IntelliJ IDEA + Maven环境编写第一个hadoop程序

1. 新建IntelliJ下的maven项目

点击File->New->Project，在弹出的对话框中选择Maven，JDK选择你自己安装的版本，点击Next

2. 填写Maven的GroupId和ArtifactId

你可以根据自己的项目随便填，点击Next

这样就新建好了一个空的项目

这里程序名填写WordCount,我们的程序是一个通用的网上的范例,用来计算文件中单词出现的次数

3. 设置程序的编译版本

打开Intellij的Preference偏好设置，定位到Build, Execution, Deployment->Compiler->Java Compiler，

将WordCount的Target bytecode version修改为你的jdk版本(我的是1.8)

4. 配置依赖

编辑pom.xml进行配置

1) 添加apache源

在project内尾部添加

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

2) 添加hadoop依赖

这里只需要用到基础依赖hadoop-core和hadoop-common；如果需要读写HDFS，
则还需要依赖hadoop-hdfs和hadoop-client；如果需要读写HBase，则还需要依赖hbase-client

在project内尾部添加

<dependencies>
    <dependency>
        <groupId>org.apache.hadoop</groupId>
        <artifactId>hadoop-core</artifactId>
        <version>1.2.1</version>
    </dependency>
    <dependency>
        <groupId>org.apache.hadoop</groupId>
        <artifactId>hadoop-common</artifactId>
        <version>2.7.2</version>
    </dependency>
</dependencies>

修改pom.xml完成后，Intellij右上角会提示Maven projects need to be Imported，点击Import Changes以更新依赖,或者点击Enable Auto Import

最后,我的完整的pom.xml如下:

<?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.fun</groupId>
    <artifactId>hadoop</artifactId>
    <version>1.0-SNAPSHOT</version>

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

    <dependencies>
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-core</artifactId>
            <version>1.2.1</version>
        </dependency>
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-common</artifactId>
            <version>2.7.2</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <artifactId>maven-dependency-plugin</artifactId>
                <configuration>
                    <excludeTransitive>false</excludeTransitive>
                    <stripVersion>true</stripVersion>
                    <outputDirectory>./lib</outputDirectory>
                </configuration>

            </plugin>
        </plugins>
    </build>
</project>

5. 编写主程序

WordCount.java

/**
 * Created by jinshilin on 16/12/7.
 */
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);
    }
}

6. 配置输入和输出结果文件夹

1) 添加和src目录同级的input文件夹到项目中

在input文件夹中放置一个或多个输入文件源

我的输入文件源如下:

test.segmented:

dfdfadgdgag
aadads
fudflcl
cckcer
fadf
dfdfadgdgag
fudflcl
fuck
fuck
fuckfuck
haha
aaa

2) 配置运行参数
在Intellij菜单栏中选择Run->Edit Configurations，在弹出来的对话框中点击+，新建一个Application配置。配置Main class为WordCount（可以点击右边的...选择），

Program arguments为input/ output/，即输入路径为刚才创建的input文件夹，输出为output

由于Hadoop的设定，下次运行时务必删除output文件夹！

好了,运行程序,结果如下:

aaa 1
aadads 1
cckcer 1
dfdfadgdgag 2
fadf 1
fuck 2
fuckfuck 1
fudflcl 2
haha 1

至此,一个简单的hadoop程序完成!