找出三个最大值demo

利用hadoop查询数据中三个最大值

package mr;import java.net.URI;import java.util.Arrays;import java.util.Iterator;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.IntWritable;import org.apache.hadoop.io.LongWritable;import org.apache.hadoop.io.NullWritable;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.Reducer.Context;import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;public class MyTopKClass {    static class MyTopKMapper  extends  Mapper<LongWritable, Text, Text, NullWritable>{          int[]  a=new int[3];         public void map(LongWritable k1, Text v1, Context context)                          throws java.io.IOException, java.lang.InterruptedException         {            String  lines= v1.toString().trim();            if(lines.length()==0){return;}             Arrays.sort(a);             int input=Integer.parseInt(lines);             if(a[0]<input){                 a[0]=input;             }        System.out.println("map......");         }         protected void cleanup(Context context) throws java.io.IOException, java.lang.InterruptedException{             for(int x:a)                 context.write(new Text(x+""), NullWritable.get());         }    }    private static String INPUT_PATH="hdfs://master:9000/input/topk.dat";    private static String OUTPUT_PATH="hdfs://master:9000/output/c/";    public static void main(String[] args) throws Exception {           Configuration  conf=new Configuration();        FileSystem  fs=FileSystem.get(new URI(OUTPUT_PATH),conf);        if(fs.exists(new Path(OUTPUT_PATH)))                fs.delete(new Path(OUTPUT_PATH));        Job  job=new Job(conf,"myjob");        job.setJarByClass(MyTopKClass.class);        job.setMapperClass(MyTopKMapper.class);         job.setMapOutputKeyClass(Text.class);         job.setMapOutputValueClass(NullWritable.class);        FileInputFormat.addInputPath(job,new Path(INPUT_PATH));        FileOutputFormat.setOutputPath(job, new Path(OUTPUT_PATH));        job.waitForCompletion(true);    }}