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:

1. Intellij Idea 2017.1
2. Maven 3.3.9
3. 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.ConsoleAppenderlog4j.appender.stdout.Target = System.outlog4j.appender.stdout.layout = org.apache.log4j.PatternLayoutlog4j.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  dreama 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   1a   2dream   2have    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/worddir/dream.txt","output"};

八、代码下载

代码下载地址:http://download.csdn.net/detail/napoay/9799523