UserDefinedValueAggregatorDescriptor.java
上传用户:quxuerui
上传日期:2018-01-08
资源大小:41811k
文件大小:4k
源码类别:
网格计算
开发平台:
Java
- /**
- * 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.mapred.lib.aggregate;
- import java.lang.reflect.Constructor;
- import java.util.ArrayList;
- import java.util.Map.Entry;
- import org.apache.hadoop.io.Text;
- import org.apache.hadoop.mapred.JobConf;
- /**
- * This class implements a wrapper for a user defined value aggregator descriptor.
- * It servs 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
- * deligate inviokations of generateKeyValPairs function to the created object.
- *
- */
- public class UserDefinedValueAggregatorDescriptor implements
- ValueAggregatorDescriptor {
- private String className;
- private 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(JobConf job) {
- if (theAggregatorDescriptor == null) {
- theAggregatorDescriptor = (ValueAggregatorDescriptor) createInstance(this.className);
- theAggregatorDescriptor.configure(job);
- }
- }
- /**
- *
- * @param className the class name of the user defined descriptor class
- * @param job a configure object used for decriptor configuration
- */
- public UserDefinedValueAggregatorDescriptor(String className, JobConf job) {
- this.className = className;
- this.createAggregator(job);
- }
- /**
- * 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(JobConf job) {
- }
- }