## org.apache.hadoop.io.compress.bzip2
Class CBZip2OutputStream

    java.lang.Object
      java.io.OutputStream
          org.apache.hadoop.io.compress.bzip2.CBZip2OutputStream

All Implemented Interfaces:
  Closeable, Flushable, BZip2Constants

    public class CBZip2OutputStream

extends 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

Field Summary
`protected static int` `CLEARMASK` This constant is accessible by subclasses for historical purposes.
`protected static int` `DEPTH_THRESH` This constant is accessible by subclasses for historical purposes.
`protected static int` `GREATER_ICOST` This constant is accessible by subclasses for historical purposes.
`protected static int` `LESSER_ICOST` This constant is accessible by subclasses for historical purposes.
`static int` `MAX_BLOCKSIZE` The maximum supported blocksize `== 9`.
`static int` `MIN_BLOCKSIZE` The minimum supported blocksize `== 1`.
`protected static int` `QSORT_STACK_SIZE` This constant is accessible by subclasses for historical purposes.
`protected static int` `SETMASK` This constant is accessible by subclasses for historical purposes.
`protected static int` `SMALL_THRESH` This constant is accessible by subclasses for historical purposes.
`protected static int` `WORK_FACTOR` This constant is accessible by subclasses for historical purposes.

Fields inherited from interface org.apache.hadoop.io.compress.bzip2.BZip2Constants
`baseBlockSize, G_SIZE, MAX_ALPHA_SIZE, MAX_CODE_LEN, MAX_SELECTORS, N_GROUPS, N_ITERS, NUM_OVERSHOOT_BYTES, rNums, RUNA, RUNB`

Constructor Summary
`CBZip2OutputStream(OutputStream out)` Constructs a new `CBZip2OutputStream` with a blocksize of 900k.
`CBZip2OutputStream(OutputStream out, int blockSize)` Constructs a new `CBZip2OutputStream` with specified blocksize.

Method Summary
`static int` `chooseBlockSize(long inputLength)` Chooses a blocksize based on the given length of the data to compress.
`void` `close()`
`protected void` `finalize()` Overriden 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
`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(OutputStream out)
                       throws IOException

  Constructs a new `CBZip2OutputStream` with a blocksize of 900k.

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

  Parameters:
    `out` - * the destination stream.
  Throws:
    `IOException` - if an I/O error occurs in the specified stream.
    `NullPointerException` - if `out == null`.

### CBZip2OutputStream

    public CBZip2OutputStream(OutputStream out,
                              int blockSize)
                       throws IOException

  Constructs a new `CBZip2OutputStream` with specified blocksize.

  Attention: The caller is resonsible 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:
    `IOException` - if an I/O error occurs in the specified stream.
    `IllegalArgumentException` - if `(blockSize < 1) || (blockSize > 9)`.
    `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.

### 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 IOException

  Specified by:
    `write` in class `OutputStream`
  Throws:
    `IOException`

### finalize

    protected void finalize()
                     throws Throwable

  Overriden to close the stream.

  Overrides:
    `finalize` in class `Object`
  Throws:
    `Throwable`

### finish

    public void finish()
                throws IOException

  Throws:
    `IOException`

### close

    public void close()
               throws IOException

  Specified by:
    `close` in interface `Closeable`
  Overrides:
    `close` in class `OutputStream`
  Throws:
    `IOException`

### flush

    public void flush()
               throws IOException

  Specified by:
    `flush` in interface `Flushable`
  Overrides:
    `flush` in class `OutputStream`
  Throws:
    `IOException`

### getBlockSize

    public final int getBlockSize()

  Returns the blocksize parameter specified at construction time.

### write

    public void write(byte[] buf,
                      int offs,
                      int len)
               throws IOException

  Overrides:
    `write` in class `OutputStream`
  Throws:
    `IOException`

Copyright © 2009 The Apache Software Foundation