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

原始代码
object TransformTest {def main(args: Array[String]): Unit = {val env = StreamExecutionEnvironment.getExecutionEnvironmentval 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){thisid=id1timestamp=timestamp1temperature=temperature1}override def toString: String = id+"+"+timestamp+"+"+temperature} 【GenericType＜cn.kgc.SensorReading＞ flink报错This typecannot be used as key.】