cd ~/srcmkdir classesjavac -classpath ~/hadoop-0.20.2/hadoop-0.20.2-core.jar WordCount.java -d classesjar -cvf WordCount.jar -C classes/ .hadoop jar WordCount.jar com.codestyle.hadoop.WordCount input outputhadoop fs -ls outputhadoop fs -cat output/part-00000

要点：

编译WordCount.java时必须通过classpath指定hadoop的库文件。指定源码输出到classes目录

打包class文件成为jar文件

通过hadoop调用jar文件执行MapReduce, 内容输出到output目录 （如果该目录存在，则要先删掉这个目录）在命令参数中必须指定包名+类名

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WordCount.java

package com.codestyle.hadoop;import java.io.IOException;import java.util.*;import org.apache.hadoop.fs.Path;import org.apache.hadoop.conf.*;import org.apache.hadoop.io.*;import org.apache.hadoop.mapred.*;import org.apache.hadoop.util.*;public class WordCount {   public static class Map extends MapReduceBase implements Mapper
     
       {     private final static IntWritable one = new IntWritable(1);     private Text word = new Text();     public void map(LongWritable key, Text value, OutputCollector
      
        output, Reporter reporter) throws IOException {       String line = value.toString();       StringTokenizer tokenizer = new StringTokenizer(line);       while (tokenizer.hasMoreTokens()) {         word.set(tokenizer.nextToken());         output.collect(word, one);       }     }   }   public static class Reduce extends MapReduceBase implements Reducer
       
         {     public void reduce(Text key, Iterator
        
          values, OutputCollector
         
           output, Reporter reporter) throws IOException {       int sum = 0;       while (values.hasNext()) {         sum += values.next().get();       }       output.collect(key, new IntWritable(sum));     }   }   public static void main(String[] args) throws Exception {     JobConf conf = new JobConf(WordCount.class);     conf.setJobName("wordcount");     conf.setOutputKeyClass(Text.class);     conf.setOutputValueClass(IntWritable.class);     conf.setMapperClass(Map.class);     conf.setReducerClass(Reduce.class);     conf.setInputFormat(TextInputFormat.class);     conf.setOutputFormat(TextOutputFormat.class);     FileInputFormat.setInputPaths(conf, new Path(args[0]));     FileOutputFormat.setOutputPath(conf, new Path(args[1]));     JobClient.runJob(conf);   }}
         
        
       
      
     

查看执行结果

lishujun@lishujun-virtual-machine:~/src$ hadoop fs -cat output/part-00000Hadoop    1Hello    2World    1

 

参考资料：