MapReduce寻找共同好友

1.测试文件

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

2.方法

2-1.方法一：

1.将域用户和好友分别作为值和键输出  {B,C,D,F,E,O}:A  {A,C,E,K}:B2.可以看出：B,C,D,F,E,O都有共同好友A，3.把A的好友两两组合作为键，A作为值，冒泡输出4.经过shuffle处理后，会把BC作为键，共同好友作为值放入集合中5.迭代集合中的好友，一次输出即可

2-2.方法二：

1.将用户和好友作为键和值输出  A:B,C,D,F,E,O     --A:B,C,D,F,E,O  B:A,C,E,K     --B:A,C,E,K  C:F,A,D,I     --C:A,D,F,I  D:A,E,F,L     --D:A,E,F,L  E:B,C,D,M,L       --E:B,C,D,L,M2.将所有键值对添加到map集合中3.取map的键（所有用户）为数组4.迭代数组，通过用户名"A"在map中取得他的好友5.迭代除用户"A"以外的其他用户，获取这些用户的好友；  如果有用户同时存在于"A"和"B"的好友列表中  那么这些好友就是"AB"的共同好友  --A:{B,C,D,F,E,O}  --B:{A,C,E,K}  "A"中存在"C,E"用户，"B"中也存在"C,E"用户，那么"C,E"就是AB的共同好友6.将"AB"作为键，共同好友作为值输出即可

3.代码

public class Friends {    // map    public static class MRMapper extends Mapper<LongWritable, Text, Text, Text> {        protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {            String str = value.toString();            String friends = str.substring(2);            System.out.println(friends);            context.write(new Text(str.charAt(0) + ""), new Text(friends));        }    }    // reduce    public static class MRReducer extends Reducer<Text, Text, Text, Text> {        private static HashMap<String, String> map1 = new HashMap<String, String>();        public void run(Context context) throws IOException, InterruptedException {            try {                while (context.nextKeyValue()) {                    reduce(context.getCurrentKey(), context.getValues(), context);                }            } finally {                cleanup(context);            }        }        public void reduce(Text key, Iterable<Text> iterable, Context context)                throws IOException, InterruptedException {            for (Text t : iterable) {                map1.put(key.toString(), t.toString());            }        }        public void cleanup(Reducer<Text, Text, Text, Text>.Context context)                 throws IOException, InterruptedException {            List<String> list = new ArrayList<String>();            Collection<String> keys = map1.keySet();// 所有用户            String keys1 = keys.toString();            String keys2 = keys1.substring(1, keys1.length() - 1);            String[] split = keys2.split(",");            for (int i = 1; i < split.length; i++) {//迭代用户                String a = split[i].trim();                for (int j = (i+1); j < split.length; j++) {//迭代除外层循环以外的用户                    String b = split[j].trim();                    String a_and_b = "";                    // a的好友                    String af = map1.get(a);                    String[] friends = af.split(",");                    for (String s : friends) {//比较两个用户的好友列表，取共同好友                        if (map1.get(b).contains(s)) {                            a_and_b += "," + s;                        }                    }                    System.out.println(a + "," + b + " 共同好友  " + a_and_b);                    if (a_and_b.length() > 1) {                        list.add(a + "," + b + " 共同好友 :" + a_and_b.substring(1));                    }                }            }            for(String s:list){                context.write(new Text(""), new Text(s));            }        }    }    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {        Configuration conf = new Configuration();        Job job = Job.getInstance(conf);        job.setJarByClass(Friends.class);        job.setMapperClass(MRMapper.class);        job.setReducerClass(MRReducer.class);        job.setCombinerClass(MRReducer.class);        job.setMapOutputKeyClass(Text.class);        job.setMapOutputValueClass(Text.class);        job.setOutputKeyClass(Text.class);        job.setOutputValueClass(Text.class);        FileInputFormat.setInputPaths(job, new Path("hdfs://hadoop5:9000/input/friends.txt"));        FileOutputFormat.setOutputPath(job, new Path("hdfs://hadoop5:9000/output/friends"));        System.out.println(job.waitForCompletion(true) ? 1 : 0);    }}

如果有更简洁的方法，欢迎留言给博主。