Scala/Hadoop:除非存在CustomInputFormat实例，否则使用[CustomInputFormat]类时出现编译器错误

我在

XMLIO.scala

中定义了自定义输入和输出格式：

import scala.xml.Node
import org.apache.hadoop.lib.input.FileInputFormat
import org.apache.hadoop.lib.output.FileOutputFormat
import org.apache.hadoop.mapreduce.{ RecordReader, RecordWriter }
// ...
object XMLIO {
    class XMLInputFormat extends FileInputFormat[LongWritable, Node] { /*...*/ }
    class XMLRecordReader extends RecordReader[LongWritable, Node] { /*...*/ }
    class XMLOutputFormat extends FileOutputFormat[LongWritable, Node] { /*...*/ }
    class XMLRecordWriter extends RecordWriter[LongWritable, Node] { /*...*/ }
}

import XMLIO._
import org.apache.hadoop.conf.Configuration
import org.apache.hadoop.mapreduce.Job
object Example {
    @throws(classOf[Exception])
    def main( args : Array[String] ) {
        val job = new Job(new Configuration(), "")
        job setInputFormatClass classOf[XMLInputFormat]
    }
}

我试图将其用于我在

示例中定义的作业。scala

：

import scala.xml.Node
import org.apache.hadoop.lib.input.FileInputFormat
import org.apache.hadoop.lib.output.FileOutputFormat
import org.apache.hadoop.mapreduce.{ RecordReader, RecordWriter }
// ...
object XMLIO {
    class XMLInputFormat extends FileInputFormat[LongWritable, Node] { /*...*/ }
    class XMLRecordReader extends RecordReader[LongWritable, Node] { /*...*/ }
    class XMLOutputFormat extends FileOutputFormat[LongWritable, Node] { /*...*/ }
    class XMLRecordWriter extends RecordWriter[LongWritable, Node] { /*...*/ }
}

import XMLIO._
import org.apache.hadoop.conf.Configuration
import org.apache.hadoop.mapreduce.Job
object Example {
    @throws(classOf[Exception])
    def main( args : Array[String] ) {
        val job = new Job(new Configuration(), "")
        job setInputFormatClass classOf[XMLInputFormat]
    }
}

但是，这给了我一个编译器错误：

[ERROR] /path/to/Example.scala:8: error: type mismatch;
[INFO]  found   : java.lang.Class[XMLInputFormat](classOf[XMLInputFormat])
[INFO]  required: java.lang.Class[_ <: org.apache.hadoop.mapreduce.InputFormat]
[INFO]     job setInputFormatClass classOf[XMLInputFormat]
[INFO]                                    ^

---

这是怎么回事？有没有一个修复程序看起来不像是一个黑客？

看起来这是scala 2.9.0的一个bug（我正在使用它）。当我升级到scala 2.9.1时，问题就消失了