Windows+Idea安装Hadoop开发环境

前言：这种问题，本来不应该写篇博客的，但是实在是折磨我太久了，现在终于修好了，必须记一下，否则对不起自己的时间，对自己的博客道歉

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简介

环境：Windows 10+JDK1.8+Intellij Idea，无需手动安装Hadoop

Maven

Maven是项目管理及自动构建工具，由Apache软件基金会所提供。基于项目对象模型（缩写：POM）概念，Maven利用一个pom.xml的文件管理一个项目的构建、报告和文档等步骤。只需要在Maven配置文件中指定Hadoop依赖包名字和版本号，Maven就能自动搞定这些依赖。

Intellij Idea

之所以写这篇博客，就是因为我从Eclipse切换到了Idea产生了很多问题。之前使用Eclipse+Hadoop伪分布式，但是用起来有些不顺手。

WordCount

1.新建项目

2.使用Maven配置Hadoop依赖
完成以上步骤，如果正常将会出现：

箭头所指，即是用来Maven的pom.xml文件，在该文件上填写好依赖，填写好的xml文件为：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
		 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
		 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>com.cmn</groupId>
	<artifactId>test</artifactId>
	<version>1.0-SNAPSHOT</version>

	<repositories>
		<repository>
			<id>apache</id>
			<url>http://maven.apache.org</url>
		</repository>
	</repositories>

	<dependencies>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>4.12</version>
			<scope>test</scope>
		</dependency>

		<dependency>
			<groupId>org.apache.hadoop</groupId>
			<artifactId>hadoop-common</artifactId>
			<version>2.6.1</version>
		</dependency>
		<dependency>
			<groupId>org.apache.hadoop</groupId>
			<artifactId>hadoop-hdfs</artifactId>
			<version>2.6.1</version>
		</dependency>
		<dependency>
			<groupId>commons-cli</groupId>
			<artifactId>commons-cli</artifactId>
			<version>1.2</version>
		</dependency>
		<dependency>
			<groupId>org.apache.hadoop</groupId>
			<artifactId>hadoop-mapreduce-client-core</artifactId>
			<version>2.6.1</version>
		</dependency>
		<dependency>
			<groupId>org.apache.hadoop</groupId>
			<artifactId>hadoop-mapreduce-client-jobclient</artifactId>
			<version>2.6.1</version>
		</dependency>
		<dependency>
			<groupId>log4j</groupId>
			<artifactId>log4j</artifactId>
			<version>1.2.17</version>
		</dependency>
		<dependency>
			<groupId>org.apache.hadoop</groupId>
			<artifactId>hadoop-mapreduce-examples</artifactId>
			<version>2.6.1</version>
		</dependency>
		<dependency>
			<groupId>org.projectlombok</groupId>
			<artifactId>lombok</artifactId>
			<version>1.16.6</version>
		</dependency>
		<dependency>
			<groupId>org.apache.zookeeper</groupId>
			<artifactId>zookeeper</artifactId>
			<version>3.4.8</version>
		</dependency>
	</dependencies>

</project>

分别添加了<repositories></repositories>和<dependencies></dependencies>，Idea会询问是否导入变更，选择Import Changes

3.展开项目目录，src->main->java，在该目录下新建java class，命名为WordCount，WordCount.java文件内容如下：

import java.io.IOException;
import java.util.StringTokenizer;

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.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class WordCount {

	public static class TokenizerMapper
			extends Mapper<Object, Text, Text, IntWritable> {

		private final static IntWritable one = new IntWritable(1);
		private Text word = new Text();

		public void map(Object key, Text value, Context context
		) throws IOException, InterruptedException {
			StringTokenizer itr = new StringTokenizer(value.toString());
			while (itr.hasMoreTokens()) {
				word.set(itr.nextToken());
				context.write(word, one);
			}
		}
	}

	public static class IntSumReducer
			extends Reducer<Text, IntWritable, Text, IntWritable> {
		private IntWritable result = new IntWritable();

		public void reduce(Text key, Iterable<IntWritable> values,
						   Context context
		) throws IOException, InterruptedException {
			int sum = 0;
			for (IntWritable val : values) {
				sum += val.get();
			}
			result.set(sum);
			context.write(key, result);
		}
	}

	public static void main(String[] args) throws Exception {
		Configuration conf = new Configuration();
		Job job = Job.getInstance(conf, "word count");
		job.setJarByClass(WordCount.class);
		job.setMapperClass(TokenizerMapper.class);
		job.setCombinerClass(IntSumReducer.class);
		job.setReducerClass(IntSumReducer.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(IntWritable.class);
		FileInputFormat.addInputPath(job, new Path(args[0]));
		FileOutputFormat.setOutputPath(job, new Path(args[1]));
		System.exit(job.waitForCompletion(true) ? 0 : 1);
	}
}

4.输入代码后，在src目录的同级新建一个Dirctory，命名为input，在里面新建一个文本文件，命名随意，内容随意。完成后目录类似如下：

5.选择File->Project Structure,在右侧的Project Setting中选择Modules，选择Language Level为8 - Lambdas...,如下：

6.选择Run->Run/Debug Configurations->左上角绿色加号->Application，Name填WordCount，MainClass选择WordCount，Program填input/ output/,类似：

7.运行，Run->Run WordCount，等待几秒，结果会出现在output目录下。

可能出现的错误

解决方法：重启你的Idea