Package org.apache.poi.util

Class LZWDecompresser

  • Direct Known Subclasses:
    CompressedRTF, HDGFLZW
    public abstract class LZWDecompresser
extends java.lang.Object
    This class provides common functionality for the various LZW implementations in the different file formats. It's currently used by HDGF and HMEF.

    Two good resources on LZW are: http://en.wikipedia.org/wiki/LZW http://marknelson.us/1989/10/01/lzw-data-compression/

    • Field Summary

      Fields 
      Modifier and Type Field Description
      static int DICT_MASK
      the mask for calculating / wrapping dictionary offsets
      static int DICT_SIZE
      the size of our dictionary

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      byte[] decompress​(java.io.InputStream src)
      Decompresses the given input stream, returning the array of bytes of the decompressed input.
      void decompress​(java.io.InputStream src, java.io.OutputStream res)
      Perform a streaming decompression of the input.
      static int getMaxRecordLength()  
      static void setMaxRecordLength​(int length)  

      • Methods inherited from class java.lang.Object

        equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Field Detail

      • DICT_SIZE

        public static final int DICT_SIZE
        the size of our dictionary
        See Also:
        Constant Field Values

      • DICT_MASK

        public static final int DICT_MASK
        the mask for calculating / wrapping dictionary offsets
        See Also:
        Constant Field Values

    • Method Detail

      • setMaxRecordLength

        public static void setMaxRecordLength​(int length)
        Parameters:
        length - the max record length allowed for LZWDecompresser

      • getMaxRecordLength

        public static int getMaxRecordLength()
        Returns:
        the max record length allowed for LZWDecompresser

      • decompress

        public byte[] decompress​(java.io.InputStream src)
                  throws java.io.IOException
        Decompresses the given input stream, returning the array of bytes of the decompressed input.
        Throws:
        java.io.IOException

      • decompress

        public void decompress​(java.io.InputStream src,
                       java.io.OutputStream res)
                throws java.io.IOException
        Perform a streaming decompression of the input. Works by: 1) Reading a flag byte, the 8 bits of which tell you if the following 8 codes are compressed our un-compressed 2) Consider the 8 bits in turn 3) If the bit is set, the next code is un-compressed, so add it to the dictionary and output it 4) If the bit isn't set, then read in the length and start position in the dictionary, and output the bytes there 5) Loop until we've done all 8 bits, then read in the next flag byte
        Throws:
        java.io.IOException