hadoop mapreduce 简单例子

本例子统计 用空格分开的单词出现数量（  这个Main.mian 启动方式是hadoop 2.0 的写法。1.0 不一样 ）

目录结构：

使用的 maven ： 下面是maven 依赖。

<dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-client</artifactId>
            <version>2.8.5</version>
        </dependency>

Main.java:

package com.zyk.test;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

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 org.apache.hadoop.util.GenericOptionsParser;

public class Main {

	public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
		Configuration conf = new Configuration();
		GenericOptionsParser optionParser = new GenericOptionsParser(conf, args);
		String[] remainingArgs = optionParser.getRemainingArgs();
		if ((remainingArgs.length != 2) && (remainingArgs.length != 4)) {
			System.err.println("Usage: wordcount <in> <out> [-skip skipPatternFile]");
			System.exit(2);
		}

		Job job = Job.getInstance(conf, "word count");
		job.setJarByClass(Main.class);
		job.setMapperClass(WordMap.class);
		// job.setCombinerClass(IntSumReducer.class);
		job.setReducerClass(WordReduce.class);

		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(LongWritable.class);
		//FileInputFormat.addInputPath(job, new Path("/wd/in"));
		//FileOutputFormat.setOutputPath(job, new Path("/wd/out"));

		List<String> otherArgs = new ArrayList<String>();
		for (int i = 0; i < remainingArgs.length; ++i) {
			if ("-skip".equals(remainingArgs[i])) {
				job.addCacheFile(new Path(remainingArgs[++i]).toUri());
				job.getConfiguration().setBoolean("wordcount.skip.patterns", true);
			} else {
				otherArgs.add(remainingArgs[i]);
			}
		}

		FileInputFormat.addInputPath(job, new Path(otherArgs.get(0)));
		FileOutputFormat.setOutputPath(job, new Path(otherArgs.get(1)));

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

	}

}

　　

WordMap.java

package com.zyk.test;

import java.io.IOException;

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

public class WordMap extends Mapper<LongWritable, Text, Text, LongWritable> {

	@Override
	protected void map(LongWritable key, Text value, Mapper<LongWritable, Text, Text, LongWritable>.Context context)throws IOException, InterruptedException {
		String[] words =  value.toString().split(" ");
		for(String word : words) {
			context.write (new Text( word ), new LongWritable( 1 ) );
		}
	}

}

　　

WordReduce.java

package com.zyk.test;

import java.io.IOException;
import java.util.Iterator;

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

public class WordReduce extends Reducer<Text, LongWritable, Text, LongWritable > {

	@Override
	protected void reduce(Text key, Iterable<LongWritable> arg1,Reducer<Text, LongWritable, Text, LongWritable>.Context context) throws IOException, InterruptedException {

		Iterator<LongWritable> its =	arg1.iterator();

		long sum = 0L;
		while( its.hasNext() ) {
			LongWritable it = its.next();

			sum += it.get();
		}

		context.write( key ,  new LongWritable( sum ) );
	}

}

　　

content.txt  是 要上传到hdfs 上作为输入参数目录的 ，内容我就不提提供了。随便找个页面复制一些文本就可以。

然后打成 jar 包。 发布到hadoop 上运行。（  后面 两个参数是 指定的 输入 和输出路径  ）运行前应该吧  要统计的文件复制到 hdfs 的 /wd/in 目录里面。

./hadoop jar /tools/wd.jar com.zyk.test.Main /wd/in /wd/out4

　　

运行结果：

part-r-00000 打开结果：