利用mapper实现表的连接

现在有两张表customer和order，需要通过customerid实现customer和order的连接

mapper

package com.cr.JoinMap;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;

public class JoinMapper extends Mapper<LongWritable,Text,Text,NullWritable>{

    //所有的客户信息
     private Map<String,String> allCustomers =  new HashMap<String,String>();

    /**
     * 初始化客户信息（将小表customer存储到mapper里面）
     * @param context 初始化环境变量
     * @throws IOException
     * @throws InterruptedException
     */
    @Override
    protected void setup(Context context) throws IOException, InterruptedException {
        //从上下文获取配置信息
        Configuration conf = context.getConfiguration();
        //从配置信息得到文件系统
        FileSystem fs = FileSystem.get(conf);
        //从文件系统得到输入流
        FSDataInputStream fis = fs.open(new Path("file:///D:/mapjoin/customer.txt"));
        //从输入流阅读器得到缓冲区阅读器
        BufferedReader br = new BufferedReader(new InputStreamReader(fis));
        String line = null;
        while((line = br.readLine()) != null){
            String cid = line.substring(0, line.indexOf(","));
            allCustomers.put(cid,line);

        }
    }

    /**
     * 重写map方法
     * @param key   客户信息
     * @param value 订单信息
     * @param context
     * @throws IOException
     * @throws InterruptedException
     */
    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        String line = value.toString();
        //客户编号
        String cid = line.substring(line.lastIndexOf(",") + 1);
        //订单信息
        String orderInfo = line.substring(0,line.lastIndexOf(","));
        //连接客户信息和订单信息
        String customerInfo = allCustomers.get(cid);
        context.write(new Text(customerInfo + "," + orderInfo),NullWritable.get());
    }
}

app

package com.cr.JoinMap;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.NullWritable;
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.output.FileOutputFormat;

import java.io.IOException;


public class MapJoinOnApp {
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
        //单例作业
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS","file:///");
        System.setProperty("hadoop.home.dir","E:\hadoop-2.7.5");
        Job job = Job.getInstance(conf);

        //设置job的各种属性
        job.setJobName("MapJoinOnApp");                 //设置job名称
        job.setJarByClass(MapJoinOnApp.class);              //设置搜索类

        FileInputFormat.addInputPath(job,new Path(args[0]));

        FileSystem fs = FileSystem.get(conf);

        Path out = new Path(args[1]);
        if(fs.exists(out)){
            fs.delete(out,true);
        }
        FileOutputFormat.setOutputPath(job,new Path(args[1]));

        job.setNumReduceTasks(0);
        job.setMapperClass(JoinMapper.class);

        job.setMapOutputKeyClass(Text.class);            //设置之map输出key
        job.setMapOutputValueClass(NullWritable.class);   //设置map输出value

        job.waitForCompletion(true);
    }
}

结果

注意获取cutomer.txt是直接从mapper的文件系统中获取输入流，而不是从app的参数args里面获取，customer.txt作为小表直接存储在mapper里面，而order.txt作为参数传进去，在mapper里面重写方法map的参数value就是订单信息

参数设置