本文主要向大家介绍了JAVA语言之java map端 实现join代码实例，通过具体的内容向大家展示，希望对大家学习JAVA语言有所帮助。

package cn.smart.bigdata.mr.mapsidejoin;

import java.io.BufferedReader;

import java.io.FileInputStream;

import java.io.IOException;

import java.io.InputStreamReader;

import java.net.URI;

import java.util.HashMap;

import java.util.Map;

import org.apache.commons.lang.StringUtils;

import org.apache.hadoop.conf.Configuration;

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.Job;

import org.apache.hadoop.mapreduce.Mapper;

import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;

import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class MapSideJoin {

    static class MapsideJoinMapper extends Mapper<longwritable, nullwritable="">{

        Map<string, string=""> pdInfoMap = new HashMap<>();

        Text k = new Text();

        @Override

        protected void setup(Mapper<longwritable, nullwritable="">.Context context)

                throws IOException, InterruptedException {

            BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("/D:/data/mapjoincache/pdts.txt")));           

            String line;

            while(StringUtils.isNotBlank(line=br.readLine())){

                String[] fields = line.split(",");

                pdInfoMap.put(fields[0], fields[1]);

            }

            br.close();

        }

        @Override

        protected void map(LongWritable key, Text value, Mapper<longwritable, nullwritable="">.Context context)

                throws IOException, InterruptedException {

            String orderLine = value.toString();

            String[] fields = orderLine.split("\t");

            String pdName = pdInfoMap.get(fields[1]);

            k.set(orderLine + "\t" + pdName);

            context.write(k, NullWritable.get());

        }

    }

    public static void main(String[] args) throws Exception {

        Configuration conf = new Configuration();

        Job job = Job.getInstance(conf);

        job.setJarByClass(MapSideJoin.class);

        job.setMapperClass(MapsideJoinMapper.class);

        job.setOutputKeyClass(Text.class);

        job.setOutputValueClass(NullWritable.class);

        FileInputFormat.setInputPaths(job, new Path("D:/data/mapjoininput"));

        FileOutputFormat.setOutputPath(job, new Path("D:/data/mapjoinoutput"));

        job.addCacheFile(new URI("file:/D:/data/mapjoincache/pdts.txt"));

        job.setNumReduceTasks(0);

        boolean res = job.waitForCompletion(true);

        System.exit(res?1:0);

    }

}

pdts.txt

pd001,apple

pd002,banana

pd003,orange

order.txt

1001 pd001 300

1001 pd002 20

1002 pd003 40

1003 pd002 50

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