MapReduce编程实例

MapReduce编程实例（六）

前提准备：

1.hadoop安装运行正常。Hadoop安装配置请参考：Ubuntu下 Hadoop 1.2.1 配置安装

2.集成开发环境正常。集成开发环境配置请参考 ：Ubuntu 搭建Hadoop源码阅读环境

MapReduce编程实例：

MapReduce编程实例（一）,详细介绍在集成环境中运行第一个MapReduce程序 WordCount及代码分析

MapReduce编程实例（二），计算学生平均成绩

MapReduce编程实例（三），数据去重

MapReduce编程实例（四），排序

MapReduce编程实例（五），MapReduce实现单表关联

MapReduce编程实例（六），MapReduce实现多表关联

多表关联

描述：

两张表关联，如下：

左表：

factoryname address
BMW Factory 2
Benz Factory 3
Voivo Factory 4
LG Factory 5

右表：

addressID addressname
2 Beijing
3 Guangzhou
4 Shenzhen
5 Sanya

根据addressID关联求出factoryname-address表。很明显，左右关联即可，和单表关联一样。不多作表述，有需要可以查看单表关联的分析。

package com.t.hadoop;

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

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
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;
import org.apache.hadoop.util.GenericOptionsParser;

/**
 * 多表排序
 * @author daT [email protected]
 *
 */
public class MTJoin {
    public static int times = 1;

    public static class MTMapper extends Mapper<Object, Text, Text, Text>{

        @Override
        protected void map(Object key, Text value, Context context)
                throws IOException, InterruptedException {
            String relation = new String();
            String line = value.toString();
            if(line.contains("factoryname")||line.contains("addressID")) return;
            int i = 0;
            while(line.charAt(i)<'0'||line.charAt(i)>'9'){
                i++;
            }
            if(i>0){//左表
                relation = "1";
                context.write(new Text(String.valueOf(line.charAt(i))),new Text(relation + line.substring(0,i-1)));
            }else{//右表
                relation = "2";
                context.write(new Text(String.valueOf(line.charAt(i))),new Text(relation +line.substring(i+1)));
            }

        }

    }


    public static class MTReducer extends Reducer<Text, Text, Text, Text>{

        @Override
        protected void reduce(Text key, Iterable<Text> value,Context context)
                throws IOException, InterruptedException {
            if(times==1){
                context.write(new Text("factoryName"), new Text("Address"));
                times ++;
            }
            int factoryNum = 0;
            int addressNum = 0;
            String[] factorys = new String[10];
            String[] addresses = new String[10];

            for(Text t:value){
                if(t.charAt(0)=='1'){//左表
                    factorys[factoryNum]=t.toString().substring(1);
                    factoryNum++;
                }else{//右表
                    addresses[addressNum]=t.toString().substring(1);
                    addressNum++;
                }
            }

            for(int i = 0;i<factoryNum;i++){
                for(int j=0;j<addressNum;j++){
                    context.write(new Text(factorys[i]), new Text(addresses[j]));
                }
            }

        }

    }

    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException{
        Configuration conf = new Configuration();
        String[] otherArgs = new GenericOptionsParser(conf,args).getRemainingArgs();

        if(otherArgs.length<2){
            System.out.println("Parameters error");
            System.exit(2);
        }

        Job job =new Job(conf,"MTjoin");
        job.setJarByClass(MTJoin.class);
        job.setMapperClass(MTMapper.class);
        job.setReducerClass(MTReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(Text.class);

        FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
        FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));

        System.exit(job.waitForCompletion(true)?0:1);

    }
}

输出结果：

factoryName Address
BMW Factory Beijing
Benz Factory Guangzhou
Voivo Factory Shenzhen
LG Factory Sanya