Ananth Duari Ananth Duari - 4 months ago 46
Java Question

Spark Streaming with Twitter - No output streams registered, so nothing to execute

I'm trying to execute a spark streaming example using Twitter. This is my code

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"};

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



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

}


But I'm getting the following exception

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)


Any suggestion how to fix this issue?

Answer

When an output operator is called, it triggers the computation of a stream.

Without output operator on DStream no computation is invoked. basically you will need to invoke any of below method on stream

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

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

you can also first apply any transformations and then output functions too if required.

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