org.apache.tools.bzip2

Class CBZip2OutputStream

java.lang.Object

java.io.OutputStream

org.apache.tools.bzip2.CBZip2OutputStream

All Implemented Interfaces:

java.io.Closeable, java.io.Flushable, java.lang.AutoCloseable, BZip2Constants

public class CBZip2OutputStream
extends java.io.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

Fields

Modifier and Type	Field and Description
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.tools.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

Constructors

Constructor and Description
CBZip2OutputStream(java.io.OutputStream out) Constructs a new CBZip2OutputStream with a blocksize of 900k.
CBZip2OutputStream(java.io.OutputStream out, int blockSize) Constructs a new CBZip2OutputStream with specified blocksize.

Method Summary

Methods

Modifier and Type	Method and Description
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(java.io.OutputStream out)
                   throws java.io.IOException

Constructs a new CBZip2OutputStream with a blocksize of 900k.

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

Parameters:

out - * the destination stream.

Throws:

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

java.lang.NullPointerException - if out == null.

CBZip2OutputStream

public CBZip2OutputStream(java.io.OutputStream out,
                  int blockSize)
                   throws java.io.IOException

Constructs a new CBZip2OutputStream with specified blocksize.

Attention: The caller is responsible 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:

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

java.lang.IllegalArgumentException - if (blockSize < 1) || (blockSize > 9).

java.lang.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 java.io.IOException

Specified by:

write in class java.io.OutputStream

Throws:

java.io.IOException

finalize

protected void finalize()
                 throws java.lang.Throwable

Overriden to close the stream.

Overrides:

finalize in class java.lang.Object

Throws:

java.lang.Throwable

finish

public void finish()
            throws java.io.IOException

Throws:

java.io.IOException

close

public void close()
           throws java.io.IOException

Specified by:

close in interface java.io.Closeable

Specified by:

close in interface java.lang.AutoCloseable

Overrides:

close in class java.io.OutputStream

Throws:

java.io.IOException

flush

public void flush()
           throws java.io.IOException

Specified by:

flush in interface java.io.Flushable

Overrides:

flush in class java.io.OutputStream

Throws:

java.io.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 java.io.IOException

Overrides:

write in class java.io.OutputStream

Throws:

java.io.IOException