loci.poi.poifs.storage

Class BlockAllocationTableReader

java.lang.Object

loci.poi.poifs.storage.BlockAllocationTableReader

public class BlockAllocationTableReader
extends Object

This class manages and creates the Block Allocation Table, which is basically a set of linked lists of block indices.

Each block of the filesystem has an index. The first block, the header, is skipped; the first block after the header is index 0, the next is index 1, and so on.

A block's index is also its index into the Block Allocation Table. The entry that it finds in the Block Allocation Table is the index of the next block in the linked list of blocks making up a file, or it is set to -2: end of list.

Author:

Marc Johnson (mjohnson at apache dot org)

Field Summary

Fields

Modifier and Type	Field and Description
private IntList	_entries

Constructor Summary

Constructors

Constructor and Description
BlockAllocationTableReader() Constructor BlockAllocationTableReader
BlockAllocationTableReader(int block_count, int[] block_array, int xbat_count, int xbat_index, BlockList raw_block_list, int size) create a BlockAllocationTableReader for an existing filesystem.
BlockAllocationTableReader(ListManagedBlock[] blocks, BlockList raw_block_list, int size) create a BlockAllocationTableReader from an array of raw data blocks

Method Summary

Methods

Modifier and Type	Method and Description
(package private) ListManagedBlock[]	fetchBlocks(int startBlock, BlockList blockList) walk the entries from a specified point and return the associated blocks.
(package private) int	getNextBlockIndex(int index) return the next block index
(package private) boolean	isUsed(int index) determine whether the block specified by index is used or not
private void	setEntries(ListManagedBlock[] blocks, BlockList raw_blocks, int size) Convert an array of blocks into a set of integer indices

Methods inherited from class java.lang.Object

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

Field Detail

_entries

private IntList _entries

Constructor Detail

BlockAllocationTableReader

public BlockAllocationTableReader(int block_count,
                          int[] block_array,
                          int xbat_count,
                          int xbat_index,
                          BlockList raw_block_list,
                          int size)
                           throws IOException

create a BlockAllocationTableReader for an existing filesystem. Side effect: when this method finishes, the BAT blocks will have been removed from the raw block list, and any blocks labeled as 'unused' in the block allocation table will also have been removed from the raw block list.

Parameters:

block_count - the number of BAT blocks making up the block allocation table

block_array - the array of BAT block indices from the filesystem's header

xbat_count - the number of XBAT blocks

xbat_index - the index of the first XBAT block

raw_block_list - the list of RawDataBlocks

Throws:

IOException - if, in trying to create the table, we encounter logic errors

BlockAllocationTableReader

BlockAllocationTableReader(ListManagedBlock[] blocks,
                          BlockList raw_block_list,
                          int size)
                     throws IOException

create a BlockAllocationTableReader from an array of raw data blocks

Parameters:

blocks - the raw data

raw_block_list - the list holding the managed blocks

Throws:

IOException

BlockAllocationTableReader

BlockAllocationTableReader()

Constructor BlockAllocationTableReader

Method Detail

fetchBlocks

ListManagedBlock[] fetchBlocks(int startBlock,
                             BlockList blockList)
                         throws IOException

walk the entries from a specified point and return the associated blocks. The associated blocks are removed from the block list

Parameters:

startBlock - the first block in the chain

blockList - the raw data block list

Returns:

array of ListManagedBlocks, in their correct order

Throws:

IOException - if there is a problem acquiring the blocks

isUsed

boolean isUsed(int index)

determine whether the block specified by index is used or not

Parameters:

index - index of block in question

Returns:

true if the specific block is used, else false

getNextBlockIndex

int getNextBlockIndex(int index)
                throws IOException

return the next block index

Parameters:

index - of the current block

Returns:

index of the next block (may be POIFSConstants.END_OF_CHAIN, indicating end of chain (duh))

Throws:

IOException - if the current block is unused

setEntries

private void setEntries(ListManagedBlock[] blocks,
              BlockList raw_blocks,
              int size)
                 throws IOException

Convert an array of blocks into a set of integer indices

Parameters:

blocks - the array of blocks containing the indices

raw_blocks - the list of blocks being managed. Unused blocks will be eliminated from the list

Throws:

IOException