spark3.0教程：RDD行动算子aggregate()
spark3.0教程：RDD行动算子foreach()
spark3.0教程：RDD行动算子saveAsSequenceFile
spark3.0教程：RDD行动算子saveAsObjectFile
spark3.0教程：RDD行动算子countByKey()
spark3.0教程：RDD行动算子countByValue()
spark3.0教程：RDD行动算子takeOrdered()
spark3.0教程：RDD行动算子take()
spark3.0教程：RDD行动算子first()
spark3.0教程：RDD行动算子count()