@Override
  public boolean next(ImmutableBytesWritable key, Result value) throws IOException {
    return this.recordReaderImpl.next(key, value);
  }
@param key   HStoreKey as input key.
@param value MapWritable as input value
@return true if there was more data
hbase-mapreduce/src/main/java/org/apache/hadoop/hbase/mapred/TableRecordReader.java