MapReduce编程(一) Intellij Idea配置MapReduce编程环境

介绍怎样在Intellij Idea中通过创建mavenproject配置MapReduce的编程环境。

一、软件环境

我使用的软件版本号例如以下:

1. Intellij Idea 2017.1
2. Maven 3.3.9
3. Hadoop伪分布式环境( 安装教程可參考这里)

二、创建mavenproject

打开Idea,file->new->Project,左側面板选择mavenproject。(假设仅仅跑MapReduce创建javaproject就可以，不用勾选Creat from archetype，假设想创建webproject或者使用骨架能够勾选)



设置GroupId和ArtifactId。下一步。

设置project存储路径。下一步。



Finish之后，空白project的路径例如以下图所看到的。

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完整的project路径例如以下图所看到的：

三、加入maven依赖

在pom.xml加入依赖。对于hadoop 2.7.3版本号的hadoop，须要的jar包有下面几个：

• hadoop-common
• hadoop-hdfs
• hadoop-mapreduce-client-core
• hadoop-mapreduce-client-jobclient

• log4j( 打印日志)

  pom.xml中的依赖例如以下:

    <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。内容例如以下：

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，执行命令：

cd hadoop-2.7.3/
./sbin/start-all.sh

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

六、执行WordCount(从本地读取文件)

在project根目录下新建input目录，input目录下新增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。内容例如以下:

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，内容例如以下:

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);
    }
}

执行完成以后。会在project根目录下添加一个output目录。打开output/part-r-00000，内容例如以下:

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，假设想用main函数的args数组接受參数。在执行时指定输入和输出路径也是能够的。执行WordCount之前，配置Configuration并指定Program arguments就可以。

---

七、执行WordCount(从HDFS读取文件)

在HDFS上新建目录:

hadoop fs -mkdir /worddir

假设出现Namenode安全模式导致的不能创建目录提示：

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

执行下面命令关闭safe mode:

hadoop dfsadmin -safemode leave

上传本地文件:

hadoop fs -put dream.txt /worddir

改动otherArgs參数，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