Package 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, AutoCloseable, BZip2Constants

public class BZip2CompressorOutputStream
extends CompressorOutputStream
implements BZip2Constants

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

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
(package private) static final class	BZip2CompressorOutputStream.Data

Field Summary

Fields

Modifier and Type	Field	Description
private final int	allowableBlockSize
private int	blockCRC
private final int	blockSize100k	Always: in the range 0 ..
private BlockSort	blockSorter
private int	bsBuff
private int	bsLive
private boolean	closed
private int	combinedCRC
private final CRC	crc
private int	currentChar
private BZip2CompressorOutputStream.Data	data	All memory intensive stuff.
private static final int	GREATER_ICOST
private int	last	Index of the last char in the block, so the block size == last + 1.
private static final int	LESSER_ICOST
static final int	MAX_BLOCKSIZE	The maximum supported blocksize == 9.
static final int	MIN_BLOCKSIZE	The minimum supported blocksize == 1.
private int	nInUse
private int	nMTF
private OutputStream	out
private int	runLength

Fields inherited from interface org.apache.commons.compress.compressors.bzip2.BZip2Constants

BASEBLOCKSIZE, G_SIZE, MAX_ALPHA_SIZE, MAX_CODE_LEN, MAX_SELECTORS, N_GROUPS, N_ITERS, NUM_OVERSHOOT_BYTES, RUNA, RUNB

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
private void	blockSort()
private void	bsFinishedWithStream()
private void	bsPutInt(int u)
private void	bsPutUByte(int c)
private void	bsW(int n, int v)
static int	chooseBlockSize(long inputLength)	Chooses a blocksize based on the given length of the data to compress.
void	close()
private void	endBlock()
private void	endCompression()
void	finish()
void	flush()
private void	generateMTFValues()
final int	getBlockSize()	Returns the blocksize parameter specified at construction time.
private static void	hbAssignCodes(int[] code, byte[] length, int minLen, int maxLen, int alphaSize)
private static void	hbMakeCodeLengths(byte[] len, int[] freq, BZip2CompressorOutputStream.Data dat, int alphaSize, int maxLen)
private void	init()	Writes magic bytes like BZ on the first position of the stream and bytes indicating the file-format, which is huffmanized, followed by a digit indicating blockSize100k.
private void	initBlock()
private void	moveToFrontCodeAndSend()
private void	sendMTFValues()
private void	sendMTFValues0(int nGroups, int alphaSize)
private int	sendMTFValues1(int nGroups, int alphaSize)
private void	sendMTFValues2(int nGroups, int nSelectors)
private void	sendMTFValues3(int nGroups, int alphaSize)
private void	sendMTFValues4()
private void	sendMTFValues5(int nGroups, int nSelectors)
private void	sendMTFValues6(int nGroups, int alphaSize)
private void	sendMTFValues7()
void	write(byte[] buf, int offs, int len)
void	write(int b)
private void	write0(int b)	Keeps track of the last bytes written and implicitly performs run-length encoding as the first step of the bzip2 algorithm.
private void	writeRun()	Writes the current byte to the buffer, run-length encoding it if it has been repeated at least four times (the first step RLEs sequences of four identical bytes).

Methods inherited from class java.io.OutputStream

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

GREATER_ICOST

private static final int GREATER_ICOST

See Also:

• Constant Field Values

LESSER_ICOST

private static final int LESSER_ICOST

See Also:

• Constant Field Values

last

private int last

Index of the last char in the block, so the block size == last + 1.

blockSize100k

private final int blockSize100k

Always: in the range 0 .. 9. The current block size is 100000 * this number.

bsBuff

private int bsBuff

bsLive

private int bsLive

crc

private final CRC crc

nInUse

private int nInUse

nMTF

private int nMTF

currentChar

private int currentChar

runLength

private int runLength

blockCRC

private int blockCRC

combinedCRC

private int combinedCRC

allowableBlockSize

private final int allowableBlockSize

data

private BZip2CompressorOutputStream.Data data

All memory intensive stuff.

blockSorter

private BlockSort blockSorter

out

private OutputStream out

closed

private volatile boolean closed

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.

hbAssignCodes

private static void hbAssignCodes(int[] code,
 byte[] length,
 int minLen,
 int maxLen,
 int alphaSize)

hbMakeCodeLengths

private static void hbMakeCodeLengths(byte[] len,
 int[] freq,
 BZip2CompressorOutputStream.Data dat,
 int alphaSize,
 int maxLen)

blockSort

private void blockSort()

bsFinishedWithStream

private void bsFinishedWithStream()
                           throws IOException

Throws:

IOException

bsPutInt

private void bsPutInt(int u)
               throws IOException

Throws:

IOException

bsPutUByte

private void bsPutUByte(int c)
                 throws IOException

Throws:

IOException

bsW

private void bsW(int n,
 int v)
          throws IOException

Throws:

IOException

close

public void close()
           throws IOException

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Overrides:

close in class OutputStream

Throws:

IOException

endBlock

private void endBlock()
               throws IOException

Throws:

IOException

endCompression

private void endCompression()
                     throws IOException

Throws:

IOException

finish

public void finish()
            throws IOException

Throws:

IOException

flush

public void flush()
           throws IOException

Specified by:

flush in interface Flushable

Overrides:

flush in class OutputStream

Throws:

IOException

generateMTFValues

private void generateMTFValues()

getBlockSize

public final int getBlockSize()

Returns the blocksize parameter specified at construction time.

Returns:

the blocksize parameter specified at construction time

init

private void init()
           throws IOException

Writes magic bytes like BZ on the first position of the stream and bytes indicating the file-format, which is huffmanized, followed by a digit indicating blockSize100k.

Throws:

IOException - if the magic bytes could not been written

initBlock

private void initBlock()

moveToFrontCodeAndSend

private void moveToFrontCodeAndSend()
                             throws IOException

Throws:

IOException

sendMTFValues

private void sendMTFValues()
                    throws IOException

Throws:

IOException

sendMTFValues0

private void sendMTFValues0(int nGroups,
 int alphaSize)

sendMTFValues1

private int sendMTFValues1(int nGroups,
 int alphaSize)

sendMTFValues2

private void sendMTFValues2(int nGroups,
 int nSelectors)

sendMTFValues3

private void sendMTFValues3(int nGroups,
 int alphaSize)

sendMTFValues4

private void sendMTFValues4()
                     throws IOException

Throws:

IOException

sendMTFValues5

private void sendMTFValues5(int nGroups,
 int nSelectors)
                     throws IOException

Throws:

IOException

sendMTFValues6

private void sendMTFValues6(int nGroups,
 int alphaSize)
                     throws IOException

Throws:

IOException

sendMTFValues7

private void sendMTFValues7()
                     throws IOException

Throws:

IOException

write

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

Overrides:

write in class OutputStream

Throws:

IOException

write

public void write(int b)
           throws IOException

Specified by:

write in class OutputStream

Throws:

IOException

write0

private void write0(int b)
             throws IOException

Keeps track of the last bytes written and implicitly performs run-length encoding as the first step of the bzip2 algorithm.

Throws:

IOException

writeRun

private void writeRun()
               throws IOException

Writes the current byte to the buffer, run-length encoding it if it has been repeated at least four times (the first step RLEs sequences of four identical bytes).

Flushes the current block before writing data if it is full.

"write to the buffer" means adding to data.buffer starting two steps "after" this.last - initially starting at index 1 (not 0) - and updating this.last to point to the last index written minus 1.

Throws:

IOException