Hadoop MapReduce 在某一列上自连接(self join)

package mapreduce;

import java.util.List;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;

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.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 Self_join {
public static class Map extends Mapper<Object, Text, Text, Text>{
public void map(Object key,Text value, Context context) throws IOException,InterruptedException{
String line = value.toString();
String[] ss = line.split(" ", 2);
context.write(new Text(ss[1]), new Text("left_"+ss[0]));
context.write(new Text(ss[0]), new Text("right_"+ss[1]));
}
}

public static class Reduce extends Reducer<Text, Text, Text, Text>{
private static int time =0;
private static List<String> ch = new ArrayList<String>();
private static List<String> g = new ArrayList<String>();

public void reduce(Text key,Iterable<Text> values,Context context) throws IOException,InterruptedException{
if(time == 0){
context.write(new Text("grandchild"), new Text("grandparent"));
time ++;
}
Iterator<Text> ite = values.iterator();
ch.clear();
g.clear();
while(ite.hasNext()){
String p = ite.next().toString();
if(p.startsWith("left_")){
ch.add(p.replaceFirst("^left_", ""));
}
if(p.startsWith("right_")){
g.add(p.replaceFirst("^right_", ""));
}
}
Iterator<String> chi = ch.iterator();
Iterator<String> gi = g.iterator();

while(chi.hasNext()){
String c = chi.next();
while(gi.hasNext()){
context.write(new Text(c), new Text(gi.next()));
}
}
}
}

public static void main(String[] args) throws Exception{
Configuration conf = new Configuration();
Job job = Job.getInstance(conf, "Selfjoin");
job.setJarByClass(Self_join.class);
job.setMapperClass(Map.class);
job.setReducerClass(Reduce.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);
FileInputFormat.addInputPath(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
System.exit(job.waitForCompletion(true) ? 0 : 1);
}

}