import org.apache.hadoop.hbase.util.RegionSizeCalculator; //导入依赖的package包/类
/**
 * Calculates the splits that will serve as input for the map tasks. The
 * number of splits matches the number of regions in a table.
 *
 * @param context The current job context.
 * @return The list of input splits.
 * @throws IOException When creating the list of splits fails.
 * @see org.apache.hadoop.mapreduce.InputFormat#getSplits(org.apache.hadoop.mapreduce.JobContext)
 */
@Override
public List<InputSplit> getSplits(JobContext context) throws IOException {
  if (scans.isEmpty()) {
    throw new IOException("No scans were provided.");
  }
  List<InputSplit> splits = new ArrayList<InputSplit>();

  for (Scan scan : scans) {
    byte[] tableName = scan.getAttribute(Scan.SCAN_ATTRIBUTES_TABLE_NAME);
    if (tableName == null) 
      throw new IOException("A scan object did not have a table name");

    HTable table = null;
    try {
      table = new HTable(context.getConfiguration(), tableName);
      Pair<byte[][], byte[][]> keys = table.getStartEndKeys();
      if (keys == null || keys.getFirst() == null ||
          keys.getFirst().length == 0) {
        throw new IOException("Expecting at least one region for table : "
            + Bytes.toString(tableName));
      }
      int count = 0;

      byte[] startRow = scan.getStartRow();
      byte[] stopRow = scan.getStopRow();

      RegionSizeCalculator sizeCalculator = new RegionSizeCalculator(table);

      for (int i = 0; i < keys.getFirst().length; i++) {
        if (!includeRegionInSplit(keys.getFirst()[i], keys.getSecond()[i])) {
          continue;
        }
        HRegionLocation hregionLocation = table.getRegionLocation(keys.getFirst()[i], false);
        String regionHostname = hregionLocation.getHostname();
        HRegionInfo regionInfo = hregionLocation.getRegionInfo();
      
        // determine if the given start and stop keys fall into the range
        if ((startRow.length == 0 || keys.getSecond()[i].length == 0 ||
            Bytes.compareTo(startRow, keys.getSecond()[i]) < 0) &&
            (stopRow.length == 0 ||
                Bytes.compareTo(stopRow, keys.getFirst()[i]) > 0)) {
          byte[] splitStart =
              startRow.length == 0 ||
                  Bytes.compareTo(keys.getFirst()[i], startRow) >= 0 ? keys
                  .getFirst()[i] : startRow;
          byte[] splitStop =
              (stopRow.length == 0 || Bytes.compareTo(keys.getSecond()[i],
                  stopRow) <= 0) && keys.getSecond()[i].length > 0 ? keys
                  .getSecond()[i] : stopRow;

          long regionSize = sizeCalculator.getRegionSize(regionInfo.getRegionName());
          TableSplit split =
              new TableSplit(table.getName(),
                  scan, splitStart, splitStop, regionHostname, regionSize);

          splits.add(split);
          if (LOG.isDebugEnabled())
            LOG.debug("getSplits: split -> " + (count++) + " -> " + split);
        }
      }
    } finally {
      if (null != table) table.close();
    }
  }
  return splits;
}