content: /**
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you under the Apache License, Version 2.0 (the
   * "License"); you may not use this file except in compliance
   * with the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package com.aliyun.odps.mapred.example.local.lib.aggregate;
  
  import java.util.ArrayList;
  import java.util.Map.Entry;
  
  import com.aliyun.odps.mapred.conf.JobConf;
  
  /**
   * This interface defines the contract a value aggregator descriptor must
   * support. Such a descriptor can be configured with a JobConf object. Its main
   * function is to generate a list of aggregation-id/value pairs. An aggregation
   * id encodes an aggregation type which is used to guide the way to aggregate
   * the value in the reduce/combiner phrase of an Aggregate based job.The mapper
   * in an Aggregate based map/reduce job may create one or more of
   * ValueAggregatorDescriptor objects at configuration time. For each input
   * key/value pair, the mapper will use those objects to create aggregation
   * id/value pairs.
   */
  public interface ValueAggregatorDescriptor {
  
    public static final String TYPE_SEPARATOR = ":";
    public static final String ONE = "1";
  
    /**
     * Generate a list of aggregation-id/value pairs for the given key/value pair.
     * This function is usually called by the mapper of an Aggregate based job.
     *
     * @param key
     *     input key
     * @param val
     *     input value
     * @return a list of aggregation id/value pairs. An aggregation id encodes an
     * aggregation type which is used to guide the way to aggregate the
     * value in the reduce/combiner phrase of an Aggregate based job.
     */
    public ArrayList<Entry<String, String>> generateKeyValPairs(Object key,
                                                                Object val);
  
    /**
     * Configure the object
     *
     * @param job
     *     a JobConf object that may contain the information that can be used
     *     to configure the object.
     */
    public void configure(JobConf job);
  }
  