介绍如何在Intellij Idea中通过创建maven工程配置MapReduce的编程环境。

一、软件环境

我使用的软件版本如下:

Intellij Idea 2017.1
Maven 3.3.9
Hadoop伪分布式环境( 安装教程可参考这里)

二、创建maven工程

打开Idea,file->new->Project,左侧面板选择maven工程。(如果只跑MapReduce创建Java工程即可，不用勾选Creat from archetype，如果想创建web工程或者使用骨架可以勾选)

设置GroupId和ArtifactId，下一步。

设置工程存储路径，下一步。

Finish之后，空白工程的路径如下图所示。

完整的工程路径如下图所示：

三、添加maven依赖

在pom.xml添加依赖，对于Hadoop 2.7.3版本的hadoop，需要的jar包有以下几个：

hadoop-common
hadoop-hdfs
hadoop-mapreduce-client-core
hadoop-mapreduce-client-jobclient
log4j( 打印日志)

pom.xml中的依赖如下:

    <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>2.7.3</version>

        </dependency>

        <dependency>

            <groupId>org.apache.hadoop</groupId>

            <artifactId>hadoop-hdfs</artifactId>

            <version>2.7.3</version>

        </dependency>

        <dependency>

            <groupId>org.apache.hadoop</groupId>

            <artifactId>hadoop-mapreduce-client-core</artifactId>

            <version>2.7.3</version>

        </dependency>

        <dependency>

            <groupId>org.apache.hadoop</groupId>

            <artifactId>hadoop-mapreduce-client-jobclient</artifactId>

            <version>2.7.3</version>

        </dependency>

        <dependency>

            <groupId>log4j</groupId>

            <artifactId>log4j</artifactId>

            <version>1.2.17</version>

        </dependency>

    </dependencies>

四、配置log4j

在src/main/resources目录下新增log4j的配置文件log4j.properties，内容如下：

log4j.rootLogger = debug,stdout

### 输出信息到控制抬 ###

log4j.appender.stdout = org.apache.log4j.ConsoleAppender

log4j.appender.stdout.Target = System.out

log4j.appender.stdout.layout = org.apache.log4j.PatternLayout

log4j.appender.stdout.layout.ConversionPattern = [%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} method:%l%n%m%n

五、启动Hadoop

启动Hadoop，运行命令：

cd hadoop-2.7.3/

./sbin/start-all.sh

访问http://localhost:50070/查看hadoop是否正常启动。

六、运行WordCount(从本地读取文件)

在工程根目录下新建input文件夹，input文件夹下新增dream.txt，随便写入一些单词:

I have a  dream

a dream

在src/main/java目录下新建包，新增FileUtil.java，创建一个删除output文件的函数，以后就不用手动删除了。内容如下:

package com.mrtest.hadoop;

import java.io.File;

/**

 * Created by bee on 3/25/17.

 */

public class FileUtil {

    public static boolean deleteDir(String path) {

        File dir = new File(path);

        if (dir.exists()) {

            for (File f : dir.listFiles()) {

                if (f.isDirectory()) {

                    deleteDir(f.getName());

                } else {

                    f.delete();

                }

            }

            dir.delete();

            return true;

        } else {

            System.out.println("文件(夹)不存在!");

            return false;

        }

    }

}

编写WordCount的MapReduce程序WordCount.java，内容如下:

package com.mrtest.hadoop;

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;

import java.io.IOException;

import java.util.Iterator;

import java.util.StringTokenizer;

/**

 * Created by bee on 3/25/17.

 */

public class WordCount {

    public static class TokenizerMapper extends

            Mapper<Object, Text, Text, IntWritable> {

        public static final 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()) {

                this.word.set(itr.nextToken());

                context.write(this.word, one);

            }

        }

    }

    public static class IntSumReduce 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;

            IntWritable val;

            for (Iterator i = values.iterator(); i.hasNext(); sum += val.get()) {

                val = (IntWritable) i.next();

            }

            this.result.set(sum);

            context.write(key, this.result);

        }

    }

    public static void main(String[] args)

            throws IOException, ClassNotFoundException, InterruptedException {

        FileUtil.deleteDir("output");

        Configuration conf = new Configuration();

        String[] otherArgs = new String[]{"input/dream.txt","output"};

        if (otherArgs.length != 2) {

            System.err.println("Usage:Merge and duplicate removal <in> <out>");

            System.exit(2);

        }

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

        job.setJarByClass(WordCount.class);

        job.setMapperClass(WordCount.TokenizerMapper.class);

        job.setReducerClass(WordCount.IntSumReduce.class);

        job.setOutputKeyClass(Text.class);

        job.setOutputValueClass(IntWritable.class);

        FileInputFormat.addInputPath(job, new Path(otherArgs[0]));

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

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

    }

}

运行完毕以后，会在工程根目录下增加一个output文件夹，打开output/part-r-00000，内容如下:

I   1

a   2

dream   2

have    1

这里在main函数中新增了一个String类型的数组，如果想用main函数的args数组接受参数，在运行时指定输入和输出路径也是可以的。运行WordCount之前，配置Configuration并指定Program arguments即可。

七、运行WordCount(从HDFS读取文件)

在HDFS上新建文件夹:

hadoop fs -mkdir /worddir

如果出现Namenode安全模式导致的不能创建文件夹提示：

mkdir: Cannot create directory /worddir. Name node is in safe mode.

运行以下命令关闭safe mode:

hadoop dfsadmin -safemode leave

上传本地文件:

hadoop fs -put dream.txt /worddir

修改otherArgs参数，指定输入为文件在HDFS上的路径:

String[] otherArgs = new String[]{"hdfs://localhost:9000/wo

验证过程：

巴特西

【转载】MapReduce编程 Intellij Idea配置MapReduce编程环境