flink报错This type (GenericType＜＞) cannot be used as key.

原始代码

object TransformTest {
  def main(args: Array[String]): Unit = {
    val env = 
    val stream: DataStreamSource[String] = ("src/main/resources/")
    val value: DataStream[SensorReading] = stream
      .map(a => {
        val arr: Array[String] = (",")
        new SensorReading(arr(0).trim, arr(1)., arr(2).)
  })
    val value1: DataStream[SensorReading] = value
      .keyBy("id")
        .reduce((a,b)=>new SensorReading(,+1,+10))
    ()

    ("tranform")
  }
}
case class SensorReading(id:String,timestamp:Long,temperature:Double)

解决办法

       样例类(实体类)中要有无参构造方法，应把SensorReading类修改如下形式

class SensorReading(){
  var id:String=_
  var timestamp:Long=_
  var temperature:Double=_
  def this(id1:String,timestamp1:Long,temperature1:Double){
    this
    id=id1
    timestamp=timestamp1
    temperature=temperature1
  }
  override def toString: String = id+"+"+timestamp+"+"+temperature
}