spark streaming 异常No output streams registered, so nothing to execute

实现spark streaming demo时，代码：

 public static void main (String[] args) {

 SparkConf conf = new SparkConf().setAppName("Spark_Streaming").setMaster("local");
         JavaSparkContext sc = new JavaSparkContext(conf);
         JavaStreamingContext jssc = new JavaStreamingContext(sc, new Duration(2));
         JavaSQLContext sqlCtx = new JavaSQLContext(sc);     

         String[] filters = new String[] {"soc"};

         JavaReceiverInputDStream<Status> receiverStream = TwitterUtils.createStream(jssc,filters);

          jssc.start();
          jssc.awaitTermination();

 }

运行以上代码会出现异常：No output streams registered, so nothing to execute

原因是当发生输出操作的时候，会触发流计算操作，当在 DStream上没有输出操作或者计算时，通常需要执行某些操作，比如以任意方法：

 print()
 foreachRDD(func)
 saveAsObjectFiles(prefix, [suffix])
 saveAsTextFiles(prefix, [suffix])
 saveAsHadoopFiles(prefix, [suffix])

可参考：http://spark.apache.org/docs/latest/streaming-programming-guide.html#output-operations