给一个命名为：friend.txt的文件

其中每一行中给出两个名字，中间用空格分开。（下图为文件内容）

题目：《查找出可能认识的人 》

代码如下：

RelationMapper：

package com.fesco.friend;

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

import java.io.IOException;

public class RelationMapper extends Mapper<LongWritable, Text, Text, Text> {

    @Override
    protected void map(LongWritable key, Text value, Mapper<LongWritable, Text, Text, Text>.Context context) throws IOException, InterruptedException {
        // 拆分人名
        String[] arr = value.toString().split(" ");
        context.write(new Text(arr[0]), new Text(arr[1]));
    }
}

RelationReducer ：

package com.fesco.friend;

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

import java.io.IOException;
import java.util.LinkedList;
import java.util.List;

public class RelationReducer extends Reducer<Text, Text, Text, IntWritable> {

    // 真的认识
    private static final IntWritable trueFriend = new IntWritable(1);
    // 可能认识
    private static final IntWritable fakeFriend = new IntWritable(0);

    @Override
    protected void reduce(Text key, Iterable<Text> values, Reducer<Text, Text, Text, IntWritable>.Context context) throws IOException, InterruptedException {
        // key = tom
        // values = rose jim smith lucy
        String name = key.toString();
        // 迭代器values本身是一个伪迭代器，只能迭代一次
        // 所以还需要自己定义集合来存储好友列表
        List<String> fs = new LinkedList<>();
        // 确定真实好友关系
        for (Text value : values) {
            String f = value.toString();
            fs.add(f);
            if (name.compareTo(f) <= 0) context.write(new Text(name + "-" + f), trueFriend);
            else context.write(new Text(f + "-" + name), trueFriend);
        }
        // 推测好友关系
        for (int i = 0; i < fs.size() - 1; i++) {
            String f1 = fs.get(i);
            for (int j = i + 1; j < fs.size() ; j++) {
                String f2 = fs.get(j);
                if(f1.compareTo(f2) <= 0) context.write(new Text(f1 + "-" + f2), fakeFriend);
                else context.write(new Text(f2 + "-" + f1), fakeFriend);
            }
        }

    }
}

RelatioDriver： 

package com.fesco.friend;

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.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

import java.io.IOException;

public class RelationDriver {

    public static void main(String[] args) throws IOException, InterruptedException, ClassNotFoundException {
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf);
        job.setJarByClass(RelationDriver.class);
        job.setMapperClass(RelationMapper.class);
        job.setReducerClass(RelationReducer.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(Text.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
        FileInputFormat.addInputPath(job, new Path("hdfs://10.16.3.181:9000/txt/friend.txt"));
        FileOutputFormat.setOutputPath(job, new Path("hdfs://10.16.3.181:9000/result/relation"));
        job.waitForCompletion(true);
    }
}

FriendMapper： 

package com.fesco.friend;

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

import java.io.IOException;

public class FriendMapper extends Mapper<LongWritable, Text, Text, LongWritable> {

    @Override
    protected void map(LongWritable key, Text value, Mapper<LongWritable, Text, Text, LongWritable>.Context context) throws IOException, InterruptedException {
        // 拆分数据
        String[] arr = value.toString().split("\t");
        context.write(new Text(arr[0]), new LongWritable(Long.parseLong(arr[1])));
    }
}

FriendReducer： 

package com.fesco.friend;

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

import java.io.IOException;

public class FriendReducer extends Reducer<Text, LongWritable, Text, Text> {

    @Override
    protected void reduce(Text key, Iterable<LongWritable> values, Reducer<Text, LongWritable, Text, Text>.Context context) throws IOException, InterruptedException {
        // 想要验证l两个人是否认识，验证逻辑：如果出现了数字1，说明两个人真的认识，那么就不是要找的可能认识的人
        // 如果遍历完成，全部都是数字0，那么说明这俩人真的是不认识，但是两个人有共同好友
        for (LongWritable value : values) {
            if (value.get() == 1) return ;
        }
        // 循环完成没有return，说明全部都是数字0
        String[] arr = key.toString().split("-");
        context.write(new Text(arr[0]), new Text(arr[1]));
    }
}

FriendDriver： 

package com.fesco.friend;

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.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

import java.io.IOException;

public class FriendDriver {

    public static void main(String[] args) throws IOException, InterruptedException, ClassNotFoundException {
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf);
        job.setJarByClass(FriendDriver.class);
        job.setMapperClass(FriendMapper.class);
        job.setReducerClass(FriendReducer.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(LongWritable.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(Text.class);
        FileInputFormat.addInputPath(job, new Path("hdfs://10.16.3.181:9000/result/relation"));
        FileOutputFormat.setOutputPath(job, new Path("hdfs://10.16.3.181:9000/result/friend"));
        job.waitForCompletion(true);
    }
}