private synchronized ResultScannerWrapper getScanner(int id) {
    return scannerMap.getIfPresent(id);
  }
Returns the scanner associated with the specified ID.
@param id the ID of the scanner to get
@return a Scanner, or null if ID was invalid.
hbase-thrift/src/main/java/org/apache/hadoop/hbase/thrift/ThriftHBaseServiceHandler.java