WordCount.java
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上传日期:2018-01-08
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- /**
- * 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;
- import java.io.IOException;
- import java.util.ArrayList;
- import java.util.Iterator;
- import java.util.List;
- import java.util.StringTokenizer;
- import org.apache.hadoop.conf.Configuration;
- import org.apache.hadoop.conf.Configured;
- import org.apache.hadoop.fs.Path;
- import org.apache.hadoop.io.IntWritable;
- import org.apache.hadoop.io.LongWritable;
- import org.apache.hadoop.io.Text;
- import org.apache.hadoop.mapred.FileInputFormat;
- import org.apache.hadoop.mapred.FileOutputFormat;
- import org.apache.hadoop.mapred.JobClient;
- import org.apache.hadoop.mapred.JobConf;
- import org.apache.hadoop.mapred.MapReduceBase;
- import org.apache.hadoop.mapred.Mapper;
- import org.apache.hadoop.mapred.OutputCollector;
- import org.apache.hadoop.mapred.Reducer;
- import org.apache.hadoop.mapred.Reporter;
- import org.apache.hadoop.util.Tool;
- import org.apache.hadoop.util.ToolRunner;
- /**
- * This is an example Hadoop Map/Reduce application.
- * It reads the text input files, breaks each line into words
- * and counts them. The output is a locally sorted list of words and the
- * count of how often they occurred.
- *
- * To run: bin/hadoop jar build/hadoop-examples.jar wordcount
- * [-m <i>maps</i>] [-r <i>reduces</i>] <i>in-dir</i> <i>out-dir</i>
- */
- public class WordCount extends Configured implements Tool {
-
- /**
- * Counts the words in each line.
- * For each line of input, break the line into words and emit them as
- * (<b>word</b>, <b>1</b>).
- */
- public static class MapClass extends MapReduceBase
- implements Mapper<LongWritable, Text, Text, IntWritable> {
-
- private final static IntWritable one = new IntWritable(1);
- private Text word = new Text();
-
- public void map(LongWritable key, Text value,
- OutputCollector<Text, IntWritable> output,
- Reporter reporter) throws IOException {
- String line = value.toString();
- StringTokenizer itr = new StringTokenizer(line);
- while (itr.hasMoreTokens()) {
- word.set(itr.nextToken());
- output.collect(word, one);
- }
- }
- }
-
- /**
- * A reducer class that just emits the sum of the input values.
- */
- public static class Reduce extends MapReduceBase
- implements Reducer<Text, IntWritable, Text, IntWritable> {
-
- public void reduce(Text key, Iterator<IntWritable> values,
- OutputCollector<Text, IntWritable> output,
- Reporter reporter) throws IOException {
- int sum = 0;
- while (values.hasNext()) {
- sum += values.next().get();
- }
- output.collect(key, new IntWritable(sum));
- }
- }
-
- static int printUsage() {
- System.out.println("wordcount [-m <maps>] [-r <reduces>] <input> <output>");
- ToolRunner.printGenericCommandUsage(System.out);
- return -1;
- }
-
- /**
- * The main driver for word count map/reduce program.
- * Invoke this method to submit the map/reduce job.
- * @throws IOException When there is communication problems with the
- * job tracker.
- */
- public int run(String[] args) throws Exception {
- JobConf conf = new JobConf(getConf(), WordCount.class);
- conf.setJobName("wordcount");
-
- // the keys are words (strings)
- conf.setOutputKeyClass(Text.class);
- // the values are counts (ints)
- conf.setOutputValueClass(IntWritable.class);
-
- conf.setMapperClass(MapClass.class);
- conf.setCombinerClass(Reduce.class);
- conf.setReducerClass(Reduce.class);
-
- List<String> other_args = new ArrayList<String>();
- for(int i=0; i < args.length; ++i) {
- try {
- if ("-m".equals(args[i])) {
- conf.setNumMapTasks(Integer.parseInt(args[++i]));
- } else if ("-r".equals(args[i])) {
- conf.setNumReduceTasks(Integer.parseInt(args[++i]));
- } else {
- other_args.add(args[i]);
- }
- } catch (NumberFormatException except) {
- System.out.println("ERROR: Integer expected instead of " + args[i]);
- return printUsage();
- } catch (ArrayIndexOutOfBoundsException except) {
- System.out.println("ERROR: Required parameter missing from " +
- args[i-1]);
- return printUsage();
- }
- }
- // Make sure there are exactly 2 parameters left.
- if (other_args.size() != 2) {
- System.out.println("ERROR: Wrong number of parameters: " +
- other_args.size() + " instead of 2.");
- return printUsage();
- }
- FileInputFormat.setInputPaths(conf, other_args.get(0));
- FileOutputFormat.setOutputPath(conf, new Path(other_args.get(1)));
-
- JobClient.runJob(conf);
- return 0;
- }
-
-
- public static void main(String[] args) throws Exception {
- int res = ToolRunner.run(new Configuration(), new WordCount(), args);
- System.exit(res);
- }
- }