WordCount

1.　　一个mapper

package MapReduce;




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

import java.io.IOException;

/**
 * @Author:Dapeng
 * @Discription:    默认的MapReduce是通过TextInputFormat进行切片，并交给Mapper处理
 *                  TextInputFormat：key:当前行的首字母的索引，value：当前行里面放了什么数据
 * @Date:Created in 下午 15:00 2018/10/25 0025
 */
public class MyMapper extends Mapper<LongWritable,Text,Text,LongWritable> {
    LongWritable one = new LongWritable(1);
    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        //第一个key代表第几行
        //第一个value表示某一行的内容

        //将一行Text转换为String
        String words = value.toString();

        //将一行words切片成为单词
        String[] wordArr = words.split(" ");

        //遍历每个单词
        for(String str:wordArr){
            context.write(new Text(str),one);
        }

    }
}

2.　　一个reducer

package MapReduce;


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

import java.io.IOException;

/**
 * @Author:Dapeng
 * @Discription:
 * @Date:Created in 下午 15:16 2018/10/25 0025
 */
public class MyReducer extends Reducer<Text,LongWritable,Text,LongWritable> {
    @Override
    protected void reduce(Text key, Iterable<LongWritable> values, Context context) throws IOException, InterruptedException {
        Long sum = 0L;
        for(LongWritable value:values){
            sum += value.get();
        }
        context.write(key,new LongWritable(sum));
    }
}

3.　　一个Job

package MapReduce;


import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
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;

/**
 * @Author:Dapeng
 * @Discription:
 * @Date:Created in 下午 14:50 2018/10/25 0025
 */
public class WordCount {
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {

        //0.创建一个job
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf,"word_count");
        job.setJarByClass(WordCount.class);
        //1.输入文件
        //默认用TextInputFormat
        FileInputFormat.addInputPath(job,new Path(args[0]));
        //2.编写mapper
        job.setMapperClass(MyMapper.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(LongWritable.class);
        //3.shuffle

        //4.reduce
        job.setReducerClass(MyReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(LongWritable.class);
        //5.输出
        FileOutputFormat.setOutputPath(job,new Path(args[1]));

        //6.运行
        boolean result = job.waitForCompletion(true);
        System.out.println(result);
    }
}

4.　　打包

https://www.cnblogs.com/blog5277/p/5920560.html

5.　　运行命令

yarn　jar　 Myhadoop.jar 　　mapreduce.WordCount 　　/user/out.txt　　/user/myout 　　(最后一个是输出的文件夹）

　　　　jar包名字　　　　主类　　　　　　　　　　　　参数1　　　　参数2

6.　　结果查看

生成一个part-r-00000文件，存放结果

查看结果