| /** |
| * 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.lang.reflect.Constructor; |
| 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 class implements a wrapper for a user defined value |
| * aggregator descriptor. |
| * It serves two functions: One is to create an object of |
| * ValueAggregatorDescriptor from the name of a user defined class |
| * that may be dynamically loaded. The other is to |
| * delegate invocations of generateKeyValPairs function to the created object. |
| * |
| */ |
| @InterfaceAudience.Public |
| @InterfaceStability.Stable |
| public class UserDefinedValueAggregatorDescriptor implements |
| ValueAggregatorDescriptor { |
| private String className; |
| |
| protected ValueAggregatorDescriptor theAggregatorDescriptor = null; |
| |
| private static final Class<?>[] argArray = new Class[] {}; |
| |
| /** |
| * Create an instance of the given class |
| * @param className the name of the class |
| * @return a dynamically created instance of the given class |
| */ |
| public static Object createInstance(String className) { |
| Object retv = null; |
| try { |
| ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); |
| Class<?> theFilterClass = Class.forName(className, true, classLoader); |
| Constructor<?> meth = theFilterClass.getDeclaredConstructor(argArray); |
| meth.setAccessible(true); |
| retv = meth.newInstance(); |
| } catch (Exception e) { |
| throw new RuntimeException(e); |
| } |
| return retv; |
| } |
| |
| private void createAggregator(Configuration conf) { |
| if (theAggregatorDescriptor == null) { |
| theAggregatorDescriptor = (ValueAggregatorDescriptor) |
| createInstance(this.className); |
| theAggregatorDescriptor.configure(conf); |
| } |
| } |
| |
| /** |
| * |
| * @param className the class name of the user defined descriptor class |
| * @param conf a configure object used for decriptor configuration |
| */ |
| public UserDefinedValueAggregatorDescriptor(String className, |
| Configuration conf) { |
| this.className = className; |
| this.createAggregator(conf); |
| } |
| |
| /** |
| * Generate a list of aggregation-id/value pairs for the given |
| * key/value pairs by delegating the invocation to the real object. |
| * |
| * @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) { |
| ArrayList<Entry<Text, Text>> retv = new ArrayList<Entry<Text, Text>>(); |
| if (this.theAggregatorDescriptor != null) { |
| retv = this.theAggregatorDescriptor.generateKeyValPairs(key, val); |
| } |
| return retv; |
| } |
| |
| /** |
| * @return the string representation of this object. |
| */ |
| public String toString() { |
| return "UserDefinedValueAggregatorDescriptor with class name:" + "\t" |
| + this.className; |
| } |
| |
| /** |
| * Do nothing. |
| */ |
| public void configure(Configuration conf) { |
| |
| } |
| |
| } |