商品的平均点击次数

求商品的平均点击次数，也就是求平均数，因此根据MapReduce的流程，在Mapper中将数据转换为键值对形式，再经过shuffle，然后将键值对交到reducer，在此处对商品点击次数进行求平均值并输出
代码 实现：

package com.ks.clickCount;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
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 java.io.IOException;
import java.util.Iterator;
import java.util.StringTokenizer;

class CCMapper extends Mapper<LongWritable, Text, Text, IntWritable> {
    
    
    private static Text goods = new Text();
    @Override
    protected void map(LongWritable key, Text value,Context context)
            throws IOException, InterruptedException {
    
    
        String val = value.toString();  //text类型转为string类型
        String arr[] = val.split("\t");
        goods.set(arr[0]);
        int click = Integer.parseInt(arr[1]);
        context.write(goods,new IntWritable(click));

    }
}

class CCReducer extends Reducer<Text, IntWritable, Text, IntWritable> {
    
    
    @Override
    protected void reduce(Text key, Iterable<IntWritable> values,Context context)
            throws IOException, InterruptedException {
    
    
        Iterator<IntWritable> iterator = values.iterator();
        //点击次数分组求和，以及求和次数，以便计算平均数
        int count = 0;
        int sum =0;
        while(iterator.hasNext()){
    
    
            int v = iterator.next().get();
            sum += v;
            count++;
        }
        int avg = sum/count;
        context.write(key, new IntWritable(avg));
    }
}

public class ClickCountMR {
    
    

    public static void main(String[] args) throws Exception {
    
    
        //使用默认的配置类
        Configuration conf = new Configuration();
        //conf.set("fs.defaultFS","hdfs://hdoop01:9000");
        // 创建一个Job
        Job job = Job.getInstance(conf);
        // 设置Job对应的参数: 主类
        job.setJarByClass(ClickCountMR.class);
        // 设置Job对应的参数: 设置自定义的Mapper和Reducer处理类
        job.setMapperClass(CCMapper1.class);
        job.setReducerClass(CCReducer1.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(IntWritable.class);

        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(LongWritable.class);
        job.setNumReduceTasks(1);
        // 设置Job对应的参数: Mapper输出key和value的类型：作业输入和输出的路径
        FileInputFormat.setInputPaths(job,args[0]);
        Path outputPath = new Path(args[1]);

        FileSystem fs = FileSystem.get(conf);
        if(fs.exists(outputPath)){
    
    
            fs.delete(outputPath,false);
        }

        FileOutputFormat.setOutputPath(job,outputPath);
        // 提交job
        boolean isDone = job.waitForCompletion(true);


        //成功后退出
        System.exit(isDone ? 0 : -1);

    }

}
mpletion(true);


        //成功后退出
        System.exit(isDone ? 0 : -1);

    }

}