一、需求分析

1、文件

hadoop is ok
hadoop not ok
java is fun
php is ok
php is pretty
python is all
go is new

2、需求

对上述文件中每个单词出现的数量进行统计，2行数据一个切片

3、分析

与传统的WordCount相似，但是按行切片，而不是BlockSize

二、代码

前提条件：创建Maven项目，导入依赖，配置log日志

1、Mapper

package com.ln;

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;

public class LNMapper extends Mapper<LongWritable, Text, Text, IntWritable> {
    Text k = new Text();
    IntWritable v = new IntWritable(1);
    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        // 1.获取行
        String line = value.toString();
        // 2.切割
        String[] words = line.split("\\s+");
        // 3.循环写入
        for (String word : words) {
            k.set(word);
            context.write(k, v);
        }
    }
}

2、Reducer

package com.ln;

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

import java.io.IOException;

public class LNReducer extends Reducer<Text, IntWritable,Text,IntWritable> {
    IntWritable v = new IntWritable();
    @Override
    protected void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
        // 1.累加
        int sum =  0;
        for (IntWritable value : values) {
            sum += value.get();
        }
        // 2. 写入
        v.set(sum);
        context.write(key, v);
    }
}

3、Driver

package com.ln;

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

import java.io.IOException;

public class LNDriver {
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
        args = new String[]{"E:\\a\\input", "E:\\a\\output"};
        // 1. 获取job
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf);
        // 2. 设置Jar
        job.setJarByClass(LNDriver.class);
        // 3. 关联 mapper 和 reducer
        job.setMapperClass(LNMapper.class);
        job.setReducerClass(LNReducer.class);
        // 4. 设置 mapper的输出  kv
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(IntWritable.class);
        // 5. 设置 最终 输出 kv
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
        // a. 设置 每个切片中 2 调记录
        NLineInputFormat.setNumLinesPerSplit(job, 2);
        // b、设置 inputFormat 的 格式
        job.setInputFormatClass(NLineInputFormat.class);
        // 6. 设置 输入 输出路径
        FileInputFormat.setInputPaths(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));
        // 7. 提交 job
        boolean wait = job.waitForCompletion(true);
        System.exit(wait? 0: 1);
    }
}

注意：

核心代码

1、设置一个切片有多少行数据

NLineInputFormat.setNumLinesPerSplit(job, 2);

2、设置InputFormat的格式

job.setInputFormatClass(NLineInputFormat.class);

结果：

运行完成后：

number of splits:4

 

版权声明：本文为wt7018原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接和本声明。
本文链接：https://www.cnblogs.com/wt7018/p/13612760.html