Class CBZip2OutputStream
- All Implemented Interfaces:
Closeable
,Flushable
,AutoCloseable
,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>.
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
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Field Summary
Modifier and TypeFieldDescriptionprotected static final int
This constant is accessible by subclasses for historical purposes.protected static final int
This constant is accessible by subclasses for historical purposes.protected static final int
This constant is accessible by subclasses for historical purposes.protected static final int
This constant is accessible by subclasses for historical purposes.static final int
The maximum supported blocksize== 9
.static final int
The minimum supported blocksize== 1
.protected static final int
This constant is accessible by subclasses for historical purposes.protected static final int
This constant is accessible by subclasses for historical purposes.protected static final int
This constant is accessible by subclasses for historical purposes.protected static final int
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
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Constructor Summary
ConstructorDescriptionConstructs a newCBZip2OutputStream
with a blocksize of 900k.CBZip2OutputStream
(OutputStream out, int blockSize) Constructs a newCBZip2OutputStream
with specified blocksize. -
Method Summary
Modifier and TypeMethodDescriptionstatic int
chooseBlockSize
(long inputLength) Chooses a blocksize based on the given length of the data to compress.void
close()
protected void
finalize()
Overridden to close the stream.void
finish()
void
flush()
final int
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
nullOutputStream, write
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Field Details
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MIN_BLOCKSIZE
public static final int MIN_BLOCKSIZEThe minimum supported blocksize== 1
.- See Also:
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MAX_BLOCKSIZE
public static final int MAX_BLOCKSIZEThe maximum supported blocksize== 9
.- See Also:
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SETMASK
protected static final int SETMASKThis constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.- See Also:
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CLEARMASK
protected static final int CLEARMASKThis constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.- See Also:
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GREATER_ICOST
protected static final int GREATER_ICOSTThis constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.- See Also:
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LESSER_ICOST
protected static final int LESSER_ICOSTThis constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.- See Also:
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SMALL_THRESH
protected static final int SMALL_THRESHThis constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.- See Also:
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DEPTH_THRESH
protected static final int DEPTH_THRESHThis constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.- See Also:
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WORK_FACTOR
protected static final int WORK_FACTORThis constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.- See Also:
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QSORT_STACK_SIZE
protected static final int QSORT_STACK_SIZEThis 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:
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Constructor Details
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CBZip2OutputStream
Constructs a newCBZip2OutputStream
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:
IOException
- if an I/O error occurs in the specified stream.NullPointerException
- ifout == null
.
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CBZip2OutputStream
Constructs a newCBZip2OutputStream
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:
IOException
- if an I/O error occurs in the specified stream.IllegalArgumentException
- if(blockSize < 1) || (blockSize > 9)
.NullPointerException
- ifout == null
.- See Also:
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Method Details
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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.- Parameters:
len
- char[]freq
- char[]alphaSize
- intmaxLen
- int
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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 byCBZip2OutputStream
.- Returns:
- The blocksize, between
MIN_BLOCKSIZE
andMAX_BLOCKSIZE
both inclusive. For a negativeinputLength
this method returnsMAX_BLOCKSIZE
always.
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write
- Specified by:
write
in classOutputStream
- Throws:
IOException
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finalize
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finish
- Throws:
IOException
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close
- Specified by:
close
in interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
- Overrides:
close
in classOutputStream
- Throws:
IOException
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flush
- Specified by:
flush
in interfaceFlushable
- Overrides:
flush
in classOutputStream
- Throws:
IOException
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getBlockSize
public final int getBlockSize()Returns the blocksize parameter specified at construction time.- Returns:
- int
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write
- Overrides:
write
in classOutputStream
- Throws:
IOException
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