scala - flatMap 函数中的 Apache Flink Streaming 类型不匹配

Question

尝试在 scala 2.10.4 中使用 0.10.0 flink 版本的流 api。在尝试编译第一个版本时:

import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment
import org.apache.flink.streaming.api.scala.DataStream
import org.apache.flink.streaming.api.windowing.time._

object Main {
  def main(args: Array[String]) {
    val env = StreamExecutionEnvironment.getExecutionEnvironment
    val text = env.socketTextStream("localhost", 9999)

    val words : DataStream[String] = text.flatMap[String](
      new Function[String,TraversableOnce[String]] { 
        def apply(line:String):TraversableOnce[String] = line.split(" ")
      })

    env.execute("Window Stream wordcount")
  }
}

我收到编译时错误:

[error]  found   : String => TraversableOnce[String]
[error]  required: org.apache.flink.api.common.functions.FlatMapFunction[String,String]
[error]       new Function[String,TraversableOnce[String]] { def apply(line:String):TraversableOnce[String] = line.split(" ")})
[error]       ^

在我包含在项目中的 DataStream.class 的反编译版本中，有一些函数可以接受这种类型(最后一个):

public <R> DataStream<R> flatMap(FlatMapFunction<T, R> flatMapper, TypeInformation<R> evidence$12, ClassTag<R> evidence$13) {
        if (flatMapper == null) {
            throw new NullPointerException("FlatMap function must not be null.");
        }
        TypeInformation outType = (TypeInformation)Predef..MODULE$.implicitly(evidence$12);
        return package..MODULE$.javaToScalaStream((org.apache.flink.streaming.api.datastream.DataStream)this.javaStream.flatMap(flatMapper).returns(outType));
    }

    public <R> DataStream<R> flatMap(Function2<T, Collector<R>, BoxedUnit> fun, TypeInformation<R> evidence$14, ClassTag<R> evidence$15) {
        if (fun == null) {
            throw new NullPointerException("FlatMap function must not be null.");
        }
        Function2<T, Collector<R>, BoxedUnit> cleanFun = this.clean((F)fun);
        .anon flatMapper = new /* Unavailable Anonymous Inner Class!! */;
        return this.flatMap((FlatMapFunction<T, R>)flatMapper, evidence$14, evidence$15);
    }

    public <R> DataStream<R> flatMap(Function1<T, TraversableOnce<R>> fun, TypeInformation<R> evidence$16, ClassTag<R> evidence$17) {
        if (fun == null) {
            throw new NullPointerException("FlatMap function must not be null.");
        }
        Function1<T, TraversableOnce<R>> cleanFun = this.clean((F)fun);
        .anon flatMapper = new /* Unavailable Anonymous Inner Class!! */;
        return this.flatMap((FlatMapFunction<T, R>)flatMapper, evidence$16, evidence$17);
    }

这里可能有什么问题？如果您能提供一些见解，我将不胜感激。提前谢谢你。

Answer 1

问题是你正在导入Flink的Java StreamExecutionEnvironment:org.apache.flink.streaming.api.environment.StreamExecutionEnvironment。

您必须像这样使用 StreamExecutionEnvironment 的 Scala 变体:import org.apache.flink.streaming.api.scala.StreamExecutionEnvironment。有了这个改变，一切都在成功构建!

原答案:问题是您将 Function 传递给 flatMap() 方法。但是 flatMap() 需要一个 FlatMapFunction。

 val words : DataStream[String] = text.flatMap[String](
      new FlatMapFunction[String,String] {
        override def flatMap(t: String, collector: Collector[String]): Unit = t.split(" ")
      })