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

实现spark streaming demo时，代码：

 1 public static void main (String[] args) {
 2
 3
 4 SparkConf conf = new SparkConf().setAppName("Spark_Streaming").setMaster("local");
 5         JavaSparkContext sc = new JavaSparkContext(conf);
 6         JavaStreamingContext jssc = new JavaStreamingContext(sc, new Duration(2));
 7         JavaSQLContext sqlCtx = new JavaSQLContext(sc);
 8
 9
10         String[] filters = new String[] {"soc"};
11
12         JavaReceiverInputDStream<Status> receiverStream = TwitterUtils.createStream(jssc,filters);
13
14
15
16          jssc.start();
17          jssc.awaitTermination();
18
19 }

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：

1 print()
2 foreachRDD(func)
3 saveAsObjectFiles(prefix, [suffix])
4 saveAsTextFiles(prefix, [suffix])
5 saveAsHadoopFiles(prefix, [suffix])

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