001 /** 002 * Licensed to the Apache Software Foundation (ASF) under one 003 * or more contributor license agreements. See the NOTICE file 004 * distributed with this work for additional information 005 * regarding copyright ownership. The ASF licenses this file 006 * to you under the Apache License, Version 2.0 (the 007 * "License"); you may not use this file except in compliance 008 * with the License. You may obtain a copy of the License at 009 * 010 * http://www.apache.org/licenses/LICENSE-2.0 011 * 012 * Unless required by applicable law or agreed to in writing, software 013 * distributed under the License is distributed on an "AS IS" BASIS, 014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 015 * See the License for the specific language governing permissions and 016 * limitations under the License. 017 */ 018 019 package org.apache.hadoop.mapreduce.lib.aggregate; 020 021 import java.util.ArrayList; 022 import java.util.Map.Entry; 023 024 import org.apache.hadoop.classification.InterfaceAudience; 025 import org.apache.hadoop.classification.InterfaceStability; 026 import org.apache.hadoop.conf.Configuration; 027 import org.apache.hadoop.io.Text; 028 029 /** 030 * This interface defines the contract a value aggregator descriptor must 031 * support. Such a descriptor can be configured with a {@link Configuration} 032 * object. Its main function is to generate a list of aggregation-id/value 033 * pairs. An aggregation id encodes an aggregation type which is used to 034 * guide the way to aggregate the value in the reduce/combiner phrase of an 035 * Aggregate based job. 036 * The mapper in an Aggregate based map/reduce job may create one or more of 037 * ValueAggregatorDescriptor objects at configuration time. For each input 038 * key/value pair, the mapper will use those objects to create aggregation 039 * id/value pairs. 040 * 041 */ 042 @InterfaceAudience.Public 043 @InterfaceStability.Stable 044 public interface ValueAggregatorDescriptor { 045 046 public static final String TYPE_SEPARATOR = ":"; 047 048 public static final Text ONE = new Text("1"); 049 050 /** 051 * Generate a list of aggregation-id/value pairs for 052 * the given key/value pair. 053 * This function is usually called by the mapper of an Aggregate based job. 054 * 055 * @param key 056 * input key 057 * @param val 058 * input value 059 * @return a list of aggregation id/value pairs. An aggregation id encodes an 060 * aggregation type which is used to guide the way to aggregate the 061 * value in the reduce/combiner phrase of an Aggregate based job. 062 */ 063 public ArrayList<Entry<Text, Text>> generateKeyValPairs(Object key, 064 Object val); 065 066 /** 067 * Configure the object 068 * 069 * @param conf 070 * a Configuration object that may contain the information 071 * that can be used to configure the object. 072 */ 073 public void configure(Configuration conf); 074 }