Hadoop案例（三）找博客共同好友

找博客共同好友案例

1）数据准备

以下是博客的好友列表数据，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

多对多的关系
数据库：学生       课程        成绩表
学生表和课程表的自然连接

A
A   

A : B
A : C
B : C

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

A-B  C,D

friends.txt

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？

2）需求分析

先求出A、B、C、….等是谁的好友

第一次输出结果

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,

第二次输出结果

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

3）代码实现

（1）第一次Mapper

package com.xyg.mapreduce.friends;
import java.io.IOException;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

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

    @Override
    protected void map(LongWritable key, Text value, Mapper<LongWritable, Text, Text, Text>.Context context)
            throws IOException, InterruptedException {
        // 1 获取一行 A:B,C,D,F,E,O
        String line = value.toString();

        // 2 切割
        String[] fileds = line.split(":");

        // 3 获取person和好友
        String person = fileds[];
        String[] friends = fileds[].split(",");

        // 4写出去
        for(String friend: friends){
            // 输出 <好友，人>
            context.write(new Text(friend), new Text(person));
        }
    }
}

（2）第一次Reducer

package com.xyg.mapreduce.friends;
import java.io.IOException;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

public class OneShareFriendsReducer extends Reducer<Text, Text, Text, Text>{

    @Override
    protected void reduce(Text key, Iterable<Text> values, Context context)
            throws IOException, InterruptedException {

        StringBuffer sb = new StringBuffer();
        //1 拼接
        for(Text person: values){
            sb.append(person).append(",");
        }

        //2 写出
        context.write(key, new Text(sb.toString()));
    }
}

（3）第一次Driver

package com.xyg.mapreduce.friends;
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.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class OneShareFriendsDriver {

    public static void main(String[] args) throws Exception {
        // 1 获取job对象
        Configuration configuration = new Configuration();
        Job job = Job.getInstance(configuration);

        // 2 指定jar包运行的路径
        job.setJarByClass(OneShareFriendsDriver.class);

        // 3 指定map/reduce使用的类
        job.setMapperClass(OneShareFriendsMapper.class);
        job.setReducerClass(OneShareFriendsReducer.class);

        // 4 指定map输出的数据类型
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(Text.class);

        // 5 指定最终输出的数据类型
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(Text.class);

        // 6 指定job的输入原始所在目录
        FileInputFormat.setInputPaths(job, new Path(args[]));
        FileOutputFormat.setOutputPath(job, new Path(args[]));

        // 7 提交
        boolean result = job.waitForCompletion(true);

        System.exit(result?:);
    }
}

（4）第二次Mapper

package com.xyg.mapreduce.friends;
import java.io.IOException;
import java.util.Arrays;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

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

    @Override
    protected void map(LongWritable key, Text value, Context context)
            throws IOException, InterruptedException {
        // A I,K,C,B,G,F,H,O,D,
        // 友 人，人，人
        String line = value.toString();
        String[] friend_persons = line.split("\t");

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

        Arrays.sort(persons);

        for (int i = ; i < persons.length - ; i++) {

            for (int j = i + ; 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));
            }
        }
    }
}

（5）第二次Reducer

package com.xyg.mapreduce.friends;
import java.io.IOException;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

public class TwoShareFriendsReducer extends Reducer<Text, Text, Text, Text>{

    @Override
    protected void reduce(Text key, Iterable<Text> values, Context context)
            throws IOException, InterruptedException {

        StringBuffer sb = new StringBuffer();

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

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

（6）第二次Driver

package com.xyg.mapreduce.friends;

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

public class TwoShareFriendsDriver {

    public static void main(String[] args) throws Exception {
        // 1 获取job对象
        Configuration configuration = new Configuration();
        Job job = Job.getInstance(configuration);

        // 2 指定jar包运行的路径
        job.setJarByClass(TwoShareFriendsDriver.class);

        // 3 指定map/reduce使用的类
        job.setMapperClass(TwoShareFriendsMapper.class);
        job.setReducerClass(TwoShareFriendsReducer.class);

        // 4 指定map输出的数据类型
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(Text.class);

        // 5 指定最终输出的数据类型
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(Text.class);

        // 6 指定job的输入原始所在目录
        FileInputFormat.setInputPaths(job, new Path(args[]));
        FileOutputFormat.setOutputPath(job, new Path(args[]));

        // 7 提交
        boolean result = job.waitForCompletion(true);

        System.exit(result?:);
    }
}