我写了火花作业：
object SimpleApp {
def main(args: Array[String]) {
val conf = new SparkConf().setAppName("Simple Application").setMaster("local")
val sc = new SparkContext(conf)
val ctx = new org.apache.spark.sql.SQLContext(sc)
import ctx.implicits._
case class Person(age: Long, city: String, id: String, lname: String, name: String, sex: String)
case class Person2(name: String, age: Long, city: String)
val persons = ctx.read.json("/tmp/persons.json").as[Person]
persons.printSchema()
}
}
IDE当我运行main函数时，出现2个错误：
Error:(15, 67) Unable to find encoder for type stored in a Dataset. Primitive types (Int, String, etc) and Product types (case classes) are supported by importing sqlContext.implicits._ Support for serializing other types will be added in future releases.
val persons = ctx.read.json("/tmp/persons.json").as[Person]
^
Error:(15, 67) not enough arguments for method as: (implicit evidence$1: org.apache.spark.sql.Encoder[Person])org.apache.spark.sql.Dataset[Person].
Unspecified value parameter evidence$1.
val persons = ctx.read.json("/tmp/persons.json").as[Person]
^
但是在Spark Shell中，我可以毫无错误地运行此作业。问题是什么？
错误消息说Encoder无法采用Person案例类。
Error:(15, 67) Unable to find encoder for type stored in a Dataset. Primitive types (Int, String, etc) and Product types (case classes) are supported by importing sqlContext.implicits._ Support for serializing other types will be added in future releases.
将case类的声明移动到SimpleApp的范围之外。
如果您在SimpleApp中添加sqlContext. int._和_，也会出现同样的错误（顺序无关紧要）。
删除一个或另一个将是解决方案：
val spark = SparkSession
.builder()
.getOrCreate()
val sqlContext = spark.sqlContext
import sqlContext.implicits._ //sqlContext OR spark implicits
//import spark.implicits._ //sqlContext OR spark implicits
case class Person(age: Long, city: String)
val persons = ctx.read.json("/tmp/persons.json").as[Person]
使用Spark 2.1.0测试
有趣的是，如果你添加相同的对象两次，你就不会有问题。
@Milad Khajavi
在对象SimpleApp之外定义Person case类。此外，在main（）函数中添加import sqlContext. implitings。_。
