Spark DF:关于Row中的数值获取问题

//json文件
//{"page_id":"87","pay_category_ids":"99","pay_product_ids":"96","city_id":5}
//{"pay_category_ids":"74","city_id":0} 
val df = sparkSession.read.json("./src/data/test")
df.show()
df.rdd.foreach(row => {
    println("getAs: "+row.getAs[String]("page_id"))
    println("isNull: "+row.isNullAt(1))  //
    val tp = row.getAs[String]("page_id")
    println("==Null:",tp == null)
    println("getLong:", row.getString(1))
   })//json文件
//{"page_id":"87","pay_category_ids":"