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,K
以上是数据：
A:B,C,D,F,E,O
表示：B,C,D,E,F,O是A用户的好友。
1、求所有两两用户之间的共同好友
/** * @author: lpj * @date: 2018年3月16日 下午7:16:47 * @Description: */ package lpj.reduceWork; import java.io.IOException; import java.util.Arrays; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.fs.FileSystem; import org.apache.hadoop.fs.Path; import org.apache.hadoop.io.IntWritable; 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.jobcontrol.ControlledJob; import org.apache.hadoop.mapreduce.lib.jobcontrol.JobControl; import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat; /** * */ public class SameFriendsMR { public static void main(String[] args) throws Exception { Configuration conf = new Configuration(); // conf.addResource("hdfs-site.xml");//使用配置文件 // System.setProperty("HADOOP_USER_NAME", "hadoop");//使用集群 ///////////////////第一步//////////////////////// FileSystem fs = FileSystem.get(conf);//默认使用本地 Job job = Job.getInstance(conf); job.setJarByClass(SameFriendsMR.class); job.setMapperClass(SameFriendsMR_Mapper.class); job.setReducerClass(SameFriendsMR_Reducer.class); job.setMapOutputKeyClass(Text.class); job.setMapOutputValueClass(Text.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(Text.class); Path inputPath = new Path("d:/a/homework4.txt"); Path outputPath = new Path("d:/a/homework4"); if (fs.exists(inputPath)) { fs.delete(outputPath, true); } FileInputFormat.setInputPaths(job, inputPath); FileOutputFormat.setOutputPath(job, outputPath); ////////////////////第二步////////////////////////////////// FileSystem fs2 = FileSystem.get(conf);//默认使用本地 Job job2 = Job.getInstance(conf); job2.setJarByClass(SameFriendsMR.class); job2.setMapperClass(SameFriends2MR_Mapper.class); job2.setReducerClass(SameFriends2MR_Reducer.class); job2.setMapOutputKeyClass(Text.class); job2.setMapOutputValueClass(Text.class); job2.setOutputKeyClass(Text.class); job2.setOutputValueClass(Text.class); Path inputPath2 = new Path("d:/a/homework4"); Path outputPath2 = new Path("d:/a/homework4_1"); if (fs2.exists(inputPath2)) { fs2.delete(outputPath2, true); } FileInputFormat.setInputPaths(job2, inputPath2); FileOutputFormat.setOutputPath(job2, outputPath2); //采用jobcontrol进行2个MapReduce串行 ControlledJob aJob = new ControlledJob(job.getConfiguration()); ControlledJob bJob = new ControlledJob(job2.getConfiguration()); aJob.setJob(job); bJob.setJob(job2); bJob.addDependingJob(aJob);//指定依赖关系 JobControl jc = new JobControl("jcF"); jc.addJob(aJob); jc.addJob(bJob); Thread thread = new Thread(jc); thread.start(); while(!jc.allFinished()){ thread.sleep(1000); } jc.stop(); } ///////////////////////////////第一步///////////////////////////////////////// public static class SameFriendsMR_Mapper extends Mapper<LongWritable, Text, Text, Text>{ Text kout = new Text(); Text valueout = new Text(); @Override protected void map(LongWritable key, Text value,Context context)throws IOException, InterruptedException { //A:B,C,D,F,E,O String [] reads = value.toString().trim().split(":"); //以用户为value值，好友为key值，求取以某用户为共同好友的人 String vv = reads[0]; valueout.set(vv); String [] friends = reads[1].split(","); for(int i = 0; i < friends.length; i++){ String kk = friends[i]; kout.set(kk); context.write(kout, valueout); } } } public static class SameFriendsMR_Reducer extends Reducer<Text, Text, Text, Text>{ Text kout = new Text(); Text valueout = new Text(); @Override protected void reduce(Text key, Iterable<Text> values, Context context)throws IOException, InterruptedException { //将用户共同好友的人组合起来 StringBuilder sb = new StringBuilder(); for(Text text : values){ sb.append(text.toString()).append(","); } String vv = sb.substring(0, sb.length() - 1); valueout.set(vv); context.write(key, valueout); } } //////////////////////////////////////第二步/////////////////////////////////////////////////////////// public static class SameFriends2MR_Mapper extends Mapper<LongWritable, Text, Text, Text>{ Text kout = new Text(); Text valueout = new Text(); @Override protected void map(LongWritable key, Text value,Context context)throws IOException, InterruptedException { //A F,I,O,K,G,D,C,H,B ：意思是F,I,O,K,G,D,C,H,B的共同好友为A,第二步执行求取两两好友,A为value，两两对为key String [] reads = value.toString().trim().split("\t"); //A为value String vv = reads[0]; valueout.set(vv); //求两两好友对，为了防止重复，需要对好友进行排序 String [] friends = reads[1].split(","); Arrays.sort(friends); //使用两重循环，寻找A-B等好友对组合 for(int i = 0; i < friends.length - 1; i++){ for(int j = i + 1; j < friends.length; j++ ){ String kk = friends[i] + "-" + friends[j]; kout.set(kk); context.write(kout, valueout); } } } } public static class SameFriends2MR_Reducer extends Reducer<Text, Text, Text, Text>{ Text kout = new Text(); Text valueout = new Text(); @Override protected void reduce(Text key, Iterable<Text> values, Context context)throws IOException, InterruptedException { //好友对组合起来 StringBuilder sb = new StringBuilder(); for(Text text : values){ sb.append(text.toString()).append(","); } String vv = sb.substring(0, sb.length() - 1); valueout.set(vv); context.write(key, valueout); } } }