MapReduce排序代码

以下是一个基本的MapReduce排序代码示例：

Mapper函数：

public static class SortMapper extends Mapper<Object, Text, IntWritable, IntWritable>{
    private IntWritable num = new IntWritable();

    public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
        String line = value.toString();
        num.set(Integer.parseInt(line));
        context.write(num, new IntWritable(1));
    }
}

Reducer函数：

public static class SortReducer extends Reducer<IntWritable,IntWritable,IntWritable,IntWritable> {
    private IntWritable rank = new IntWritable(1);

    public void reduce(IntWritable key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
        for (IntWritable value : values) {
            context.write(rank, key);
            rank = new IntWritable(rank.get() + 1);
        }
    }
}

驱动函数：

public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
    Job job = Job.getInstance(conf, "sort");

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

    job.setOutputKeyClass(IntWritable.class);
    job.setOutputValueClass(IntWritable.class);

    job.setMapOutputKeyClass(IntWritable.class);
    job.setMapOutputValueClass(IntWritable.class);

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

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

在这个示例中，Mapper函数将输入文件中的每一行转换为一个整数，并将其作为键输出。值设置为1，因为我们只关心键的数量。在Reducer函数中，我们循环遍历每个键值对，并将它们的排名作为键，原始键作为值输出。驱动函数设置了输入和输出路径，并启动了MapReduce作业。