compoundfile.java

来自「jexcelapi_2_4, JXL的API, JXL是JAVA读取EXCEL的」· Java 代码 · 共 553 行 · 第 1/2 页

/*********************************************************************
*
*      Copyright (C) 2002 Andrew Khan
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
***************************************************************************/

package jxl.write.biff;

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

import common.Assert;
import jxl.biff.BaseCompoundFile;
import jxl.biff.IntegerHelper;

/**
 * Writes out a compound file
 * 
 * Header block is -1
 * Excel data is e..n (where is the head extension blocks, normally 0 and
 * n is at least 8)
 * Summary information (8 blocks)
 * Document summary (8 blocks)
 * BBD is block p..q (where p=e+n+16 and q-p+1 is the number of BBD blocks)
 * Property storage block is q+b...r (normally 1 block) (where b is the number
 * of BBD blocks)
 */
final class CompoundFile extends BaseCompoundFile
{
  /**
   * The stream to which the jumbled up data is written to
   */
  private OutputStream out;
  /**
   * The organized biff records which form the actual excel data
   */
  private byte[] excelData;

  /**
   * The size of the array
   */
  private int    size;

  /**
   * The size the excel data should be in order to comply with the
   * general compound file format
   */
  private int    requiredSize;

  /**
   * The number of blocks it takes to store the big block depot
   */
  private int numBigBlockDepotBlocks;

  /**
   * The number of extension blocks required for the header to describe
   * the BBD
   */
  private int numExtensionBlocks;

  /**
   * The extension block for the header
   */
  private int extensionBlock;

  /**
   * The number of blocks it takes to store the excel data
   */
  private int excelDataBlocks;

  /**
   * The start block of the root entry
   */
  private int rootStartBlock;

  /**
   * The start block of the excel data
   */
  private int excelDataStartBlock;

  /**
   * The start block of the big block depot
   */
  private int bbdStartBlock;

  // The following member variables are used across methods when
  // writing out the big block depot
  /**
   * The current position within the bbd.  Used when writing out the
   * BBD
   */
  private int bbdPos;

  /**
   * The current bbd block
   */
  private byte[] bigBlockDepot;

  /**
   * Constructor
   * 
   * @param l the length of the data
   * @param os the output stream to write to
   * @param data the excel data
   */
  public CompoundFile(byte[] data, int l, OutputStream os)
  {
    super();
    size = l;
    excelData = data;

    int blocks  = (l / BIG_BLOCK_SIZE) + 1;

    // First pad the data out so that it fits nicely into a whole number
    // of blocks
    if (l < SMALL_BLOCK_THRESHOLD)
    {
      requiredSize = SMALL_BLOCK_THRESHOLD;
    }
    else
    {
      requiredSize = blocks * BIG_BLOCK_SIZE;
    }
    
    out = os;

    // Do the calculations
    excelDataBlocks = requiredSize/BIG_BLOCK_SIZE;

    int blockChainLength = (BIG_BLOCK_SIZE - BIG_BLOCK_DEPOT_BLOCKS_POS)/4;

    int totalBlocks = excelDataBlocks +
      8 + // summary block
      8 + // document information
      1 + // root entry
      1;  // the BBD block

    // Calculate the number of BBD blocks needed to hold this info
    numBigBlockDepotBlocks = (int) Math.ceil( (double) totalBlocks / 
                                              (double) (BIG_BLOCK_SIZE/4));

    // Does this affect the total?
    totalBlocks += numBigBlockDepotBlocks;

    // And recalculate
    numBigBlockDepotBlocks = (int) Math.ceil( (double) totalBlocks / 
                                              (double) (BIG_BLOCK_SIZE/4));

    // See if the excel bbd chain can fit into the header block.
    // Remember to allow for the  end of chain indicator
    if (numBigBlockDepotBlocks > blockChainLength - 1 )
    {
      // Sod it - we need an extension block.  We have to go through
      // the whole tiresome calculation again
      extensionBlock = 0;

      // Compute the number of extension blocks
      int bbdBlocksLeft = numBigBlockDepotBlocks - blockChainLength + 1;

      numExtensionBlocks = (int) Math.ceil((double) bbdBlocksLeft /
                                           (double) (BIG_BLOCK_SIZE/4 - 1));

      // Modify the total number of blocks required and recalculate the
      // the number of bbd blocks
      totalBlocks += numExtensionBlocks;
      numBigBlockDepotBlocks = (int) Math.ceil( (double) totalBlocks / 
                                                (double) (BIG_BLOCK_SIZE/4));
    }
    else
    {
      extensionBlock = -2;
      numExtensionBlocks = 0;
    }

    // Set the excel data start block to be after the header (and
    // its extensions)
    excelDataStartBlock = numExtensionBlocks;
    
    // Set the bbd start block to be after all the excel data
    bbdStartBlock = excelDataStartBlock + excelDataBlocks + 16;

    // Set the root start block to be after all the big block depot blocks
    rootStartBlock = excelDataStartBlock + excelDataBlocks + 
                     16 + numBigBlockDepotBlocks;
  }

  /**
   * Writes out the excel file in OLE compound file format
   * 
   * @exception IOException 
   */
  public void write() throws IOException
  {
    writeHeader();
    writeExcelData();
    writeBigBlockDepot();
    writePropertySets();

    // Don't flush or close the stream - this is handled by the enclosing File
    // object
  }

  /**
   * Writes out the excel data, padding it out with empty bytes as
   * necessary
   * 
   * @exception IOException 
   */
  private void writeExcelData() throws IOException
  {
    out.write(excelData, 0, size);

    byte[] padding = new byte[requiredSize - size];
    out.write(padding);

    padding = new byte[SMALL_BLOCK_THRESHOLD];
    // Write out the summary information
    out.write(padding);
    
    // Write out the document summary
    out.write(padding);
  }

  /**
   * Writes the compound file header
   * 
   * @exception IOException 
   */
  private void writeHeader() throws IOException
  {
    // Build up the header array
    byte[] headerBlock = new byte[BIG_BLOCK_SIZE];
    byte[] extensionBlockData = new byte[BIG_BLOCK_SIZE * numExtensionBlocks];

    // Copy in the identifier
    System.arraycopy(IDENTIFIER, 0, headerBlock, 0, IDENTIFIER.length);

    // Copy in some magic values - no idea what they mean
    headerBlock[0x18] = 0x3e;
    headerBlock[0x1a] = 0x3;
    headerBlock[0x1c] = (byte) 0xfe;
    headerBlock[0x1d] = (byte) 0xff;
    headerBlock[0x1e] = 0x9;
    headerBlock[0x20] = 0x6;
    headerBlock[0x39] = 0x10;

    // Set the number of BBD blocks
    IntegerHelper.getFourBytes(numBigBlockDepotBlocks, 
                               headerBlock, 
                               NUM_BIG_BLOCK_DEPOT_BLOCKS_POS);  

    // Set the small block depot block to -2 ie. there is no
    // small block depot
    IntegerHelper.getFourBytes(-2,
                               headerBlock,
                               SMALL_BLOCK_DEPOT_BLOCK_POS);

    // Set the extension block 
    IntegerHelper.getFourBytes(extensionBlock,
                               headerBlock,
                               EXTENSION_BLOCK_POS);

    // Set the number of extension blocks to be the number of BBD blocks - 1
    IntegerHelper.getFourBytes(numExtensionBlocks,