CBZip2OutputStream (Starlink-UK API)

java.lang.Object
- java.io.OutputStream
- - uk.ac.starlink.util.bzip2.CBZip2OutputStream

All Implemented Interfaces:: Closeable, Flushable, AutoCloseable, BZip2Constants

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 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 uk.ac.starlink.util.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(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

All Methods Static Methods Instance Methods Concrete 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()`
`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, finalize, 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(OutputStream out)
                   throws 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:
    
    IOException - if an I/O error occurs in the specified stream.
    
    NullPointerException - if out == null.
  - CBZip2OutputStream
```
public CBZip2OutputStream(OutputStream out,
                          int blockSize)
                   throws 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:
    
    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
  - 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 - int
    
    maxLen - int
  - 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 IOException
```
    Specified by:
    
    write in class OutputStream
    
    Throws:
    
    IOException
  - finish
```
public void finish()
            throws IOException
```
    Throws:
    
    IOException
  - close
```
public void close()
           throws IOException
```
    Specified by:
    
    close in interface Closeable
    
    Specified by:
    
    close in interface AutoCloseable
    
    Overrides:
    
    close in class OutputStream
    
    Throws:
    
    IOException
  - flush
```
public void flush()
           throws IOException
```
    Specified by:
    
    flush in interface Flushable
    
    Overrides:
    
    flush in class OutputStream
    
    Throws:
    
    IOException
  - getBlockSize
```
public final int getBlockSize()
```
    Returns the blocksize parameter specified at construction time.
    
    Returns:
    
    int
  - write
```
public void write(byte[] buf,
                  int offs,
                  int len)
           throws IOException
```
    Overrides:
    
    write in class OutputStream
    
    Throws:
    
    IOException

Class CBZip2OutputStream

Field Summary

Fields inherited from interface uk.ac.starlink.util.bzip2.BZip2Constants

Constructor Summary

Method Summary

Methods inherited from class java.io.OutputStream

Methods inherited from class java.lang.Object

Field Detail

MIN_BLOCKSIZE

MAX_BLOCKSIZE

SETMASK

CLEARMASK

GREATER_ICOST

LESSER_ICOST

SMALL_THRESH

DEPTH_THRESH

WORK_FACTOR

QSORT_STACK_SIZE

Constructor Detail

CBZip2OutputStream

CBZip2OutputStream

Method Detail

hbMakeCodeLengths

chooseBlockSize

write

finish

close

flush

getBlockSize

write