（mr案例）---- 社交粉丝数据，找出两两之间的共同好友

以下是qq的好友列表数据，冒号前是一个用，冒号后是该用户的所有好友（数据中的好友关系是单向的）

A:B,C,D,F,E,O

B:A,C,E,K

C:F,A,D,I

D:A,E,F,L

E:B,C,D,M,L

F:A,B,C,D,E,O,M

G:A,C,D,E,F

H:A,C,D,E,O

I:A,O

J:B,O

K:A,C,D

L:D,E,F

M:E,F,G

O:A,H,I,J

 

求出哪些人两两之间有共同好友，及他俩的共同好友都有谁？

package cn.itcast.bigdata.mr.fensi;

import java.io.IOException;


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;


public class SharedFriendsStepOne {


static class SharedFriendsStepOneMapper extends Mapper {


@Override
protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
// A:B,C,D,F,E,O
String line = value.toString();
String[] person_friends = line.split(":");
String person = person_friends[0];
String friends = person_friends[1];


for (String friend : friends.split(",")) {


// 输出<好友，人>
context.write(new Text(friend), new Text(person));
}


}


}


static class SharedFriendsStepOneReducer extends Reducer {


@Override
protected void reduce(Text friend, Iterable persons, Context context) throws IOException, InterruptedException {


StringBuffer sb = new StringBuffer();


for (Text person : persons) {
sb.append(person).append(",");


}
context.write(friend, new Text(sb.toString()));
}


}


public static void main(String[] args) throws Exception {


Configuration conf = new Configuration();


Job job = Job.getInstance(conf);
job.setJarByClass(SharedFriendsStepOne.class);


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

job.setMapperClass(SharedFriendsStepOneMapper.class);
job.setReducerClass(SharedFriendsStepOneReducer.class);


FileInputFormat.setInputPaths(job, new Path("D:/srcdata/friends"));
FileOutputFormat.setOutputPath(job, new Path("D:/temp/out"));


job.waitForCompletion(true);


}

}

package cn.itcast.bigdata.mr.fensi;


import java.io.IOException;
import java.util.Arrays;


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;


public class SharedFriendsStepTwo {


static class SharedFriendsStepTwoMapper extends Mapper {


// 拿到的数据是上一个步骤的输出结果
// A I,K,C,B,G,F,H,O,D,
// 友 人，人，人
@Override
protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {


String line = value.toString();
String[] friend_persons = line.split("\t");


String friend = friend_persons[0];
String[] persons = friend_persons[1].split(",");


Arrays.sort(persons);


for (int i = 0; i < persons.length - 1; i++) {
for (int j = i + 1; j < persons.length; j++) {
// 发出 <人-人，好友> ，这样，相同的“人-人”对的所有好友就会到同1个reduce中去
context.write(new Text(persons[i] + "-" + persons[j]), new Text(friend));
}


}


}


}


static class SharedFriendsStepTwoReducer extends Reducer {


@Override
protected void reduce(Text person_person, Iterable friends, Context context) throws IOException, InterruptedException {


StringBuffer sb = new StringBuffer();


for (Text friend : friends) {
sb.append(friend).append(" ");


}
context.write(person_person, new Text(sb.toString()));
}


}


public static void main(String[] args) throws Exception {


Configuration conf = new Configuration();


Job job = Job.getInstance(conf);
job.setJarByClass(SharedFriendsStepTwo.class);


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


job.setMapperClass(SharedFriendsStepTwoMapper.class);
job.setReducerClass(SharedFriendsStepTwoReducer.class);


FileInputFormat.setInputPaths(job, new Path("D:/temp/out/part-r-00000"));
FileOutputFormat.setOutputPath(job, new Path("D:/temp/out2"));


job.waitForCompletion(true);


}


}