以下是qq的好友列表数据，冒号前是一个用户，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？

c --> a  b  e  f g  h  k （第一步：找出c的所有共同好友）
a-b  c
a-e  c  （第二步：作为key,即可得到a-e的共同好友c和d）d --> a  c  e  f g  h  k
a-c  d
a-e  d

package cn.bigdata.hdfs.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<LongWritable, Text, Text, Text>{@Overrideprotected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {//A:B,C,D,F,E,O(找出具有共同好友的都是哪些人的)String line = value.toString();String[] person_friends = line.split(":");String person = person_friends[0];String feiends = person_friends[1];for(String friend : feiends.split(",")){// 输出<好友，人>context.write(new Text(friend), new Text(person));}}}static class SharedFriendsStepOneReducer extends Reducer<Text, Text, Text, Text>{@Overrideprotected void reduce(Text friend, Iterable<Text> persons, Context context) throws IOException, InterruptedException {//persons:具有共同好友的所有人：c --> a b e f g h k 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(args[0]));FileOutputFormat.setOutputPath(job, new Path(args[1]));job.waitForCompletion(true);}
}

A    I,K,C,B,G,F,H,O,D,
B    A,F,J,E,
C    A,E,B,H,F,G,K,
D    G,C,K,A,L,F,E,H,
E    G,M,L,H,A,F,B,D,
F    L,M,D,C,G,A,
G    M,
H    O,
I    O,C,
J    O,
K    B,
L    D,E,
M    E,F,
O    A,H,I,J,F,

package cn.bigdata.hdfs.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<LongWritable, Text, Text, Text> {// 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
        @Overrideprotected 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(",");//排序，使得B-C和C-B不重复
            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<Text, Text, Text, Text> {@Overrideprotected void reduce(Text person_person, Iterable<Text> 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("F:/fensiOutput/part-r-00000"));FileOutputFormat.setOutputPath(job, new Path("F:/fensiOutput4"));job.waitForCompletion(true);}
}

A-B    E C
A-C    D F
A-D    E F
A-E    D B C
A-F    O B C D E
A-G    F E C D
A-H    E C D O
A-I    O
A-J    O B
A-K    D C
A-L    F E D
A-M    E F
B-C    A
B-D    A E
B-E    C
B-F    E A C
B-G    C E A
B-H    A E C
B-I    A
B-K    C A
B-L    E
B-M    E
B-O    A
C-D    A F
C-E    D
C-F    D A
C-G    D F A
C-H    D A
C-I    A
C-K    A D
C-L    D F
C-M    F
C-O    I A
D-E    L
D-F    A E
D-G    E A F
D-H    A E
D-I    A
D-K    A
D-L    E F
D-M    F E
D-O    A
E-F    D M C B
E-G    C D
E-H    C D
E-J    B
E-K    C D
E-L    D
F-G    D C A E
F-H    A D O E C
F-I    O A
F-J    B O
F-K    D C A
F-L    E D
F-M    E
F-O    A
G-H    D C E A
G-I    A
G-K    D A C
G-L    D F E
G-M    E F
G-O    A
H-I    O A
H-J    O
H-K    A C D
H-L    D E
H-M    E
H-O    A
I-J    O
I-K    A
I-O    A
K-L    D
K-O    A
L-M    E F