| /** |
| * 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 org.apache.hadoop.mapreduce.lib.aggregate; |
| |
| import java.util.ArrayList; |
| import java.util.Map.Entry; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| import org.apache.hadoop.conf.Configuration; |
| import org.apache.hadoop.io.Text; |
| |
| /** |
| * This interface defines the contract a value aggregator descriptor must |
| * support. Such a descriptor can be configured with a {@link Configuration} |
| * 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. |
| * |
| */ |
| @InterfaceAudience.Public |
| @InterfaceStability.Stable |
| public interface ValueAggregatorDescriptor { |
| |
| public static final String TYPE_SEPARATOR = ":"; |
| |
| public static final Text ONE = new Text("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<Text, Text>> generateKeyValPairs(Object key, |
| Object val); |
| |
| /** |
| * Configure the object |
| * |
| * @param conf |
| * a Configuration object that may contain the information |
| * that can be used to configure the object. |
| */ |
| public void configure(Configuration conf); |
| } |