Map端

package com.yd.CommFriend;

import java.io.IOException;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class CommMapper extends Mapper<LongWritable, Text, Text, Text>{
	
	@Override
	protected void map
 
(LongWritable key, Text value, Context context)
			throws IOException, InterruptedException {
			//A:N,K,L資料格式 A 和他的朋友
		String[] split = value.toString().split(":");
		//key表示本人，value是他的朋友們
		context.write(new Text(split[0]), new Text(split[1]));
	}

}

Reduce端

package com.yd.CommFriend;

import java.
 
io.IOException;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

import MR.OrderBean;

public
 
 class CommReducer extends Reducer<Text, Text, Text, Text>{
	List<List<String>> personAndFriends = new ArrayList<>();
	@Override
	protected void reduce(Text key, Iterable<Text> values, Reducer<Text, Text, Text, Text>.Context context)
			throws IOException, InterruptedException {
		//其實迭代器中只有一個值
		for(Text t : values) {
			String[] split = t.toString().split(",");
			List<String> friends = new ArrayList<>();
			//第一個是本人，其餘的都是他的好友
			friends.add(0,key.toString());
			for(String s: split) {
				friends.add(s);
			}
			System.out.println(friends);
			
			personAndFriends.add(friends);
			
		}
	}
	
	
	
	@Override
	protected void cleanup(Context context) throws IOException, InterruptedException {
		personAndFriends.sort((ls1,ls2)->{return ls1.get(0).compareTo(ls2.get(0));});
		
		Map<String,String> map = new HashMap<>();
		
		for(int i=0;i< personAndFriends.size();i++) {
			//取出一個人和他的好友
			List<String> begin = personAndFriends.get(i);
			String beginPerson = begin.get(0);// 取出本人
			System.out.println(beginPerson+":"+begin);
			//迴圈其他集合，看看是不是有共同好友
			for(int j=i+1 ; j< personAndFriends.size();j++) {
				List<String> back = personAndFriends.get(j);
				String backPerson = back.get(0);
				//Comparator<OrderBean> c = (a,b)->{return 0;};
				//begin.sort((s1,s2)->{return s1.compareTo(s2);});
				//back.sort((s1,s2)->{return s1.compareTo(s2);});
				
				for(String friend : back) {
			//A:N,K,L
			//N:P,A
			//上面這種情況是不算共同好友的		if(begin.contains(friend)&&!friend.equals(beginPerson)&&!friend.equals(backPerson)) {
						String pp = beginPerson+"-"+backPerson;
						if(map.containsKey(pp)) {
							String value = map.get(pp)+","+friend;
							map.remove(pp);
							map.put(pp, value);
						}else {
							map.put(pp, friend);
						}
					}
				}
				
				
				
			}
			
		}
		
	//把結果輸出
		Set<Entry<String,String>> entrySet = map.entrySet();
		for(Entry<String,String> es: entrySet) {
			context.write(new Text(es.getKey()), new Text(es.getValue()));
		}
		
		
		
	}
	
	
	

}

Driver端

package com.yd.CommFriend;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.CombineTextInputFormat;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;



public class CommDriver {
	public static void main(String[] args) throws Exception {
		Configuration conf = new Configuration();
		Job job = Job.getInstance(conf);
		job.setJarByClass(CommDriver.class);
		job.setInputFormatClass(CombineTextInputFormat.class);
		job.setMapperClass(CommMapper.class);
		job.setReducerClass(CommReducer.class);
		job.setMapOutputKeyClass(Text.class);
		job.setMapOutputValueClass(Text.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(Text.class);
		
		FileInputFormat.setInputPaths(job, new Path("D:\\friend"));
		FileOutputFormat.setOutputPath(job, new Path("D:\\outFriends"));
		job.waitForCompletion(true);
		
	}

}