org.apache.tools.bzip2
public class CBZip2OutputStream extends OutputStream implements BZip2Constants
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 | |
---|---|
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. |
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 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(int b) |
void | write(byte[] buf, int offs, int len) |
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.
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
.
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
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.