Spark sql 中 窗口函数无法序列化报错 org.apache.spark.SparkException: Task not serializable

参考链接：https://stackoverflow.com/questions/37301241/spark-task-not-serializable-with-lag-window-function

https://www.cnblogs.com/aixing/p/13327364.html

java.io.NotSerializableException: org.apache.spark.sql.expressions.WindowSpec 

因为窗口函数要想继承序列化接口还得自己定义一个类，所以选用的是最简单的方式：加@transient 修饰