package couerse_info;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import java.io.IOException;
/*
stu[0]:课程名称
stu[1]:学生姓名
stu[2]:成绩
stu[3]:性别
stu[4]:年龄
该功能实现的是:通过指定信息查找学生课程考试信息
 */
public class CiMapper extends Mapper<LongWritable,Text,Text,Text> {
    @Override
    protected void map(LongWritable Key1, Text value1,Context context) throws IOException, InterruptedException {
        //将文件的每一行传递过来，使用split分割后利用字符数组进行接收
        String[] splits= value1.toString().split(",");
        //拼接字符串：学生名和成绩
        String course = splits[0];
        String name = splits[1];
        String score = splits[2];
        String course_info = name + "：" + score;
        //向Reducer传递参数-> Key：课程 Value：学生名+成绩
        context.write(new Text(course),new Text(course_info));
    }
}
package couerse_info;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
public class ciReducer extends Reducer<Text, Text,Text, Text> {
    @Override
    protected void reduce(Text key,Iterable<Text> values,Context context)throws IOException,InterruptedException{
       //拼接课程的学生姓名和成绩
        String courseInfo = "\n";
        for(Text Info:values){
            courseInfo = courseInfo + Info + "   ";
        }
        System.out.println(key.toString()+"："+courseInfo);
        System.out.println("***********************************************************************************************************************");
        context.write(key,new Text(courseInfo));
    }
}

package couerse_info;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
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;
import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;
public class CiMain {
    public static void main(String[] args) throws IOException, InterruptedException, ClassNotFoundException, URISyntaxException {
        //创建job和“统计相同课程相同分数的人数”任务入口
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf);
        job.setJarByClass(CiMain.class);
        //设置Mapper和Reducer的入口
        job.setMapperClass(CiMapper.class);
        job.setReducerClass(ciReducer.class);
        //设置Mapper的输入输出类型
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(Text.class);
        //设置Reducer的输入输出类型
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(Text.class);
        //指定输入输出路径
        String inputPath = "hdfs://localhost:9000/mapreduce/input/学生成绩.csv";
        String outputPath = "hdfs://localhost:9000/mapreduce/output/课程信息.txt";
        FileInputFormat.setInputPaths(job,new Path(inputPath));
        FileOutputFormat.setOutputPath(job,new Path(outputPath));
        //输出路径存在的话就删除，不然就只能手动删除，否则会报该文件已存在的异常
        FileSystem fileSystem = FileSystem.get(new URI(outputPath), conf);
        if (fileSystem.exists(new Path(outputPath))) {
            fileSystem.delete(new Path(outputPath), true);
        }
        //执行job
        job.waitForCompletion(true);
    }
}