Kafka Receiver错误 java.lang.IllegalArgumentException: requirement failed: No output operations registered, so nothing to execute

20/04/15 21:46:25 WARN KafkaUtils: overriding receive.buffer.bytes to 65536 see KAFKA-3135
org.apache.spark.streaming.kafka010.DirectKafkaInputDStream@108531c2
20/04/15 21:46:25 ERROR StreamingContext: Error starting the context, marking it as stopped
java.lang.IllegalArgumentException: requirement failed: No output operations registered, so nothing to execute
	at scala.Predef$.require(Predef.scala:224)
	at org.apache.spark.streaming.DStreamGraph.validate(DStreamGraph.scala:168)
	at org.apache.spark.streaming.StreamingContext.validate(StreamingContext.scala:513)
	at org.apache.spark.streaming.StreamingContext.liftedTree1$1(StreamingContext.scala:573)
	at org.apache.spark.streaming.StreamingContext.start(StreamingContext.scala:572)
	at com.kmai.demo02.rua04$.main(rua04.scala:42)
	at com.kmai.demo02.rua04.main(rua04.scala)
Exception in thread "main" java.lang.IllegalArgumentException: requirement failed: No output operations registered, so nothing to execute
	at scala.Predef$.require(Predef.scala:224)
	at org.apache.spark.streaming.DStreamGraph.validate(DStreamGraph.scala:168)
	at org.apache.spark.streaming.StreamingContext.validate(StreamingContext.scala:513)
	at org.apache.spark.streaming.StreamingContext.liftedTree1$1(StreamingContext.scala:573)
	at org.apache.spark.streaming.StreamingContext.start(StreamingContext.scala:572)
	at com.kmai.demo02.rua04$.main(rua04.scala:42)
	at com.kmai.demo02.rua04.main(rua04.scala)
20/04/15 21:46:25 INFO SparkContext: Invoking stop() from shutdown hook
20/04/15 21:46:25 INFO SparkUI: Stopped Spark web UI at http://192.168.100.6:4040
20/04/15 21:46:25 INFO MapOutputTrackerMasterEndpoint: MapOutputTrackerMasterEndpoint stopped!
20/04/15 21:46:25 INFO MemoryStore: MemoryStore cleared
20/04/15 21:46:25 INFO BlockManager: BlockManager stopped
20/04/15 21:46:25 INFO BlockManagerMaster: BlockManagerMaster stopped
20/04/15 21:46:25 INFO OutputCommitCoordinator$OutputCommitCoordinatorEndpoint: OutputCommitCoordinator stopped!
20/04/15 21:46:25 INFO SparkContext: Successfully stopped SparkContext
20/04/15 21:46:25 INFO ShutdownHookManager: Shutdown hook called
20/04/15 21:46:25 INFO ShutdownHookManager: Deleting directory C:\Users\kami\AppData\Local\Temp\spark-15c105c7-9e3b-4098-bfed-381c8b1efb7e

解决原因：代码中没有写DStream的Output Operation操作或者是在使用updateStateByKey算子，没有指定检查点，导致没有触发DStream需要的aciton，所以会报这个错误。
解决方法：使用以下方法之一触发：

print() 
foreachRDD() 
saveAsObjectFiles() 
saveAsTextFiles() 
saveAsHadoopFiles()