使用 ArrayWritable 进行序列化似乎以一种有趣的方式工作

我正在与ArrayWritable，在某些时候我需要检查 Hadoop 如何序列化ArrayWritable，这是我通过设置得到的job.setNumReduceTasks(0):

0    IntArrayWritable@10f11b8
3    IntArrayWritable@544ec1
6    IntArrayWritable@fe748f
8    IntArrayWritable@1968e23
11    IntArrayWritable@14da8f4
14    IntArrayWritable@18f6235

这是我正在使用的测试映射器：

public static class MyMapper extends Mapper<LongWritable, Text, LongWritable, IntArrayWritable> {

    public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        int red = Integer.parseInt(value.toString());
        IntWritable[] a = new IntWritable[100];

        for (int i =0;i<a.length;i++){
            a[i] = new IntWritable(red+i);
        }

        IntArrayWritable aw = new IntArrayWritable();
        aw.set(a);
        context.write(key, aw);
    }
}

IntArrayWritable取自javadoc中给出的示例：数组可写.

import org.apache.hadoop.io.ArrayWritable;
import org.apache.hadoop.io.IntWritable;

public class IntArrayWritable extends ArrayWritable {
    public IntArrayWritable() {
        super(IntWritable.class);
    }
}

我实际上检查了 Hadoop 的源代码，这对我来说毫无意义。ArrayWritable不应该序列化类名，并且 100 的数组不可能IntWritable可以使用 6/7 十六进制值进行序列化。该应用程序实际上似乎工作得很好，并且减速器反序列化了正确的值...... 怎么了？我缺少什么？

你必须覆盖默认值toString() method.

它被称为TextOutputFormat创建人类可读的格式。

尝试以下代码并查看结果：

public class IntArrayWritable extends ArrayWritable {
    public IntArrayWritable() {
        super(IntWritable.class);
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        for (String s : super.toStrings())
        {
            sb.append(s).append(" ");
        }
        return sb.toString();
    }
}