用MapReduce找共同朋友编程实现（Hadoop）

数据格式如下：

第一个字母代表本人，其他是他的朋友，找出共同朋友的人，和共同朋友是谁？

package FindFriend;

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;
import java.util.Set;
import java.util.StringTokenizer;
import java.util.TreeSet;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
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;


public class FindFriend {
    final static String INPUT_PATH = "hdfs://master:8020/liguodong/test1";
    final static String OUTPUT_PATH = "hdfs://master:8020/liguodong/test1out";

    public static void main(String[] args) throws IOException, 
    URISyntaxException, ClassNotFoundException, InterruptedException {

        Configuration conf = new Configuration();   

        final FileSystem fileSystem = FileSystem.get(new URI(INPUT_PATH),conf);     
        if(fileSystem.exists(new Path(OUTPUT_PATH)))
        {
            fileSystem.delete(new Path(OUTPUT_PATH),true);
        }

        Job job = Job.getInstance(conf,"Find friend");
        job.setJarByClass(FindFriend.class);


        job.setMapperClass(MyMapper.class);     
        job.setReducerClass(MyReducer.class);

        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(Text.class);

        FileInputFormat.addInputPath(job, new Path(INPUT_PATH));        
        FileOutputFormat.setOutputPath(job,new Path(OUTPUT_PATH));

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

    }

    static class MyMapper extends Mapper<LongWritable,Text,Text,Text>{

        @Override
        protected void map(LongWritable key, Text value, Context context)
                throws IOException, InterruptedException {
            //分割字符串
            StringTokenizer stringTokenizer = new StringTokenizer(value.toString());
            Text owner = new Text();//存放自己

            Set<String> set = new TreeSet<String>();//存放朋友

            owner.set(stringTokenizer.nextToken());
            while(stringTokenizer.hasMoreTokens()){
                set.add(stringTokenizer.nextToken());
            }

            String[] friends = new String[set.size()];//朋友
            friends = set.toArray(friends);

            for(int i=0; i<friends.length;i++){
                for(int j=i+1; j<friends.length; j++){
                    String outputkey = friends[i]+friends[j];//朋友之间两两组合
                    context.write(new Text(outputkey), owner);//<朋友组合，自己>
                }
            }
        }

    }

    static class MyReducer extends Reducer<Text, Text ,Text, Text>
    {

        @Override
        protected void reduce(Text key, Iterable<Text> values,
                Context context)
                throws IOException, InterruptedException {
            //以朋友组合作为key值，自己作为value值。
            String commonFriends = "";
            for(Text val:values)
            {
                if(commonFriends == ""){
                    commonFriends = val.toString();
                }else{
                    commonFriends = commonFriends+"--"+val.toString();
                }
            }
            context.write(key, new Text(commonFriends));
        }
    }
}

运行结果：