Class CBZip2OutputStream

  • All Implemented Interfaces:
    java.io.Closeable, java.io.Flushable, java.lang.AutoCloseable, BZip2Constants

    public class CBZip2OutputStream
    extends java.io.OutputStream
    implements BZip2Constants
    An output stream that compresses into the BZip2 format (without the file header chars) into another stream.

    The compression requires large amounts of memory. Thus you should call the close() method as soon as possible, to force CBZip2OutputStream to release the allocated memory.

    You can shrink the amount of allocated memory and maybe raise the compression speed by choosing a lower blocksize, which in turn may cause a lower compression ratio. You can avoid unnecessary memory allocation by avoiding using a blocksize which is bigger than the size of the input.

    You can compute the memory usage for compressing by the following formula:

     <code>400k + (9 * blocksize)</code>.
     

    To get the memory required for decompression by CBZip2InputStream use

     <code>65k + (5 * blocksize)</code>.
     
    Memory usage by blocksize
    Blocksize Compression
    memory usage
    Decompression
    memory usage
    100k 1300k 565k
    200k 2200k 1065k
    300k 3100k 1565k
    400k 4000k 2065k
    500k 4900k 2565k
    600k 5800k 3065k
    700k 6700k 3565k
    800k 7600k 4065k
    900k 8500k 4565k

    For decompression CBZip2InputStream allocates less memory if the bzipped input is smaller than one block.

    Instances of this class are not threadsafe.

    TODO: Update to BZip2 1.0.1

    • Constructor Summary

      Constructors 
      Constructor Description
      CBZip2OutputStream​(java.io.OutputStream out)
      Constructs a new CBZip2OutputStream with a blocksize of 900k.
      CBZip2OutputStream​(java.io.OutputStream out, int blockSize)
      Constructs a new CBZip2OutputStream with specified blocksize.
    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      static int chooseBlockSize​(long inputLength)
      Chooses a blocksize based on the given length of the data to compress.
      void close()  
      protected void finalize()
      Overridden to close the stream.
      void finish()  
      void flush()  
      int getBlockSize()
      Returns the blocksize parameter specified at construction time.
      protected static void hbMakeCodeLengths​(char[] len, int[] freq, int alphaSize, int maxLen)
      This method is accessible by subclasses for historical purposes.
      void write​(byte[] buf, int offs, int len)  
      void write​(int b)
      • Methods inherited from class java.io.OutputStream

        nullOutputStream, write
      • Methods inherited from class java.lang.Object

        clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    • Field Detail

      • MIN_BLOCKSIZE

        public static final int MIN_BLOCKSIZE
        The minimum supported blocksize == 1.
        See Also:
        Constant Field Values
      • MAX_BLOCKSIZE

        public static final int MAX_BLOCKSIZE
        The maximum supported blocksize == 9.
        See Also:
        Constant Field Values
      • SETMASK

        protected static final int SETMASK
        This constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.
        See Also:
        Constant Field Values
      • CLEARMASK

        protected static final int CLEARMASK
        This constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.
        See Also:
        Constant Field Values
      • GREATER_ICOST

        protected static final int GREATER_ICOST
        This constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.
        See Also:
        Constant Field Values
      • LESSER_ICOST

        protected static final int LESSER_ICOST
        This constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.
        See Also:
        Constant Field Values
      • SMALL_THRESH

        protected static final int SMALL_THRESH
        This constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.
        See Also:
        Constant Field Values
      • DEPTH_THRESH

        protected static final int DEPTH_THRESH
        This constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.
        See Also:
        Constant Field Values
      • WORK_FACTOR

        protected static final int WORK_FACTOR
        This constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.
        See Also:
        Constant Field Values
      • QSORT_STACK_SIZE

        protected static final int QSORT_STACK_SIZE
        This constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.

        If you are ever unlucky/improbable enough to get a stack overflow whilst sorting, increase the following constant and try again. In practice I have never seen the stack go above 27 elems, so the following limit seems very generous.

        See Also:
        Constant Field Values
    • Constructor Detail

      • CBZip2OutputStream

        public CBZip2OutputStream​(java.io.OutputStream out)
                           throws java.io.IOException
        Constructs a new CBZip2OutputStream with a blocksize of 900k.

        Attention: The caller is responsible to write the two BZip2 magic bytes "BZ" to the specified stream prior to calling this constructor.

        Parameters:
        out - * the destination stream.
        Throws:
        java.io.IOException - if an I/O error occurs in the specified stream.
        java.lang.NullPointerException - if out == null.
      • CBZip2OutputStream

        public CBZip2OutputStream​(java.io.OutputStream out,
                                  int blockSize)
                           throws java.io.IOException
        Constructs a new CBZip2OutputStream with specified blocksize.

        Attention: The caller is responsible to write the two BZip2 magic bytes "BZ" to the specified stream prior to calling this constructor.

        Parameters:
        out - the destination stream.
        blockSize - the blockSize as 100k units.
        Throws:
        java.io.IOException - if an I/O error occurs in the specified stream.
        java.lang.IllegalArgumentException - if (blockSize < 1) || (blockSize > 9).
        java.lang.NullPointerException - if out == null.
        See Also:
        MIN_BLOCKSIZE, MAX_BLOCKSIZE
    • Method Detail

      • hbMakeCodeLengths

        protected static void hbMakeCodeLengths​(char[] len,
                                                int[] freq,
                                                int alphaSize,
                                                int maxLen)
        This method is accessible by subclasses for historical purposes. If you don't know what it does then you don't need it.
        Parameters:
        len - char[]
        freq - char[]
        alphaSize - int
        maxLen - int
      • chooseBlockSize

        public static int chooseBlockSize​(long inputLength)
        Chooses a blocksize based on the given length of the data to compress.
        Parameters:
        inputLength - The length of the data which will be compressed by CBZip2OutputStream.
        Returns:
        The blocksize, between MIN_BLOCKSIZE and MAX_BLOCKSIZE both inclusive. For a negative inputLength this method returns MAX_BLOCKSIZE always.
      • write

        public void write​(int b)
                   throws java.io.IOException
        Specified by:
        write in class java.io.OutputStream
        Throws:
        java.io.IOException
      • finalize

        protected void finalize()
                         throws java.lang.Throwable
        Overridden to close the stream.
        Overrides:
        finalize in class java.lang.Object
        Throws:
        java.lang.Throwable
      • finish

        public void finish()
                    throws java.io.IOException
        Throws:
        java.io.IOException
      • close

        public void close()
                   throws java.io.IOException
        Specified by:
        close in interface java.lang.AutoCloseable
        Specified by:
        close in interface java.io.Closeable
        Overrides:
        close in class java.io.OutputStream
        Throws:
        java.io.IOException
      • flush

        public void flush()
                   throws java.io.IOException
        Specified by:
        flush in interface java.io.Flushable
        Overrides:
        flush in class java.io.OutputStream
        Throws:
        java.io.IOException
      • getBlockSize

        public final int getBlockSize()
        Returns the blocksize parameter specified at construction time.
        Returns:
        int
      • write

        public void write​(byte[] buf,
                          int offs,
                          int len)
                   throws java.io.IOException
        Overrides:
        write in class java.io.OutputStream
        Throws:
        java.io.IOException