MapReduce练习之共同好友

0. 问题

1. 通过mapreduce找出用户A,B,C…中每两个人所共同拥有的好友都有谁
2. 输入文件
   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
3. 输出文件格式为: 用户-用户 共同好友
   A-H E C D O
   A-I O
   A-J O B

1. 主方法

public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
    Configuration cfg=new Configuration();      
    Job job = Job.getInstance(cfg);
    //设置主方法所在类
    job.setJarByClass(friend.class);
    job.setMapperClass(FriendMaper.class);
    job.setReducerClass(FriendReduceer.class);
    //job的输出key-value
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(Text.class);
    job.setMapOutputKeyClass(Text.class);
    job.setMapOutputValueClass(Text.class);
    //输入路径和输出路径的设置
    FileInputFormat.addInputPath(job, new Path("d:\\mr\\input\\friend"));
    FileOutputFormat.setOutputPath(job, new Path("d:\\mr\\outfriend"));
    System.exit(job.waitForCompletion(true)?0:1);
}

2. map

static class FriendMaper extends Mapper<LongWritable,Text,Text,Text>{
    private Text mkey=new Text();
    private Text mvalue=new Text();
    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        System.out.println("map");
        //lines1:    A       B,C,D,F,E,O
        String[] lines1 = value.toString().split(":");
        //lines2:    B C D F E O
        String[] lines2 = lines1[1].split(",");
        for (String word:lines2){
            //将好友拆分后依次写入map输出key
            mkey.set(word);
            //map输出value始终为该好友所属用户
            mvalue.set(lines1[0]);
            context.write(mkey,mvalue);
        }
    }
}

3. reduce

static class FriendReduceer extends Reducer<Text,Text,Text,Text>{
    private Text rkey=new Text();
    private Text rvalue=new Text();
    @Override
    protected void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException {
        System.out.println("reduce");
        //创建ArrayList用于装map输出value,便于索引
        List<String> slist=new ArrayList<>();
        for (Text v:values){
            slist.add(v.toString());
        }
        //排序,保证A-Z的顺序
        Collections.sort(slist);
        //reduce会将同一个好友的拥有者放入一个reduce,通过for循环遍历两两组合
        for (int i=0;i<slist.size()-1;i++){
            for (int j=0;j<slist.size()-1;j++){
                //过滤掉重复的用户组合
                if (j<=i){
                    continue;
                }
                //输出格式为用户-用户 好友
                String tmpkey=slist.get(i)+"-"+slist.get(j);
                rkey.set(tmpkey);
                rvalue.set(key.toString());
                context.write(rkey,rvalue);
            }
        }
    }
}

4. 第二次mapreduce, 实现合并两个用户的共同好友

主方法不变, 只列出map和reduce类,将第一次mapreduce输出文件作为输入文件

static class FriendMaper extends Mapper<LongWritable,Text,Text,Text>{
    private Text mkey=new Text();
    private Text mvalue=new Text();
    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        System.out.println("map");
        //lines: B-C    A
        String[] lines = value.toString().split("\\s");
        mvalue.set(lines[1]);
        mkey.set(lines[0]);
        //map输出key为用户-用户,输出value为其共同好友
        context.write(mkey,mvalue);
    }
}
static class FriendReduceer extends Reducer<Text,Text,Text,Text> {
    private Text rvalue=new Text();
    @Override
    protected void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException {
        System.out.println("reduce");
        //StringBuffer 可以追加字符串
        StringBuffer buf=new StringBuffer();
        for (Text v:values){
            buf.append(v.toString()+" ");
        }
        rvalue.set(buf.toString());
        context.write(key,rvalue);
    }
}