def program(spark: SparkSession): Unit = {
   // RDD ==> DataFrame
   val rdd = spark.sparkContext.textFile("D://data/infos.txt")
   val infoRDD = rdd.map(_.split(",")).map(line => Row(line(0), line(1), line(2)))
   val structType = StructType(Array(StructField("id", StringType, true),
     StructField("name", StringType, true),
     StructField("age", StringType, true)))
   val infoDF = spark.createDataFrame(infoRDD, structType)
   infoDF.printSchema()
   infoDF.show()