Hadoop MapReduce 简单案例--求平均值

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.LongWritable;
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 Sum {

public static class SumMapper extends
Mapper<Object, Text, Text, LongWritable> {
private Text word = new Text("sum");
private static LongWritable numValue = new LongWritable(1);
public void map(Object key, Text value, Context context)
throws IOException, InterruptedException {
StringTokenizer itr = new StringTokenizer(value.toString());
long sum = 0,sum2=0;  //sum为每次读入的数，sun2为每行的个数
while (itr.hasMoreTokens()) {
String s = itr.nextToken();
long val = Long.parseLong(s);
sum += val;
sum2++;
}
numValue.set(sum/sum2);
word.set("average");
context.write(word, numValue);
}
}
public static class SumReducer extends
Reducer<Text, LongWritable, Text, LongWritable> {
private LongWritable result = new LongWritable();
private Text ave = new Text("average");
public void reduce(Text key, Iterable<LongWritable> values,
Context context) throws IOException, InterruptedException {
long sum = 0,count=0;  //sum为每行计算出来的平均值，count为行数
for (LongWritable val : values) {
long v = val.get();
sum += v;
count++;
}
result.set(sum/count);
context.write(ave, 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: numbersum <in> <out>");
System.exit(2);
}
long startTime=System.currentTimeMillis();//计算时间
Job job = new Job(conf, "number sum");
job.setJarByClass(Sum.class);
job.setMapperClass(SumMapper.class);
job.setReducerClass(SumReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(LongWritable.class);
FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
job.waitForCompletion(true) ;
long endTime=System.currentTimeMillis();
System.out.println("time="+(endTime-startTime));
System.exit(0);
}
}