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
019package org.apache.hadoop.mapred.lib.aggregate;
020
021import org.apache.hadoop.classification.InterfaceAudience;
022import org.apache.hadoop.classification.InterfaceStability;
023import org.apache.hadoop.mapred.JobConf;
024
025/**
026 * This class implements a wrapper for a user defined value aggregator 
027 * descriptor.
028 * It serves two functions: One is to create an object of 
029 * ValueAggregatorDescriptor from the name of a user defined class that may be 
030 * dynamically loaded. The other is to delegate invocations of 
031 * generateKeyValPairs function to the created object.
032 */
033@InterfaceAudience.Public
034@InterfaceStability.Stable
035public class UserDefinedValueAggregatorDescriptor extends org.apache.hadoop.
036    mapreduce.lib.aggregate.UserDefinedValueAggregatorDescriptor
037    implements ValueAggregatorDescriptor {
038
039  /**
040   * Create an instance of the given class
041   * @param className the name of the class
042   * @return a dynamically created instance of the given class 
043   */
044  public static Object createInstance(String className) {
045    return org.apache.hadoop.mapreduce.lib.aggregate.
046      UserDefinedValueAggregatorDescriptor.createInstance(className);
047  }
048
049  /**
050   * 
051   * @param className the class name of the user defined descriptor class
052   * @param job a configure object used for decriptor configuration
053   */
054  public UserDefinedValueAggregatorDescriptor(String className, JobConf job) {
055    super(className, job);
056    ((ValueAggregatorDescriptor)theAggregatorDescriptor).configure(job);
057  }
058
059  /**
060   *  Do nothing.
061   */
062  public void configure(JobConf job) {
063
064  }
065
066}