Package org.apache.commons.compress.compressors.bzip2

Class BZip2CompressorOutputStream

java.lang.Object

java.io.OutputStream

java.io.FilterOutputStream

org.apache.commons.compress.CompressFilterOutputStream<OutputStream>

org.apache.commons.compress.compressors.CompressorOutputStream<OutputStream>

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

All Implemented Interfaces:

Closeable, Flushable, AutoCloseable

public class BZip2CompressorOutputStream
extends CompressorOutputStream<OutputStream>

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

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

This class is not thread-safe

Field Summary

Fields

Modifier and Type	Field	Description
static final int	BASEBLOCKSIZE	Constant 100000.
static final int	G_SIZE	Constant 50.
static final int	MAX_ALPHA_SIZE	Constant 258.
static final int	MAX_BLOCKSIZE	The maximum supported blocksize == 9.
static final int	MAX_CODE_LEN	Constant 23.
static final int	MAX_SELECTORS	Constant 18002.
static final int	MIN_BLOCKSIZE	The minimum supported blocksize == 1.
static final int	N_GROUPS	Constant 6.
static final int	N_ITERS	Constant 4.
static final int	NUM_OVERSHOOT_BYTES	Constant 20.
static final int	RUNA	Constant 0.
static final int	RUNB	Constant 1.

Fields inherited from class java.io.FilterOutputStream

out

Constructor Summary

Constructors

Constructor	Description
BZip2CompressorOutputStream(OutputStream out)	Constructs a new BZip2CompressorOutputStream with a blocksize of 900k.
BZip2CompressorOutputStream(OutputStream out, int blockSize)	Constructs a new BZip2CompressorOutputStream with specified blocksize.

Method Summary

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()
void	finish()	Finishes the addition of entries to this stream, without closing it.
void	flush()
final 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 org.apache.commons.compress.CompressFilterOutputStream

checkOpen, isClosed, isFinished, out, write, write, writeUsAscii, writeUsAsciiRaw, writeUtf8

Methods inherited from class java.io.FilterOutputStream

write

Methods inherited from class java.lang.Object

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

Field Details

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

static final int BASEBLOCKSIZE

Constant 100000.

See Also:

• Constant Field Values

MAX_ALPHA_SIZE

static final int MAX_ALPHA_SIZE

Constant 258.

See Also:

• Constant Field Values

MAX_CODE_LEN

static final int MAX_CODE_LEN

Constant 23.

See Also:

• Constant Field Values

RUNA

static final int RUNA

Constant 0.

See Also:

• Constant Field Values

RUNB

static final int RUNB

Constant 1.

See Also:

• Constant Field Values

N_GROUPS

static final int N_GROUPS

Constant 6.

See Also:

• Constant Field Values

G_SIZE

static final int G_SIZE

Constant 50.

See Also:

• Constant Field Values

N_ITERS

static final int N_ITERS

Constant 4.

See Also:

• Constant Field Values

MAX_SELECTORS

static final int MAX_SELECTORS

Constant 18002.

See Also:

• Constant Field Values

NUM_OVERSHOOT_BYTES

static final int NUM_OVERSHOOT_BYTES

Constant 20.

See Also:

• Constant Field Values

Constructor Details

BZip2CompressorOutputStream

public BZip2CompressorOutputStream(OutputStream out)
                            throws IOException

Constructs a new BZip2CompressorOutputStream 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 BZip2CompressorOutputStream 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 Details

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 BZip2CompressorOutputStream.

Returns:

The blocksize, between MIN_BLOCKSIZE and MAX_BLOCKSIZE both inclusive. For a negative inputLength this method returns MAX_BLOCKSIZE always.

close

public void close()
           throws IOException

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Overrides:

close in class CompressFilterOutputStream<OutputStream>

Throws:

IOException

finish

public void finish()
            throws IOException

Description copied from class: CompressFilterOutputStream

Finishes the addition of entries to this stream, without closing it. Additional data can be written, if the format supports it.

Overrides:

finish in class CompressFilterOutputStream<OutputStream>

Throws:

IOException - Maybe thrown by subclasses if the user forgets to close the entry.

flush

public void flush()
           throws IOException

Specified by:

flush in interface Flushable

Overrides:

flush in class FilterOutputStream

Throws:

IOException

getBlockSize

public final int getBlockSize()

Returns the blocksize parameter specified at construction time.

Returns:

the blocksize parameter specified at construction time

write

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

Overrides:

write in class FilterOutputStream

Throws:

IOException

write

public void write(int b)
           throws IOException

Overrides:

write in class FilterOutputStream

Throws:

IOException