Package org.apache.commons.jcs3.auxiliary.disk.block

Class BlockDisk

java.lang.Object

org.apache.commons.jcs3.auxiliary.disk.block.BlockDisk

All Implemented Interfaces:

AutoCloseable

public class BlockDisk
extends Object
implements AutoCloseable

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.

Field Summary

Fields

Modifier and Type	Field	Description
static final byte	HEADER_SIZE_BYTES	The size of the header that indicates the amount of data stored in an occupied block.

Constructor Summary

Constructors

Constructor	Description
BlockDisk(File file, int blockSizeBytes)	Creates the file and set the block size in bytes.
BlockDisk(File file, int blockSizeBytes, IElementSerializer elementSerializer)	Creates the file and set the block size in bytes.
BlockDisk(File file, IElementSerializer elementSerializer)	Constructor for the Disk object

Method Summary

Modifier and Type	Method	Description
protected long	calculateByteOffsetForBlockAsLong(int block)	Calculates the file offset for a particular block.
protected int	calculateTheNumberOfBlocksNeeded(byte[] data)	The number of blocks needed.
void	close()	Closes the file.
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 String	getFilePath()	This is used for debugging.
protected int	getNumberOfBlocks()
protected long	length()	Returns the file length.
protected <T> T	read(int[] blockNumbers)	Reads an object that is located in the specified blocks.
protected void	reset()	Resets the file.
String	toString()	For debugging only.
protected <T> int[]	write(T 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 Details

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 Details

BlockDisk

public BlockDisk(File file,
 IElementSerializer elementSerializer)
          throws IOException

Constructor for the Disk object

Parameters:

file -

elementSerializer -

Throws:

IOException

BlockDisk

public BlockDisk(File file,
 int blockSizeBytes)
          throws IOException

Creates the file and set the block size in bytes.

Parameters:

file -

blockSizeBytes -

Throws:

IOException

BlockDisk

public BlockDisk(File file,
 int blockSizeBytes,
 IElementSerializer elementSerializer)
          throws IOException

Creates the file and set the block size in bytes.

Parameters:

file -

blockSizeBytes -

elementSerializer -

Throws:

IOException

Method Details

write

protected <T> int[] write(T object)
                   throws 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. Determine 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:

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 <T> T read(int[] blockNumbers)
              throws IOException,
ClassNotFoundException

Reads an object that is located in the specified blocks.

Parameters:

blockNumbers -

Returns:

the object instance

Throws:

IOException

ClassNotFoundException

freeBlocks

protected void freeBlocks(int[] blocksToFree)

Add these blocks to the emptyBlock list.

Parameters:

blocksToFree -

calculateByteOffsetForBlockAsLong

protected long calculateByteOffsetForBlockAsLong(int block)

Calculates the file offset for a particular block.

Parameters:

block - number

Returns:

the byte offset for this block in the file as a long

Since:

2.0

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 IOException

Returns the file length.

Returns:

the size of the file.

Throws:

IOException

close

public void close()
           throws IOException

Closes the file.

Specified by:

close in interface AutoCloseable

Throws:

IOException

reset

protected void reset()
              throws IOException

Resets the file.

Throws:

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 String toString()

For debugging only.

Overrides:

toString in class Object

Returns:

String with details.

getFilePath

protected String getFilePath()

This is used for debugging.

Returns:

the file path.