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

原始代码

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

    env.execute("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
}