我正在尝试使用Twitter作为源执行Spark Streaming示例,如下所示:
public static void main (String.. args) { SparkConf conf = new SparkConf().setAppName("Spark_Streaming_Twitter").setMaster("local"); JavaSparkContext sc = new JavaSparkContext(conf); JavaStreamingContext jssc = new JavaStreamingContext(sc, new Duration(2)); JavaSQLContext sqlCtx = new JavaSQLContext(sc); String[] filters = new String[] {"soccer"}; JavaReceiverInputDStreamreceiverStream = TwitterUtils.createStream(jssc,filters); jssc.start(); jssc.awaitTermination(); }
但我得到以下例外
Exception in thread "main" java.lang.AssertionError: assertion failed: No output streams registered, so nothing to execute at scala.Predef$.assert(Predef.scala:179) at org.apache.spark.streaming.DStreamGraph.validate(DStreamGraph.scala:158) at org.apache.spark.streaming.StreamingContext.validate(StreamingContext.scala:416) at org.apache.spark.streaming.StreamingContext.start(StreamingContext.scala:437) at org.apache.spark.streaming.api.java.JavaStreamingContext.start(JavaStreamingContext.scala:501) at org.learning.spark.TwitterStreamSpark.main(TwitterStreamSpark.java:53)
有任何建议如何解决这个问题?
调用输出运算符时,它会触发流的计算.
如果没有DStream上的输出操作符,则不会调用任何计算.基本上你需要在流上调用以下任何方法
print() foreachRDD(func) saveAsObjectFiles(prefix, [suffix]) saveAsTextFiles(prefix, [suffix]) saveAsHadoopFiles(prefix, [suffix])
http://spark.apache.org/docs/latest/streaming-programming-guide.html#output-operations
您也可以先应用任何转换,然后根据需要输出函数.