MapReduce实例

1.WordCount（统计单词）

经典的运用MapReuce编程模型的实例

1.1 Description

给定一系列的单词/数据，输出每个单词/数据的数量

1.2 Sample

1 a is b is not c
2 b is a is not d

1.3 Output

1 a:2
2 b:2
3 c:1
4 d:1
5 is:4
6 not:2

1.4 Solution

  1 /**
  2  *  Licensed under the Apache License, Version 2.0 (the "License");
  3  *  you may not use this file except in compliance with the License.
  4  *  You may obtain a copy of the License at
  5  *
  6  *      http://www.apache.org/licenses/LICENSE-2.0
  7  *
  8  *  Unless required by applicable law or agreed to in writing, software
  9  *  distributed under the License is distributed on an "AS IS" BASIS,
 10  *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 11  *  See the License for the specific language governing permissions and
 12  *  limitations under the License.
 13  */    
 14 
 15 package org.apache.hadoop.examples;
 16 
 17 import java.io.File;
 18 import java.io.IOException;
 19 import java.util.StringTokenizer;
 20 
 21 import org.apache.hadoop.conf.Configuration;
 22 import org.apache.hadoop.fs.Path;
 23 import org.apache.hadoop.io.IntWritable;
 24 import org.apache.hadoop.io.Text;
 25 import org.apache.hadoop.mapreduce.Job;
 26 import org.apache.hadoop.mapreduce.Mapper;
 27 import org.apache.hadoop.mapreduce.Reducer;
 28 import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
 29 import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
 30 import org.apache.hadoop.util.GenericOptionsParser;
 31 
 32 public class WordCount {
 33     
 34   //map输出的<key,value>为<输入的单词/数据,1>即<Text,IntWritable>
 35   public static class TokenizerMapper 
 36        extends Mapper<Object, Text, Text, IntWritable>{
 37     //value为封装好的int即IntWritable
 38     private final static IntWritable one = new IntWritable(1);
 39     private Text word = new Text();
 40 
 41     public void map(Object key, Text value, Context context
 42                     ) throws IOException, InterruptedException {
 43       StringTokenizer itr = new StringTokenizer(value.toString());
 44       while (itr.hasMoreTokens()) {
 45         word.set(itr.nextToken());//word为每个单词/数据,以空格为分隔符识别
 46         context.write(word, one);
 47       }
 48     }
 49   }
 50   
 51   //reduce输入的<key,value>为<输入的单词/数据,各个值的1相加即sum(实际是一个list)>
 52   //即<Text,IntWrite>
 53   public static class IntSumReducer 
 54        extends Reducer<Text,IntWritable,Text,IntWritable> {  
 55     private IntWritable result = new IntWritable();
 56 
 57     public void reduce(Text key, Iterable<IntWritable> values, 
 58                        Context context
 59                        ) throws IOException, InterruptedException {
 60       int sum = 0;
 61       for (IntWritable val : values) {
 62         sum += val.get();
 63       }
 64       result.set(sum);
 65       context.write(key, result);
 66     }
 67   }
 68 
 69   public static void main(String[] args) throws Exception {
 70     Configuration conf = new Configuration();
 71     String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
 72     if (otherArgs.length != 2) {
 73       System.err.println("Usage: wordcount <in> <out>");
 74       System.exit(2);
 75     }
 76     //删除已存在的输出文件夹
 77     judgeFileExist(otherArgs[1]);
 78     Job job = new Job(conf, "word count");
 79     job.setJarByClass(WordCount.class);
 80     job.setMapperClass(TokenizerMapper.class);
 81     job.setCombinerClass(IntSumReducer.class);
 82     job.setReducerClass(IntSumReducer.class);
 83     job.setOutputKeyClass(Text.class);
 84     job.setOutputValueClass(IntWritable.class);
 85     FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
 86     FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
 87     System.exit(job.waitForCompletion(true) ? 0 : 1);
 88   }
 89   
 90   //删除文件夹及其目录下的文件
 91   public static void judgeFileExist(String path){
 92       File file = new File(path);
 93       if( file.exists() ){
 94           deleteFileDir(file);
 95       }
 96   }
 97   
 98   public static void deleteFileDir(File path){
 99       if( path.isDirectory() ){
100           String[] files = path.list();
101           for( int i=0;i<files.length;i++ ){
102               deleteFileDir( new File(path,files[i]) );
103           }
104       }
105       path.delete();
106   }
107   
108 }

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