Hadoop(11)-MapReduce概述和简单实操

1.MapReduce的定义

2.MapReduce的优缺点

优点

缺点

3.MapReduce的核心思想

4.MapReduce进程

5.常用数据序列化类型

6.MapReduce的编程规范

用户编写的程序分成三个部分：Mapper、Reducer和Driver

7.WordCount简单操作

需求:在给定的文本文件中统计输出每一个单词出现的总次数

如一个类似这样的文件

Mapper类

package com.nty.wordcount;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

import java.io.IOException;

/**
 * author nty
 * date time 2018-12-07 16:33
 */
//Mapper<KEYIN, VALUEIN, KEYOUT, VALUEOUT> 四个泛型分别表示,输入Key类型,输入Value类型,输出Key类型,输出Value类型
public class WcMapper extends Mapper<LongWritable, Text, Text, IntWritable> {
    //定义成员变量,节省堆内存
    private Text key = new Text();
    private IntWritable value = new IntWritable(1);

    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        
        String[] words = value.toString().split(" ");

        for (String word : words) {
            this.key.set(word);
            context.write(this.key,this.value);

        }
    }
}

 Reducer类

package com.nty.wordcount;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

import java.io.IOException;

/**
 * author nty
 * date time 2018-12-07 16:34
 */
//Reducer<KEYIN,VALUEIN,KEYOUT,VALUEOUT> 四个泛型分别为,输入Key类型,输入Value类型,输出Key类型,输出Value类型
public class WcReducer extends Reducer<Text, IntWritable, Text, IntWritable> {

    private int sum;

    private IntWritable total = new IntWritable();

    @Override
    protected void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
        sum = 0;

        for (IntWritable value : values) {
            sum += value.get();
        }
        this.total.set(sum);
        context.write(key, this.total);

    }
}

Driver类

package com.nty.wordcount;

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

/**
 * author nty
 * date time 2018-12-07 16:35
 */
public class WcDriver {

    public static void main(String[] args) throws Exception {
        //1.获取配置信息和任务
        Configuration configuration = new Configuration();
        Job job = Job.getInstance(configuration);
        //2.设置加载路径
        job.setJarByClass(WcDriver.class);
        //3.设置Mapper和Reducer
        job.setMapperClass(WcMapper.class);
        job.setReducerClass(WcReducer.class);
        //4.设置map和reduce的输入输出类型
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(IntWritable.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
        //5.设置输入和输出路径
        FileInputFormat.setInputPaths(job,new Path(args[0]));
        FileOutputFormat.setOutputPath(job,new Path(args[1]));
        //6 提交
        boolean b = job.waitForCompletion(true);
        System.exit(b ? 0 : 1);
    }


}

main方法的args

输出结果