Hadoop 自连接

环境：CentOS6.6  Hadoop1.2.1

样例数据：第一列是 child ，第二列是 parent ，用空格分开，要求输出 grandchild  grandparent

[grid@hadoop1 ~]$ hadoop fs -cat ./in/genealogy.txt
Tom Lucy
Tom Jack
Jone Lucy
Jone Jack
Lucy Mary
Lucy Ben
Jack Alice
Jack Jesse
Terry Alice
Terry Jesse
Philip Terry
Philip Alma
Mark Terry
Mark Alma

程序：

import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import java.io.IOException;
public class SelfJoinMapper extends Mapper<Text, Text, Text, Text> {
    @Override
    protected void map(Text key, Text value, Context context) throws IOException, InterruptedException {
        context.write(value, new Text("1" + key.toString())); //左表的 parent 做 key
        context.write(key, new Text("2" + value.toString())); //右表的 child 做 key
    }
}

import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
public class SelfJoinReducer extends Reducer<Text, Text, Text, Text> {
    @Override
    protected void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException {
        List<String> childList = new ArrayList<String>();
        List<String> grandList = new ArrayList<String>();
        for (Text value : values) {
            if (value.toString().startsWith("1")) {
                childList.add(value.toString().substring(1));
            } else {
                grandList.add(value.toString().substring(1));
            }
        }
        for (String child : childList) {
            for (String grand : grandList) {
                context.write(new Text(child), new Text(grand));
            }
        }
    }
}

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.input.KeyValueTextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
public class SelfJoin {
    public static void main(String[] args) throws Exception {
        if (args.length != 2) {
            System.err.println("Usage: SelfJoin <input path> <output path>");
            System.exit(-1);
        }

        Configuration conf = new Configuration();
        conf.set("mapreduce.input.keyvaluelinerecordreader.key.value.separator", " "); //设置分割符
        //conf.set("mapred.jar", "./out/SelfJoin.jar");
        //conf.set("fs.default.name", "hdfs://hadoop1:9000");
        //conf.set("mapred.job.tracker", "hadoop1:9001");

        Job job = new Job(conf);
        job.setInputFormatClass(KeyValueTextInputFormat.class); //设置 InputFormat
        job.setJarByClass(SelfJoin.class);
        job.setJobName("SelfJoin");
        FileInputFormat.addInputPath(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));
        job.setMapperClass(SelfJoinMapper.class);
        job.setReducerClass(SelfJoinReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(Text.class);
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
}

查看程序输出如下：

[grid@hadoop1 ~]$ hadoop fs -cat ./out/9/part-r-00000
Tom	Alice
Tom	Jesse
Jone	Alice
Jone	Jesse
Tom	Mary
Tom	Ben
Jone	Mary
Jone	Ben
Philip	Alice
Philip	Jesse
Mark	Alice
Mark	Jesse