Hadoop实战：reduce端实现Join

项目描述

        现在假设有两个数据集：气象站数据库和天气记录数据库，并考虑如何合二为一。一个典型的查询是：输出气象站的历史信息，同时各行记录也包含气象站的元数据信息。

       气象站和天气记录合并之后的示意图如下所示。

测试数据

       启动Hadoop集群，然后在hdfs中创建join文件夹用于存放测试数据station.txt和records.txt，他们分别代表气象站数据库和天气记录数据库。

项目代码

JoinStationMapper.java

package com.hadoop.Join;

import java.io.IOException;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

/**
 * @author Zimo
 *
 */
public class JoinStationMapper extends Mapper<LongWritable,Text,TextPair,Text>
{  
    protected void map(LongWritable key,Text value,Context context) throws IOException,InterruptedException
    {
        String line = value.toString();
        String[] arr = line.split("\\s+");//解析气象站数据
        int length = arr.length;
        if(length==2)
        {//满足这种数据格式
            //key=气象站id  value=气象站名称
            System.out.println("station="+arr[0]+"0");
            context.write(new TextPair(arr[0],"0"),new Text(arr[1]));
        }
    }
}

 

JoinRecordMapper.java

package com.hadoop.Join;

import java.io.IOException;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

/**
 * @author Zimo
 *
 */
public class JoinRecordMapper extends Mapper<LongWritable,Text,TextPair,Text>
{ 
    protected void map(LongWritable key,Text value,Context context) throws IOException,InterruptedException
    {
        String line = value.toString();
        String[] arr = line.split("\\s+",2);//解析天气记录数据
        int length = arr.length;
        if(length==2){
            //key=气象站id  value=天气记录数据
            context.write(new TextPair(arr[0],"1"),new Text(arr[1]));
        }  
    }
}

 

TextPair.java

package com.hadoop.Join;

import java.io.*;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.WritableComparable;

/**
 * @author Zimo
 *
 */
public class TextPair  implements WritableComparable<TextPair>
{
	private Text first; //Text 类型的实例变量first
	private Text second;//Text 类型的实例变量second
	
	public TextPair() //无参构造方法
	{
		set(new Text(),new Text());
	}
	public TextPair(String first,String second)  // Sting类型参数的构造方法
	{
		set(new Text(first),new Text(second));
	}
	public TextPair(Text first,Text second)  // Text类型参数的构造方法
	{
		set(first,second);
	}
	public void set(Text first,Text second) //set方法
	{
		this.first=first;
		this.second=second;
	}
	public Text getFirst() //getFirst方法
	{
		return first;
	}
	public Text getSecond() //getSecond方法
	{
		return second;
	}
	
	//将对象转换为字节流并写入到输出流out中
	@Override    //------------ 序列化 
	public void write(DataOutput out) throws IOException //write方法
	{
		first.write(out);
		second.write(out);
	}
	
	//从输入流in中读取字节流反序列化为对象
	@Override   //------------反 序列化 
	public void readFields(DataInput in) throws IOException //readFields方法
	{
		first.readFields(in);
		second.readFields(in);
	}
	
	@Override
	public int hashCode() //在mapreduce中，通过hashCode来选择reduce分区
	{
		return first.hashCode() *163+second.hashCode();
	}
	
	@Override
	public boolean equals(Object o) //equals方法，这里是两个对象的内容之间比较
	{
		if (o instanceof TextPair)
		{
			TextPair tp=(TextPair) o;
			return first.equals(tp.first) && second.equals(tp.second);
		}
		return false;
	}
	
	@Override
	public String toString() //toString方法
	{
		return first +"\t"+ second;
	}
	@Override
	public int compareTo(TextPair o)
	{
		// TODO Auto-generated method stub
		if(!first.equals(o.first))
		{
			return first.compareTo(o.first);
		}
		else if(!second.equals(o.second))
		{
			return second.compareTo(o.second);
		}
		return 0;
	}
	

}

JoinReducer.java

package com.hadoop.Join;

import java.io.IOException;

import java.util.Iterator;

import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

/**
 * @author Zimo
 *
 */
public class JoinReducer extends Reducer< TextPair,Text,Text,Text>
{
    protected void reduce(TextPair key, Iterable< Text> values,Context context) throws IOException,InterruptedException
    {
        Iterator< Text> iter = values.iterator();
        Text stationName = new Text(iter.next());//气象站名称
        while(iter.hasNext()){
            Text record = iter.next();//天气记录的每条数据
            Text outValue = new Text(stationName.toString()+"\t"+record.toString());
            context.write(key.getFirst(),outValue);
        }
    }        
}

 

JoinRecordWithStationName.java

package com.hadoop.Join;

import java.io.InputStream;
import org.apache.hadoop.util.Tool;
import java.io.OutputStream;
import java.util.Set;

import javax.lang.model.SourceVersion;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.io.WritableComparator;

import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Partitioner;
import org.apache.hadoop.mapreduce.lib.input.MultipleInputs;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.ToolRunner;

/**
 * @author Zimo
 *
 */
public class JoinRecordWithStationName extends Configured implements Tool
{
    public static class KeyPartitioner extends Partitioner< TextPair,Text>
    {
        
        public int getPartition(TextPair key,Text value,int numPartitions)
        {
            return (key.getFirst().hashCode()&Integer.MAX_VALUE) % numPartitions;
        }
    }
    
    public static class GroupingComparator extends WritableComparator
    {
        protected GroupingComparator()
        {
            super(TextPair.class,true);
        }
        @Override
        public int compare(WritableComparable w1,WritableComparable w2)
        {
            TextPair ip1=(TextPair) w1;
            TextPair ip2=(TextPair) w2;
            Text l=ip1.getFirst();
            Text r=ip2.getFirst();
            return l.compareTo(r);
        
        } 
    }
    public int run(String[] args) throws Exception
    {
        Configuration conf = new Configuration();// 读取配置文件
        
        Path mypath=new Path(args[2]);
        FileSystem hdfs=mypath.getFileSystem(conf);
        if (hdfs.isDirectory(mypath))
        {
            hdfs.delete(mypath,true);
        }
        
        Job job = Job.getInstance(conf,"join");// 新建一个任务
        job.setJarByClass(JoinRecordWithStationName.class);// 主类
        
        Path recordInputPath = new Path(args[0]);//天气记录数据源，这里是牵扯到多路径输入和多路径输出的问题。默认是从args[0]开始
        Path stationInputPath = new Path(args[1]);//气象站数据源
        Path outputPath = new Path(args[2]);//输出路径
        
        //若只有一个输入和一个输出，则输入是args[0]，输出是args[1]。
        //若有两个输入和一个输出，则输入是args[0]和args[1]，输出是args[2]
        
        MultipleInputs.addInputPath(job,recordInputPath,TextInputFormat.class,JoinRecordMapper.class);//读取天气记录Mapper
        MultipleInputs.addInputPath(job,stationInputPath,TextInputFormat.class,JoinStationMapper.class);//读取气象站Mapper
        FileOutputFormat.setOutputPath(job,outputPath);
        job.setReducerClass(JoinReducer.class);// Reducer
        job.setNumReduceTasks(2);
        
        job.setPartitionerClass(KeyPartitioner.class);//自定义分区
        job.setGroupingComparatorClass(GroupingComparator.class);//自定义分组
        
        job.setMapOutputKeyClass(TextPair.class);
        job.setMapOutputValueClass(Text.class);
    
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(Text.class);
        
        return job.waitForCompletion(true)?0:1;
    }
        
        public static void main(String[] args) throws Exception
        {
            String[] args0={"hdfs://centpy:9000/join/records.txt"
                            ,"hdfs://centpy:9000/join/station.txt"
                            ,"hdfs://centpy:9000/join/out"
            };
            int exitCode=ToolRunner.run( new JoinRecordWithStationName(), args0);
            System.exit(exitCode);
        }
}

 

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