193 DStream相关操作 - Output Operations on DStreams

Output Operations可以将DStream的数据输出到外部的数据库或文件系统，当某个Output Operations原语被调用时（与RDD的Action相同），streaming程序才会开始真正的计算过程。

Output OperationMeaningprint()Prints the first ten elements of every batch of data in a DStream on the driver node running the streaming application. This is useful for development and debugging.saveAsTextFiles(prefix, [suffix])Save this DStream’s contents as text files. The file name at each batch interval is generated based on prefix and suffix: “prefix-TIME_IN_MS[.suffix]”.saveAsObjectFiles(prefix, [suffix])Save this DStream’s contents as SequenceFiles of serialized Java objects. The file name at each batch interval is generated based on prefix and suffix: “prefix-TIME_IN_MS[.suffix]”.saveAsHadoopFiles(prefix, [suffix])Save this DStream’s contents as Hadoop files. The file name at each batch interval is generated based on prefix and suffix: “prefix-TIME_IN_MS[.suffix]”.foreachRDD(func)The most generic output operator that applies a function, func, to each RDD generated from the stream. This function should push the data in each RDD to an external system, such as saving the RDD to files, or writing it over the network to a database. Note that the function func is executed in the driver process running the streaming application, and will usually have RDD actions in it that will force the computation of the streaming RDDs.