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MapReduce入门例子之WordCount单词计数



教程目录


  • ​​0x00 教程内容​​
  • ​​0x01 单词计数​​

  • ​​1. 操作流程​​
  • ​​2. 源码​​
  • ​​3. 源码简单解释​​

  • ​​0x02 Web UI界面查看​​
  • ​​1. YARN​​
  • ​​0xFF 总结​​


0x00 教程内容


  1. 单词计数操作流程
  2. 编写MapReduce单词计数代码及简单解释
  3. YARN Web UI界面查看

0x01 单词计数

1. 操作流程

a. 建Maven项目

b. 导入依赖包

PS:a、b两步可参考此文章的​​0x01 新建maven工程​​:​ ​
Java API实现HDFS的相关操作​​

c. 写代码

d. 打包到服务器

e. 准备一份文件,以空格进行分割,放于HDFS上(可自行修改):

​/files/put.txt​

我的数据:

shao nai yi
nai nai yi yi
shao nai nai

f. 启动服务器的HDFS、YARN

g. 执行作业(自行修改):

​hadoop jar hadoop-learning-1.0.jar com.shaonaiyi.hadoop.WordCount hdfs://master:9999/files/put.txt hdfs://master:9999/output/wc/​

2. 源码
package com.shaonaiyi.hadoop;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
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.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;

/**
* @Auther: 邵奈一
* @Date: 2019/03/21 下午 7:02
* @Description: WordCount入门例子之单词计数(Java版)
* 使用脚本:hadoop jar hadoop-learning-1.0.jar com.shaonaiyi.hadoop.WordCount hdfs://master:9999/files/put.txt hdfs://master:9999/output/wc/
*/
public class WordCount {

public static 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 {

String lines = value.toString();
String[] words = lines.split(" ");
for (String word: words){
context.write(new Text(word), one);
}
}

}

public static class MyReducer extends Reducer<Text, LongWritable, Text, LongWritable> {

@Override
protected void reduce(Text key, Iterable<LongWritable> values, Context context) throws IOException, InterruptedException {

int sum = 0;
for (LongWritable value: values){
sum += value.get();
}
context.write(key, new LongWritable(sum));

}
}

public static void main(String[] args) throws Exception{

Configuration configuration = new Configuration();

// 若输出路径有内容,则先删除
Path outputPath = new Path(args[1]);
FileSystem fileSystem = FileSystem.get(configuration);
if(fileSystem.exists(outputPath)){
fileSystem.delete(outputPath, true);
System.out.println("路径存在,但已被删除");
}

Job job = Job.getInstance(configuration, "WordCount");

job.setJarByClass(WordCount.class);

job.setMapperClass(MyMapper.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(LongWritable.class);

job.setReducerClass(MyReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(LongWritable.class);

FileInputFormat.setInputPaths(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));

System.exit(job.waitForCompletion(true) ? 0 : 1);

}

}
3. 源码简单解释

a. 可改切割符,目前为空格:

​String[] words = lines.split(" ");​

b. 分别为第一个参数输入路径​​args[0]​​与第二个参数传出路径​​args[1]​​:

​FileInputFormat.setInputPaths(job, new Path(args[0]));​

​FileOutputFormat.setOutputPath(job, new Path(args[1]));​

0x02 Web UI界面查看

1. YARN

a. 打开UI界面

​​

​​

​​

b. 点击​RUNNING​​、​​FINISHED​​可分别点击查看作业的进度

MapReduce入门例子之WordCount单词计数_apache

0xFF 总结


  1. 不能在本地直接用IDEA执行,要打包然后上传到服务器上
  2. 思考题:请为程序加个足够长的执行时间,然后查看执行作业时,三台服务器上的进程变化。
    思路:在Reduce类添加3秒延迟,在主类设置成2个reduce结果,执行代码时统计多几个文件,用​​*​​号通配,然后一直观察三天服务器的进程,期间也可以查看YARN的Web UI界面上的Map和Reduce有几个。

作者简介:​​邵奈一​​

大学大数据讲师、大学市场洞察者、专栏编辑

公众号、微博​:​​邵奈一​​

​​复制粘贴玩转大数据系列专栏​​已经更新完成,请跳转学习!



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