一、實驗名稱

在Hadoop平臺執行MapReduce程式

二、實驗過程

1.設定環境變數

（1）編輯~/.bashrc檔案，新增下列語句

export HADOOP_HOME=/usr/local/hadoop

export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar:$($HADOOP_HOME/bin/hadoopclasspath):$CLASSPATH

（2）source ~/.bashrc使環境變數生效

2.編譯Java檔案

3.將class檔案打包生成jar檔案

4.開啟HDFS、YARN服務

5.5.上傳檔案計數檔案至HDFS檔案系統中

hdfs相關操作：

hdfs dfs -rm 刪除HDFS檔案系統中的檔案或目錄

hdfs dfs -mkdir 建立目錄

hdfs dfs -ls 列出目錄下所有檔案

hdfs dfs -put 上傳檔案到HDFS

hdfs dfs -get 從HDFS下載檔案到本地

6.在Hadoop平臺中執行MapReduce Job

7.檢視執行結果

8.具體程式

        
import java.io.IOException;
import java.util.*;
        
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.conf.*;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.*;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
        
public class WordCount {
        
 public static class Map extends Mapper<LongWritable, Text, Text, IntWritable> {
    private final static IntWritable one = new IntWritable(1);
    private Text word = new Text();
        
    public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        String line = value.toString();
        StringTokenizer tokenizer = new StringTokenizer(line);
        while (tokenizer.hasMoreTokens()) {
            word.set(tokenizer.nextToken());
            context.write(word, one);
        }
    }
 } 
        
 public static class Reduce extends Reducer<Text, IntWritable, Text, IntWritable> {

    public void reduce(Text key, Iterable<IntWritable> values, Context context) 
      throws IOException, InterruptedException {
        int sum = 0;
        for (IntWritable val : values) {
            sum += val.get();
        }
        context.write(key, new IntWritable(sum));
    }
 }
        
 public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
        
    Job job = new Job(conf, "wordcount");
    
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(IntWritable.class);
        
    job.setMapperClass(Map.class);
    job.setReducerClass(Reduce.class);
        
    job.setInputFormatClass(TextInputFormat.class);
    job.setOutputFormatClass(TextOutputFormat.class);
        
    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));
        
    job.waitForCompletion(true);
 }
        
}