Question

我正在尝试实现自定义WritableComparable，如In this link

所示

当我尝试在mapper方法中初始化自定义可写的可比较类时，我收到错误。我在代码中显示了错误。 textpair类应该在sperate文件中吗？

public class Myprog {
    public static class MyMap extends Mapper<Object, Text, TextPair, IntWritable> {
        public void map(Object key, Text value, Context context)
            throws IOException, InterruptedException {
            TextPair writable = new TextPair();

           //ERROR in this line 
           //No enclosing instance of type Myprog is accessible. Must qualify 
           //the allocation with an enclosing instance of type Myprog 
           //(e.g. x.new A() where x is an instance of Myprog).
            ....
    }
}

public static class MyReduce extends Reducer<TextPair, IntWritable, Text, Text> {
    public void reduce(TextPair key, Iterable<IntWritable> values, Context context)
        throws IOException, InterruptedException {
    }
}

public class TextPair implements WritableComparable<TextPair> {
      ....
}

public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
    String[] otherArgs = 
        new GenericOptionsParser(conf, args).getRemainingArgs();
    Collections.addAll(headerList, header.split(","));
    Job job = new Job(conf, "Myprog");
    job.setJarByClass(Myprog.class);
    job.setMapperClass(MyMap.class);
    job.setReducerClass(MyReduce.class);
    job.setMapOutputKeyClass(TextPair.class); 
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(Text.class);

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

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

Answer 1

最好的方法是将TextPair放在一个单独的.java文件中。随着mapper和reducer的增长，将它们放在单独的文件中也会更好话虽这么说，你也可以将你的TextPair类定义为静态，就像你的Mapper和Reducer一样。

Answer 2

您必须将TextPair定义为static。如果没有Myprog的外部实例，则无法实例化它。由于您的Mapper是静态的，因此没有Myprog的实例可供参考。

使用

public static class TextPair

将解决您的问题。

使用Custom WritableComparable时出错

2 个答案: