1.新建IntelliJ下空的的maven專案

直接next即可。

2.配置依賴

編輯pom.xml檔案，新增apache源和hadoop依賴

基礎依賴hadoop-core和hadoop-common；
讀寫HDFS，需要依賴hadoop-hdfs和hadoop-client；
如果需要讀寫HBase，則還需要依賴hbase-client

 <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <name>hadoop</name>
    <url>http://maven.apache.org</url>

    <dependencies>
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-common</artifactId>
            <version>2.8.1</version>
        </dependency>

        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-hdfs</artifactId>
            <version>2.8.1</version>
        </dependency>

        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-client</artifactId>
            <version>2.8.1</version>
        </dependency>

    </dependencies>
 

3.新增core-site.xml到resources檔案

將虛擬機器上的hadoop下/etc/hadoop/core-site.xml檔案拷貝到此專案下resources資料夾下

注意master是我虛擬機器ip地址的對映，如果沒有配置hosts檔案那麼這裡應該填的是你虛擬機器的IP地址。

4.編寫一個WordCount類

WordCount.java

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();
        conf.set("mapreduce.cluster.local.dir","/Users/CHOUKIN/hadoop/var");//在此處有一坑，本地需要新增一個快取資料夾
        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);
    }
}
 

注意：conf.set("mapreduce.cluster.local.dir","/Users/CHOUKIN/hadoop/var");//在此處有一坑，本地需要新增一個快取資料夾
如果沒有這個本地快取資料夾，會報以下錯誤

查詢hadoop官網docs關於mapred-default.xml引數簡介

mapreduce.cluster.local.dir :
The local directory where MapReduce stores intermediate data files. May be a comma-separated list of directories on different devices in order to spread disk i/o. Directories that do not exist are ignored.

這個引數是MapReduce 儲存中間資料檔案的本地目錄。對不同的裝置上的目錄可以用逗號分隔，用以加快磁碟 i/o 。不存在的目錄將被忽略。

5.配置執行引數

在Intellij選單欄中選擇Run->Edit Configurations，在彈出來的對話方塊中點選+，新建一個Application配置。配置Main class為WordCount（可以點選右邊的...選擇），

為Program arguments新增輸入路徑以及輸出路徑，記得把ip地址改為自己虛擬機器的ip地址

6.執行程式

拷貝了一篇滿分英語作文在test.txt裡，執行結果如下

每次執行時檢查hdfs上是否有output資料夾，如果有，請刪除output資料夾。

作者：Chowkin
連結：https://www.jianshu.com/p/41569d558fde
來源：簡書