictionary needed.
        Parameters:
        b - the dictionary data bytes
        See Also:
        needsDictionary(), getAdler()

      • getRemaining

        public int getRemaining()
        Returns the total number of bytes remaining in the input buffer. This can be used to find out what bytes still remain in the input buffer after decompression has finished.
        Returns:
        the total number of bytes remaining in the input buffer

      • needsInput

        public boolean needsInput()
        Returns true if no data remains in the input buffer. This can be used to determine if #setInput should be called in order to provide more input.
        Returns:
        true if no data remains in the input buffer

      • needsDictionary

        public boolean needsDictionary()
        Returns true if a preset dictionary is needed for decompression.
        Returns:
        true if a preset dictionary is needed for decompression
        See Also:
        setDictionary(byte[], int, int)

      • finished

        public boolean finished()
        Returns true if the end of the compressed data stream has been reached.
        Returns:
        true if the end of the compressed data stream has been reached

      • inflate

        public int inflate(byte[] b,
                   int off,
                   int len)
            throws DataFormatException
        Uncompresses bytes into specified buffer. Returns actual number of bytes uncompressed. A return value of 0 indicates that needsInput() or needsDictionary() should be called in order to determine if more input data or a preset dictionary is required. In the latter case, getAdler() can be used to get the Adler-32 value of the dictionary required.
        Parameters:
        b - the buffer for the uncompressed data
        off - the start offset of the data
        len - the maximum number of uncompressed bytes
        Returns:
        the actual number of uncompressed bytes
        Throws:
        DataFormatException - if the compressed data format is invalid
        See Also:
        needsInput(), needsDictionary()

      • inflate

        public int inflate(byte[] b)
            throws DataFormatException
        Uncompresses bytes into specified buffer. Returns actual number of bytes uncompressed. A return value of 0 indicates that needsInput() or needsDictionary() should be called in order to determine if more input data or a preset dictionary is required. In the latter case, getAdler() can be used to get the Adler-32 value of the dictionary required.
        Parameters:
        b - the buffer for the uncompressed data
        Returns:
        the actual number of uncompressed bytes
        Throws:
        DataFormatException - if the compressed data format is invalid
        See Also:
        needsInput(), needsDictionary()

      • 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 compressed 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 compressed bytes input so far

      • getBytesRead

        public long getBytesRead()
        Returns the total number of compressed bytes input so far.
        Returns:
        the total (non-negative) number of compressed bytes input so far
        Since:
        1.5

      • getTotalOut

        public int getTotalOut()
        Returns the total number of uncompressed 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 uncompressed bytes output so far

      • getBytesWritten

        public long getBytesWritten()
        Returns the total number of uncompressed bytes output so far.
        Returns:
        the total (non-negative) number of uncompressed bytes output so far
        Since:
        1.5

      • reset

        public void reset()
        Resets inflater so that a new set of input data can be processed.

      • end

        public void end()
        Closes the decompressor and discards any unprocessed input. This method should be called when the decompressor is no longer being used, but will also be called automatically by the finalize() method. Once this method is called, the behavior of the Inflater object is undefined.