import java.io.IOException;
import java.util.StringTokenizer;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;

public class WordCount{
        public static class TokenizerMapper extends Mapper<Object,Text,Text,IntWritable>{
                private final static IntWritable one = new IntWritable(1);
                private Text word = new Text();

                public void map(Object key, Text value, Context context) throws IOException,InterruptedException{
                        StringTokenizer itr = new StringTokenizer(value.toString());
                        while (itr.hasMoreTokens()){
                                word.set(itr.nextToken());
                                context.write(word,one);
                        }
                }
        }


        public static class IntSumReducer extends Reducer<Text,IntWritable,Text,IntWritable>{
                private IntWritable result = new IntWritable();
                public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException,InterruptedException{
                        int sum = 0;
                        for (IntWritable val : values)
                        {
                                sum += val.get();
                        }
                        result.set(sum);
                        context.write(key,result);
                }
        }

        public static void main(String[] args) throws Exception{
                Configuration conf = new Configuration();
                String[] otherArgs = new GenericOptionsParser(conf,args).getRemainingArgs();
                if (otherArgs.length != 2)
                {
                        System.err.println("Usage: wordcount <in> <out>");
                        System.exit(2);
                }
                Job job = new Job(conf,"word count");
                job.setJarByClass(WordCount.class);
                job.setMapperClass(TokenizerMapper.class);
                job.setCombinerClass(IntSumReducer.class);
                job.setReducerClass(IntSumReducer.class);
                job.setOutputKeyClass(Text.class);
                job.setOutputValueClass(IntWritable.class);
                FileInputFormat.addInputPath(job,new Path(otherArgs[0]));
                FileOutputFormat.setOutputPath(job,new Path(otherArgs[1]));
                System.exit(job.waitForCompletion(true)?0:1);
        }
}
 

編譯java原始碼

[[email protected] code]$ javac -classpath /usr/local/hadoop/hadoop-core-1.2.1.jar:/usr/local/hadoop/lib/commons-cli-1.2.jar WordCount.java

[[email protected] code]$ jar -cvf wordcount.jar *.class

[[email protected] code]$ ./bin/hadoop jar ./code/wordcount.jar WordCount input/ output/
 

[[email protected] code]$ ./bin/hadoop fs -cat output/*