1.通过缓存实现map端的left join

缓存文件pdts.txt内容：

orders.txt文件内容

1.1）在驱动程序中增加指定文件缓存：

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.filecache.DistributedCache;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

import java.net.URI;

public class MapSideJoin extends Configured implements Tool {
    @Override
    public int run(String[] args) throws Exception {
        Configuration conf = super.getConf();
        //注意，这里的缓存文件的添加，只能将缓存文件放到hdfs文件系统当中，放到本地加载不到，pdts.txt在hdfs文件系统上
        DistributedCache.addCacheFile(new URI("hdfs://node01:8020/mr/cachefile/pdts.txt"),conf);
        Job job = Job.getInstance(conf, MapSideJoin.class.getSimpleName());
        job.setJarByClass(MapSideJoin.class);
        job.setInputFormatClass(TextInputFormat.class);
        TextInputFormat.addInputPath(job,new Path("file:///E:\\input\\orders.txt"));
        job.setMapperClass(JoinMap.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(Text.class);
        job.setOutputFormatClass(TextOutputFormat.class);
        TextOutputFormat.setOutputPath(job,new Path("file:///E:\\cacheout1"));
        boolean b = job.waitForCompletion(true);
        return b?0:1;
    }
    public static void main(String[] args) throws Exception {
        Configuration configuration = new Configuration();
        int run = ToolRunner.run(configuration, new MapSideJoin(), args);
        System.exit(run);
    }
}

1.2）在自定义Map中通过上下文对象获取缓存文件

import org.apache.hadoop.filecache.DistributedCache;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.LongWritable;
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.net.URI;
import java.util.HashMap;

/**
 * map端c操作商品缓存数据
 */
public class JoinMap extends Mapper<LongWritable,Text,Text,Text> {
    HashMap<String,String> b_tab = new HashMap<String, String>();
    String line = null;
    /**
     *  map端的初始化方法，从中可以获取我们的缓存文件，一次性加载到map当中来
     * 使用缓存类DistributedCache.getLocalCacheFiles方法从context上下文中获取缓存数据
     */
    @Override
    public void setup(Context context) throws IOException, InterruptedException {
        //这种方式获取所有的缓存文件
        URI[] cacheFiles = DistributedCache.getCacheFiles(context.getConfiguration());
        //获取到缓存文件路径
        Path[] localCacheFiles = DistributedCache.getLocalCacheFiles(context.getConfiguration());
        //根据URI得到hdfs文件系统，从而拿到缓存文件
        FileSystem fileSystem = FileSystem.get(cacheFiles[0], context.getConfiguration());
        FSDataInputStream open = fileSystem.open(new Path(cacheFiles[0]));
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(open));
        while ((line = bufferedReader.readLine())!=null){
            String[] split = line.split(",");
            b_tab.put(split[0],split[1]+"\t"+split[2]+"\t"+split[3]);
        }
        fileSystem.close();
        IOUtils.closeStream(bufferedReader);
    }

    @Override
    public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        //这里读的是这个map task所负责的那一个切片数据（在hdfs上）
        String[] fields = value.toString().split(",");
        String orderId = fields[0];
        String date = fields[1];
        String pdId = fields[2];
        String amount = fields[3];
        //获取map当中的商品详细信息
        String productInfo = b_tab.get(pdId);
        context.write(new Text(orderId), new Text(date + "\t" + productInfo+"\t"+amount));
    }
}

2）执行方法得到结果文件cacheout1内容