WordCount類程式碼：

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.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
 
public class WordCount {
    public static void main(String[] args) throws Exception {
        //定義配置物件
        Configuration conf = new Configuration();
        //定義一個工作物件
        Job job = Job.getInstance(conf);


        //獲取map的一個物件
        job.setMapperClass(WordCountMap.class);
        //指定map階段的一個輸出key
 

        job.setMapOutputKeyClass(Text.class);
        //指定map階段輸出的values型別
        job.setMapOutputValueClass(IntWritable.class);
        //指定map階段的輸入檔案
        FileInputFormat.setInputPaths(job,new Path("D:\\程式碼\\大二下\\Hadoop\\4、MapReduce_Reduce\\123.txt"));


        //獲取reduce的類
        job.setReducerClass(WordCountReduce.class
 
);
        //指定reduce階段的一個輸出的key
        job.setOutputKeyClass(Text.class);
        //指定reduce階段輸出的values型別
        job.setOutputValueClass(IntWritable.class);
        //指定reduce階段的輸出檔案
        FileOutputFormat.setOutputPath(job,new Path("D:\\程式碼\\大二下\\Hadoop\\4、MapReduce_Reduce\\456.txt"));

        job.waitForCompletion(true);
    }
}

WordMap類程式碼：

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

import java.io.IOException;

public class WordCountMap extends Mapper<LongWritable, Text, Text, IntWritable> {
    @Override
    protected void map(LongWritable key, Text value,Context context) throws IOException, InterruptedException {
        //讀取每行文字
        String line = value.toString();
        //splite拆分每行
        String[] words = line.split(" ");
        //取出每個單詞
        for (String word:
             words) {
            //將單詞轉為Text型別
            Text wordText = new Text(word);
            //將1轉變成IntWritable
            IntWritable outValue = new IntWritable(1);
            //寫出每個單詞，跟對應1
            context.write(wordText, outValue);
        }
    }
}

WordReduce類程式碼：

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

import java.io.IOException;
/*
*   Text          輸入的字串型別，序列化
*   IntWritable   輸入一串1，序列化
*   Text          輸出的字串型別，序列化
*   IntWritable   輸出的求和陣列，序列化
* */
public class WordCountReduce extends Reducer<Text, IntWritable,Text,IntWritable> {
    /*
     * key      輸入單詞名字
     * values   輸入一串1
     * context  輸出的工具
     * */
    @Override
    protected void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
        int sum=0;
        for(IntWritable number:values){
            sum += number.get();

        }
        context.write(key,new IntWritable(sum));
    }
}