writablerecorddata.java

一个非常有用的操作MCRSOFT EXCEL文件的工具。可以用JAVA方便的新建

/*********************************************************************
*
*      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.biff;

import common.Assert;
import common.Logger;

import jxl.read.biff.Record;

/**
 * Extension of the standard RecordData which is used to support those
 * records which, once read, may also be written
 */
public abstract class WritableRecordData extends RecordData
                                         implements ByteData
{
  /**
   * The logger
   */
  private static Logger logger = Logger.getLogger(WritableRecordData.class);
  /**
   * The maximum length allowed by Excel for any record length
   */
  protected static final int maxRecordLength = 8228;

  /**
   * Constructor used by the writable records
   *
   * @param t the biff type of this record
   */
  protected WritableRecordData(Type t)
  {
    super(t);
  }

  /**
   * Constructor used when reading a record
   *
   * @param t the raw data read from the biff file
   */
  protected WritableRecordData(Record t)
  {
    super(t);
  }

  /**
   * Used when writing out records.  This portion of the method handles the
   * biff code and the length of the record and appends on the data retrieved
   * from the subclasses
   *
   * @return the full record data to be written out to the compound file
   */
  public final byte[] getBytes()
  {
    byte[] data = getData();

    int dataLength = data.length;

    // Don't the call the automatic continuation code for now
    //    Assert.verify(dataLength <= maxRecordLength - 4);
    // If the bytes length is greater than the max record length
    // then split out the data set into continue records
    if (data.length > maxRecordLength - 4)
    {
      dataLength = maxRecordLength - 4;
      data = handleContinueRecords(data);
    }

    byte[]  bytes = new byte[data.length + 4];

    System.arraycopy(data, 0, bytes, 4, data.length);

    IntegerHelper.getTwoBytes(getCode(), bytes, 0);
    IntegerHelper.getTwoBytes(dataLength, bytes, 2);

    return bytes;
  }

  /**
   * The number of bytes for this record exceeds the maximum record
   * length, so a continue is required
   * @param data the raw data
   * @return  the continued data
   */
  private byte[] handleContinueRecords(byte[] data)
  {
    // Deduce the number of continue records
    int continuedData = data.length - (maxRecordLength - 4);
    int numContinueRecords = continuedData / (maxRecordLength - 4) + 1;

    // Create the new byte array, allowing for the continue records
    // code and length
    byte[] newdata = new byte[data.length + numContinueRecords * 4];

    // Copy the bona fide record data into the beginning of the super
    // record
    System.arraycopy(data, 0, newdata, 0, maxRecordLength - 4);
    int oldarraypos = maxRecordLength - 4;
    int newarraypos = maxRecordLength - 4;

    // Now handle all the continue records
    for (int i = 0; i < numContinueRecords; i++)
    {
      // The number of bytes to add into the new array
      int length = Math.min(data.length - oldarraypos, maxRecordLength - 4);

      // Add in the continue record code
      IntegerHelper.getTwoBytes(Type.CONTINUE.value, newdata, newarraypos);
      IntegerHelper.getTwoBytes(length, newdata, newarraypos + 2);

      // Copy in as much of the new data as possible
      System.arraycopy(data, oldarraypos, newdata, newarraypos + 4, length);

      // Update the position counters
      oldarraypos += length;
      newarraypos += length + 4;
    }

    return newdata;
  }

  /**
   * Abstract method called by the getBytes method.  Subclasses implement
   * this method to incorporate their specific binary data - excluding the
   * biff code and record length, which is handled by this class
   *
   * @return subclass specific biff data
   */
  protected abstract byte[] getData();
}