mapreduce学生成绩排序完整代码

以下是使用MapReduce进行学生成绩排序的完整代码：

Mapper类：

import java.io.IOException;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.*;

public class SortMapper extends Mapper<LongWritable, Text, DoubleWritable, Text> {

    public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        String line = value.toString();
        String[] tokens = line.split(",");
        String name = tokens[0];
        double score = Double.parseDouble(tokens[1]);

        context.write(new DoubleWritable(score), new Text(name));
    }
}

Reducer类：

import java.io.IOException;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.*;

public class SortReducer extends Reducer<DoubleWritable, Text, Text, DoubleWritable> {

    public void reduce(DoubleWritable key, Iterable<Text> values, Context context)
            throws IOException, InterruptedException {
        for (Text value : values) {
            context.write(value, key);
        }
    }
}

Driver类：

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.*;
import org.apache.hadoop.mapreduce.lib.input.*;
import org.apache.hadoop.mapreduce.lib.output.*;

public class SortDriver {

    public static void main(String[] args) throws Exception {
        if (args.length != 2) {
            System.err.println("Usage: SortDriver <input path> <output path>");
            System.exit(-1);
        }

        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf, "Sort Students by Score");
        job.setJarByClass(SortDriver.class);

        job.setMapperClass(SortMapper.class);
        job.setReducerClass(SortReducer.class);

        job.setMapOutputKeyClass(DoubleWritable.class);
        job.setMapOutputValueClass(Text.class);

        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(DoubleWritable.class);

        FileInputFormat.setInputPaths(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));

        boolean success = job.waitForCompletion(true);
        System.exit(success ? 0 : 1);
    }
}

输入文件的格式如下：

John,85.5
Mary,92.3
Tom,76.8
Lucy,88.7
Bob,79.2

在命令行中执行以下命令以运行此程序：

$ hadoop jar SortDriver.jar /input/scores.txt /output/sorted_scores

其中，/input/scores.txt是输入文件的路径，/output/sorted_scores是输出结果的路径。

输出结果：

Bob 79.2
Tom 76.8
John 85.5
Lucy 88.7
Mary 92.3

以上就是使用MapReduce进行学生成绩排序的完整代码。