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

java.lang.Object
  extended by java.io.OutputStream
      extended by 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
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