wordcount的mr java代码

package wordcount;

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> {
// define the constant number ONE
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);
}
}
}

/**
* the reducer class calculate the count sum of each word
* INPUT: KEY: text VALUE: IntWritable
* OUTPUT:KEY:text VALUE: IntWritable
*/
public static class IntSumReducer extends Reducer<Text, IntWritable, Text, IntWritable> {
private IntWritable result = new IntWritable();
// values are the set of each node or file
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);
}
}

/**
*
* @param args
* @throws Exception
*             one arguments is the input path the other arguments is the
*             output path
*/
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 = Job.getInstance(conf, "Word count");
job.setJarByClass(WordCount.class);
job.setJobName("Word count test");

job.setMapperClass(TokenizerMapper.class);

// combiner use the same method as reducer and calculate the local count
// sum
job.setCombinerClass(IntSumReducer.class);

// reducer task get the total count of each word
job.setReducerClass(IntSumReducer.class);

// set the output KEY and VALUE type
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);

// use the arguments to set the job input and output path
FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));

System.exit(job.waitForCompletion(true) ? 0 : 1);
}
}