blockallocationtablereader.java

Office格式转换代码

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2003 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache POI" must not be used to endorse or promote products
 *    derived from this software without prior written permission. For
 *    written permission, please contact [e-mail].
 *
 * 5. Products derived from this software may not be called "Apache",
 *    "Apache POI", nor may "Apache" appear in their name, without
 *    prior written permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

package org.apache.poi.poifs.storage;

import java.io.IOException;
import java.io.OutputStream;

import java.util.*;

import org.apache.poi.poifs.common.POIFSConstants;
import org.apache.poi.util.IntList;
import org.apache.poi.util.LittleEndian;
import org.apache.poi.util.LittleEndianConsts;

/**
 * This class manages and creates the Block Allocation Table, which is
 * basically a set of linked lists of block indices.
 * <P>
 * 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.
 * <P>
 * 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)
 */

public class BlockAllocationTableReader
{
    private IntList _entries;

    /**
     * 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.
     *
     * @param block_count the number of BAT blocks making up the block
     *                    allocation table
     * @param block_array the array of BAT block indices from the
     *                    filesystem's header
     * @param xbat_count the number of XBAT blocks
     * @param xbat_index the index of the first XBAT block
     * @param raw_block_list the list of RawDataBlocks
     *
     * @exception IOException if, in trying to create the table, we
     *            encounter logic errors
     */

    public BlockAllocationTableReader(final int block_count,
                                      final int [] block_array,
                                      final int xbat_count,
                                      final int xbat_index,
                                      final BlockList raw_block_list)
        throws IOException
    {
        this();
        if (block_count <= 0)
        {
            throw new IOException(
                "Illegal block count; minimum count is 1, got " + block_count
                + " instead");
        }

        // acquire raw data blocks containing the BAT block data
        RawDataBlock blocks[] = new RawDataBlock[ block_count ];
        int          limit    = Math.min(block_count, block_array.length);
        int          block_index;

        for (block_index = 0; block_index < limit; block_index++)
        {
            blocks[ block_index ] =
                ( RawDataBlock ) raw_block_list
                    .remove(block_array[ block_index ]);
        }
        if (block_index < block_count)
        {

            // must have extended blocks
            if (xbat_index < 0)
            {
                throw new IOException(
                    "BAT count exceeds limit, yet XBAT index indicates no valid entries");
            }
            int chain_index           = xbat_index;
            int max_entries_per_block = BATBlock.entriesPerXBATBlock();
            int chain_index_offset    = BATBlock.getXBATChainOffset();

            for (int j = 0; j < xbat_count; j++)
            {
                limit = Math.min(block_count - block_index,
                                 max_entries_per_block);
                byte[] data   = raw_block_list.remove(chain_index).getData();
                int    offset = 0;

                for (int k = 0; k < limit; k++)
                {
                    blocks[ block_index++ ] =
                        ( RawDataBlock ) raw_block_list
                            .remove(LittleEndian.getInt(data, offset));
                    offset                  += LittleEndianConsts.INT_SIZE;
                }
                chain_index = LittleEndian.getInt(data, chain_index_offset);
                if (chain_index == POIFSConstants.END_OF_CHAIN)
                {
                    break;
                }
            }
        }
        if (block_index != block_count)
        {
            throw new IOException("Could not find all blocks");
        }

        // now that we have all of the raw data blocks, go through and
        // create the indices
        setEntries(blocks, raw_block_list);
    }

    /**
     * create a BlockAllocationTableReader from an array of raw data blocks
     *
     * @param blocks the raw data
     * @param raw_block_list the list holding the managed blocks
     *
     * @exception IOException
     */

    BlockAllocationTableReader(final ListManagedBlock [] blocks,
                               final BlockList raw_block_list)
        throws IOException
    {
        this();
        setEntries(blocks, raw_block_list);
    }

    /**
     * Constructor BlockAllocationTableReader
     *
     *
     */

    BlockAllocationTableReader()
    {
        _entries = new IntList();
    }

    /**
     * walk the entries from a specified point and return the
     * associated blocks. The associated blocks are removed from the
     * block list
     *
     * @param startBlock the first block in the chain
     * @param blockList the raw data block list
     *
     * @return array of ListManagedBlocks, in their correct order
     *
     * @exception IOException if there is a problem acquiring the blocks
     */

    ListManagedBlock [] fetchBlocks(final int startBlock,
                                    final BlockList blockList)
        throws IOException
    {
        List blocks       = new ArrayList();
        int  currentBlock = startBlock;

        while (currentBlock != POIFSConstants.END_OF_CHAIN)
        {
            blocks.add(blockList.remove(currentBlock));
            currentBlock = _entries.get(currentBlock);
        }
        return ( ListManagedBlock [] ) blocks
            .toArray(new ListManagedBlock[ 0 ]);
    }

    // methods for debugging reader

    /**
     * determine whether the block specified by index is used or not
     *
     * @param index index of block in question
     *
     * @return true if the specific block is used, else false
     */

    boolean isUsed(final int index)
    {
        boolean rval = false;

        try
        {
            rval = _entries.get(index) != -1;
        }
        catch (IndexOutOfBoundsException ignored)
        {
        }
        return rval;
    }

    /**
     * return the next block index
     *
     * @param index of the current block
     *
     * @return index of the next block (may be
     *         POIFSConstants.END_OF_CHAIN, indicating end of chain
     *         (duh))
     *
     * @exception IOException if the current block is unused
     */

    int getNextBlockIndex(final int index)
        throws IOException
    {
        if (isUsed(index))
        {
            return _entries.get(index);
        }
        else
        {
            throw new IOException("index " + index + " is unused");
        }
    }

    /**
     * Convert an array of blocks into a set of integer indices
     *
     * @param blocks the array of blocks containing the indices
     * @param raw_blocks the list of blocks being managed. Unused
     *                   blocks will be eliminated from the list
     *
     * @exception IOException
     */

    private void setEntries(final ListManagedBlock [] blocks,
                            final BlockList raw_blocks)
        throws IOException
    {
        int limit = BATBlock.entriesPerBlock();

        for (int block_index = 0; block_index < blocks.length; block_index++)
        {
            byte[] data   = blocks[ block_index ].getData();
            int    offset = 0;

            for (int k = 0; k < limit; k++)
            {
                int entry = LittleEndian.getInt(data, offset);

                if (entry == POIFSConstants.UNUSED_BLOCK)
                {
                    raw_blocks.zap(_entries.size());
                }
                _entries.add(entry);
                offset += LittleEndianConsts.INT_SIZE;
            }

            // discard block
            blocks[ block_index ] = null;
        }
        raw_blocks.setBAT(this);
    }
}   // end class BlockAllocationTableReader