org.apache.commons.compress.compressors.bzip2
Class BZip2CompressorOutputStream

java.lang.Object
  java.io.OutputStream
      org.apache.commons.compress.compressors.CompressorOutputStream
          org.apache.commons.compress.compressors.bzip2.BZip2CompressorOutputStream

All Implemented Interfaces:

Closeable, Flushable

public class BZip2CompressorOutputStream
extends CompressorOutputStream

An output stream that compresses into the BZip2 format into another stream.

The compression requires large amounts of memory. Thus you should call the close() method as soon as possible, to force BZip2CompressorOutputStream 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 BZip2CompressorInputStream 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 BZip2CompressorInputStream 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

static int	BASEBLOCKSIZE
static int	G_SIZE
static int	MAX_ALPHA_SIZE
static int	MAX_BLOCKSIZE The maximum supported blocksize == 9.
static int	MAX_CODE_LEN
static int	MAX_SELECTORS
static int	MIN_BLOCKSIZE The minimum supported blocksize == 1.
static int	N_GROUPS
static int	N_ITERS
static int	NUM_OVERSHOOT_BYTES
static int	RUNA
static int	RUNB

Constructor Summary

BZip2CompressorOutputStream(OutputStream out)
Constructs a new CBZip2OutputStream with a blocksize of 900k.

BZip2CompressorOutputStream(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.
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

BASEBLOCKSIZE

public static final int BASEBLOCKSIZE

See Also:

Constant Field Values

MAX_ALPHA_SIZE

public static final int MAX_ALPHA_SIZE

See Also:

Constant Field Values

MAX_CODE_LEN

public static final int MAX_CODE_LEN

See Also:

Constant Field Values

RUNA

public static final int RUNA

See Also:

Constant Field Values

RUNB

public static final int RUNB

See Also:

Constant Field Values

N_GROUPS

public static final int N_GROUPS

See Also:

Constant Field Values

G_SIZE

public static final int G_SIZE

See Also:

Constant Field Values

N_ITERS

public static final int N_ITERS

See Also:

Constant Field Values

MAX_SELECTORS

public static final int MAX_SELECTORS

See Also:

Constant Field Values

NUM_OVERSHOOT_BYTES

public static final int NUM_OVERSHOOT_BYTES

See Also:

Constant Field Values

Constructor Detail

BZip2CompressorOutputStream

public BZip2CompressorOutputStream(OutputStream out)
                            throws IOException

Constructs a new CBZip2OutputStream with a blocksize of 900k.

Parameters:

out - the destination stream.

Throws:

IOException - if an I/O error occurs in the specified stream.

NullPointerException - if out == null.

BZip2CompressorOutputStream

public BZip2CompressorOutputStream(OutputStream out,
                                   int blockSize)
                            throws IOException

Constructs a new CBZip2OutputStream with specified blocksize.

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

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