@Override
  public void checkOutputSpecs(JobContext context) throws IOException, InterruptedException {
    // we can't know ahead of time if it's going to blow up when the user
    // passes a table name that doesn't exist, so nothing useful here.
  }
Writes an action (Put or Delete) to the specified table. the table being updated. the update,
either a put or a delete. if the action is not a put or a delete.
hbase-mapreduce/src/main/java/org/apache/hadoop/hbase/mapreduce/MultiTableOutputFormat.java