org.apache.jcs.auxiliary.disk.block
Class BlockDisk

java.lang.Object
  org.apache.jcs.auxiliary.disk.block.BlockDisk

public class BlockDisk
extends java.lang.Object

This class manages reading an writing data to disk. When asked to write a value, it returns a block array. It can read an object from the block numbers in a byte array.

Author:

Aaron Smuts

Field Summary

static byte

HEADER_SIZE_BYTES The size of the header that indicates the amount of data stored in an occupied block.

Constructor Summary

BlockDisk(java.io.File file)
Constructor for the Disk object

BlockDisk(java.io.File file, int blockSizeBytes)
Creates the file and set the block size in bytes.

Method Summary

protected int	calculateByteOffsetForBlock(int block) Calcuates the file offset for a particular block.
protected int	calculateTheNumberOfBlocksNeeded(byte[] data) The number of blocks needed.
protected void	close() Closes the raf.
protected void	freeBlocks(int[] blocksToFree) Add these blocks to the emptyBlock list.
protected long	getAveragePutSizeBytes()
protected byte[][]	getBlockChunks(byte[] complete, int numBlocksNeeded) Return the amount to put in each block.
protected int	getBlockSizeBytes()
protected int	getEmptyBlocks()
protected int	getNumberOfBlocks()
protected long	length() Returns the raf length.
protected java.io.Serializable	read(int[] blockNumbers) Reads an object that is located in the specified blocks.
protected static byte[]	serialize(java.io.Serializable obj) Returns the serialized form of the given object in a byte array.
java.lang.String	toString() For debugging only.
protected int[]	write(java.io.Serializable object) This writes an object to disk and returns the blocks it was stored in.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

HEADER_SIZE_BYTES

public static final byte HEADER_SIZE_BYTES

The size of the header that indicates the amount of data stored in an occupied block.

See Also:

Constant Field Values

Constructor Detail

BlockDisk

public BlockDisk(java.io.File file)
          throws java.io.FileNotFoundException

Constructor for the Disk object

Parameters:

file -

Throws:

java.io.FileNotFoundException

BlockDisk

public BlockDisk(java.io.File file,
                 int blockSizeBytes)
          throws java.io.FileNotFoundException

Creates the file and set the block size in bytes.

Parameters:

file -

blockSizeBytes -

Throws:

java.io.FileNotFoundException

Method Detail

write

protected int[] write(java.io.Serializable object)
               throws java.io.IOException

This writes an object to disk and returns the blocks it was stored in.

The program flow is as follows:

1. Serialize the object.
2. Detemine the number of blocks needed.
3. Look for free blocks in the emptyBlock list.
4. If there were not enough in the empty list. Take the nextBlock and increment it.
5. If the data will not fit in one block, create sub arrays.
6. Write the subarrays to disk.
7. If the process fails we should decrement the block count if we took from it.

Parameters:

object -

Returns:

the blocks we used.

Throws:

java.io.IOException

getBlockChunks

protected byte[][] getBlockChunks(byte[] complete,
                                  int numBlocksNeeded)

Return the amount to put in each block. Fill them all the way, minus the header.

Parameters:

complete -

numBlocksNeeded -

Returns:

byte[][]

read

protected java.io.Serializable read(int[] blockNumbers)
                             throws java.io.IOException,
                                    java.lang.ClassNotFoundException

Reads an object that is located in the specified blocks.

Parameters:

blockNumbers -

Returns:

Serializable

Throws:

java.io.IOException

java.lang.ClassNotFoundException

freeBlocks

protected void freeBlocks(int[] blocksToFree)

Add these blocks to the emptyBlock list.

Parameters:

blocksToFree -

calculateByteOffsetForBlock

protected int calculateByteOffsetForBlock(int block)

Calcuates the file offset for a particular block.

Parameters:

block -

Returns:

the offset for this block

calculateTheNumberOfBlocksNeeded

protected int calculateTheNumberOfBlocksNeeded(byte[] data)

The number of blocks needed.

Parameters:

data -

Returns:

the number of blocks needed to store the byte array

length

protected long length()
               throws java.io.IOException

Returns the raf length.

Returns:

the size of the file.

Throws:

java.io.IOException

close

protected void close()
              throws java.io.IOException

Closes the raf.

Throws:

java.io.IOException

serialize

protected static byte[] serialize(java.io.Serializable obj)
                           throws java.io.IOException

Returns the serialized form of the given object in a byte array.

Use the Serilizer abstraction layer.

Parameters:

obj -

Returns:

a byte array of the serialized object.

Throws:

java.io.IOException

getNumberOfBlocks

protected int getNumberOfBlocks()

Returns:

Returns the numberOfBlocks.

getBlockSizeBytes

protected int getBlockSizeBytes()

Returns:

Returns the blockSizeBytes.

getAveragePutSizeBytes

protected long getAveragePutSizeBytes()

Returns:

Returns the average size of the an element inserted.

getEmptyBlocks

protected int getEmptyBlocks()

Returns:

Returns the number of empty blocks.

toString

public java.lang.String toString()

For debugging only.

Overrides:

toString in class java.lang.Object

Returns:

String with details.