org.apache.tools.bzip2

Class CBZip2OutputStream

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 {@link #close() 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:

 400k + (9 * blocksize).
 

To get the memory required for decompression by {@link CBZip2InputStream CBZip2InputStream} use

 65k + (5 * 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 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 intCLEARMASK
This constant is accessible by subclasses for historical purposes.
protected static intDEPTH_THRESH
This constant is accessible by subclasses for historical purposes.
protected static intGREATER_ICOST
This constant is accessible by subclasses for historical purposes.
protected static intLESSER_ICOST
This constant is accessible by subclasses for historical purposes.
static intMAX_BLOCKSIZE
The maximum supported blocksize == 9.
static intMIN_BLOCKSIZE
The minimum supported blocksize == 1.
protected static intQSORT_STACK_SIZE
This constant is accessible by subclasses for historical purposes.
protected static intSETMASK
This constant is accessible by subclasses for historical purposes.
protected static intSMALL_THRESH
This constant is accessible by subclasses for historical purposes.
protected static intWORK_FACTOR
This constant is accessible by subclasses for historical purposes.
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 intchooseBlockSize(long inputLength)
Chooses a blocksize based on the given length of the data to compress.
voidclose()
protected voidfinalize()
Overriden to close the stream.
voidflush()
intgetBlockSize()
Returns the blocksize parameter specified at construction time.
protected static voidhbMakeCodeLengths(char[] len, int[] freq, int alphaSize, int maxLen)
This method is accessible by subclasses for historical purposes.
voidwrite(int b)
voidwrite(byte[] buf, int offs, int len)

Field Detail

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.

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.

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.

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.

MAX_BLOCKSIZE

public static final int MAX_BLOCKSIZE
The maximum supported blocksize == 9.

MIN_BLOCKSIZE

public static final int MIN_BLOCKSIZE
The minimum supported blocksize == 1.

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.

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.

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.

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.

Constructor Detail

CBZip2OutputStream

public CBZip2OutputStream(OutputStream out)
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)
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

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 {@link #MIN_BLOCKSIZE} and {@link #MAX_BLOCKSIZE} both inclusive. For a negative inputLength this method returns MAX_BLOCKSIZE always.

close

public void close()

finalize

protected void finalize()
Overriden to close the stream.

flush

public void flush()

getBlockSize

public final int getBlockSize()
Returns the blocksize parameter specified at construction time.

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.

write

public void write(int b)

write

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