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HomeDatabaseMysql Tutorial第一个Map/Reduce程序

第一个Map/Reduce程序

Jun 07, 2016 pm 04:31 PM
macmapreducedevelopprogramFirst

当在MAC上搭建好开发环境之后,第一件事肯定是找一个hello world程序练习下。而hadoop世界的hello word程序就是下面的这个Word Count程序。 1. 新建项目 步骤:FileNewOtherMap/Reduce Project 项目名可以随便取,如MapReduceSample。然后新建类WordCount.ja

当在MAC上搭建好开发环境之后,第一件事肯定是找一个hello world程序练习下。而hadoop世界的hello word程序就是下面的这个Word Count程序。

1. 新建项目

步骤:File–>New–>Other–>Map/Reduce Project

项目名可以随便取,如MapReduceSample。然后新建类WordCount.java,其代码如下:

package com.lifeware.test;
import java.io.IOException;
import java.util.*;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.conf.*;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapred.*;
import org.apache.hadoop.util.*;
public class WordCount {

public static class Map extends MapReduceBase implements Mapper {
private final static IntWritable one = new IntWritable(1);
private Text word = new Text();

? ? ? ? public void map(LongWritable key, Text value, OutputCollector output, Reporter reporter) throws IOException {
String line = value.toString();
StringTokenizer tokenizer = new StringTokenizer(line);
while (tokenizer.hasMoreTokens()) {
word.set(tokenizer.nextToken());
output.collect(word, one);
}
}
}

public static class Reduce extends MapReduceBase implements Reducer {
public void reduce(Text key, Iterator values, OutputCollector output, Reporter reporter) throws IOException {
int sum = 0;
while (values.hasNext()) {
sum += values.next().get();
}
output.collect(key, new IntWritable(sum));
}
}
/**
* @param args
* @throws IOException
*/
public static void main(String[] args) throws IOException {
// TODO Auto-generated method stub
JobConf conf = new JobConf(WordCount.class);
conf.setJobName(“wordcount”);

? ?conf.setOutputKeyClass(Text.class);
conf.setOutputValueClass(IntWritable.class);
conf.setMapperClass(Map.class);
conf.setCombinerClass(Reduce.class);
conf.setReducerClass(Reduce.class);

? ?conf.setInputFormat(TextInputFormat.class);
conf.setOutputFormat(TextOutputFormat.class);

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

? ?JobClient.runJob(conf);
}
}

2. 数据准备

为了运行程序,我们分别需要一个输入和输出的文件夹。输出文件夹,在程序运行完成后会自动生成。我们需要给程序传人一个输入文件夹。

2.1. ?准备本地文件

在当前项目目录下新建文件夹input,并在文件夹下新建两个文件file1、file2,这两个文件内容分别如下:

?file1: ? ?Hello World Bye World
file2: ? ? ?Hello Hadoop Goodbye Hadoop

2.2. 将文件夹input上传到分布式文件系统中?

在已经启动Hadoop守护进程终端中cd 到hadoop安装目录,运行下面命令:

bin/hadoop fs -put ../test/input input

将input文件夹上传到了hadoop文件系统后,在该系统下就多了一个input文件夹,你可以使用下面命令查看:

bin/hadoop fs -ls

或者直接通过Eclipse插件,查看DFS Locations显示:

3. 运行项目

3.1. ?在新建的项目MapReduceSample,点击WordCount.java,右键–>Run As–>Run Configurations

3.2. 在弹出的Run Configurations对话框中,点Java Application,右键–>New,这时会新建一个application名为WordCount

3.3. ?配置运行参数,点Arguments,在Program arguments中输入“你要传给程序的输入文件夹和你要求程序将计算结果保存的文件夹”,如:

hdfs://localhost:9000/user/metaboy/input hdfs://localhost:9000/user/metaboy/output

这里面的input就是你刚传上去文件夹。文件夹地址你可以根据自己具体情况填写。

4.运行程序

点击Run,运行程序,过段时间将运行完成,等运行结束后,可以在终端中用命令:

? ? ?bin/hadoop fs -ls

或者使用插件hadoop eclipse插件查看是否生成文件夹output。

?5. 结果查看

用下面命令查看生成的文件内容:

? ? bin/hadoop fs -cat output/*

运行完这个程序之后,基本上就算是步入到Hadoop这个大家族啦!

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