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{

		@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{

		@Override
		protected void reduce(Text key, Iterable 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





输出结果：

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

欢迎同学们多多交流～