Class CBZip2OutputStream
- All Implemented Interfaces:
java.io.Closeable,java.io.Flushable,java.lang.AutoCloseable,BZip2Constants
public class CBZip2OutputStream extends java.io.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>.
| 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
Fields Modifier and Type Field Description protected static intCLEARMASKThis constant is accessible by subclasses for historical purposes.protected static intDEPTH_THRESHThis constant is accessible by subclasses for historical purposes.protected static intGREATER_ICOSTThis constant is accessible by subclasses for historical purposes.protected static intLESSER_ICOSTThis constant is accessible by subclasses for historical purposes.static intMAX_BLOCKSIZEThe maximum supported blocksize== 9.static intMIN_BLOCKSIZEThe minimum supported blocksize== 1.protected static intQSORT_STACK_SIZEThis constant is accessible by subclasses for historical purposes.protected static intSETMASKThis constant is accessible by subclasses for historical purposes.protected static intSMALL_THRESHThis constant is accessible by subclasses for historical purposes.protected static intWORK_FACTORThis 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 Description CBZip2OutputStream(java.io.OutputStream out)Constructs a newCBZip2OutputStreamwith a blocksize of 900k.CBZip2OutputStream(java.io.OutputStream out, int blockSize)Constructs a newCBZip2OutputStreamwith specified blocksize. -
Method Summary
Modifier and Type Method Description static intchooseBlockSize(long inputLength)Chooses a blocksize based on the given length of the data to compress.voidclose()protected voidfinalize()Overridden to close the stream.voidfinish()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(byte[] buf, int offs, int len)voidwrite(int b)
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Field Details
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MIN_BLOCKSIZE
public static final int MIN_BLOCKSIZEThe minimum supported blocksize== 1.- See Also:
- Constant Field Values
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MAX_BLOCKSIZE
public static final int MAX_BLOCKSIZEThe maximum supported blocksize== 9.- See Also:
- Constant Field Values
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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:
- Constant Field Values
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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:
- Constant Field Values
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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:
- Constant Field Values
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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:
- Constant Field Values
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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:
- Constant Field Values
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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:
- Constant Field Values
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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:
- Constant Field Values
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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:
- Constant Field Values
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Constructor Details
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CBZip2OutputStream
public CBZip2OutputStream(java.io.OutputStream out) throws java.io.IOExceptionConstructs a newCBZip2OutputStreamwith 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- ifout == null.
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CBZip2OutputStream
public CBZip2OutputStream(java.io.OutputStream out, int blockSize) throws java.io.IOExceptionConstructs a newCBZip2OutputStreamwith 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- ifout == null.- See Also:
MIN_BLOCKSIZE,MAX_BLOCKSIZE
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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_BLOCKSIZEandMAX_BLOCKSIZEboth inclusive. For a negativeinputLengththis method returnsMAX_BLOCKSIZEalways.
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write
public void write(int b) throws java.io.IOException- Specified by:
writein classjava.io.OutputStream- Throws:
java.io.IOException
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finalize
protected void finalize() throws java.lang.ThrowableOverridden to close the stream.- Overrides:
finalizein classjava.lang.Object- Throws:
java.lang.Throwable
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finish
public void finish() throws java.io.IOException- Throws:
java.io.IOException
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close
public void close() throws java.io.IOException- Specified by:
closein interfacejava.lang.AutoCloseable- Specified by:
closein interfacejava.io.Closeable- Overrides:
closein classjava.io.OutputStream- Throws:
java.io.IOException
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flush
public void flush() throws java.io.IOException- Specified by:
flushin interfacejava.io.Flushable- Overrides:
flushin classjava.io.OutputStream- Throws:
java.io.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
public void write(byte[] buf, int offs, int len) throws java.io.IOException- Overrides:
writein classjava.io.OutputStream- Throws:
java.io.IOException
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