@SuppressWarnings("unchecked")
  @Override
  public void write(Writable w) throws IOException {
    dbRecordWriter.write((DBRecordWritable) w, null);
  }
JdbcRecordWriter is wrapper class to write data to the underlying database.
jdbc-handler/src/main/java/org/apache/hive/storage/jdbc/JdbcRecordWriter.java