JSON读/写错误：应用程序不接受参数

Question

我正在尝试为其中许多值可能为null的case类编写一个Read / Write值。 按照Play框架的教程，我将其编写为

implicit val incomingMessageWrites: Writes[IncomingMessage] = (
        (JsPath \ "stageNum").write[Int] and
        (JsPath \ "stage").write[String] and
        (JsPath \ "stageTime").write[Long] and
        (JsPath \ "vendorId").write[String] and
        (JsPath \ "text").writeNullable[String] and
        (JsPath \ "campaignCode").writeNullable[String] and
        (JsPath \ "osTotals").writeNullable[OSTotals] and
        (JsPath \ "splitSegment").writeNullable[Int] and
        (JsPath \ "segmentNum").writeNullable[Int] and
        (JsPath \ "osBatchStatus").writeNullable[OSBatchStatus]
    )(unlift(IncomingMessage.unapply))

但是，我仍然遇到相同的问题，IntelliJ告诉我，上提方法不起作用，因为“应用程序不接受参数”。

案例类是

case class IncomingMessage(
  stageNum: Int,
  stage: String,
  stageTime: Long,
  vendorId: String,
  text: String,
  campaignCode: String,
  osTotals: OSTotals,
  splitSegment: Int,
  segmentNum: Int,
  osBatchStatus: OSBatchStatus) {

    def this(stageNum: Int, stage: String, stageTime: Long, vendorId: String, text: String, campaignCode: String) =
      this(stageNum, stage, stageTime, vendorId, text, campaignCode, null, 0, 0, null)

    def this(stageNum: Int, stage: String, stageTime: Long, splitSegment: Int, vendorId: String, text: String, campaignCode: String) =
      this(stageNum, stage, stageTime, vendorId, text, campaignCode, null, splitSegment, 0, null)

    def this(stageNum: Int, stage: String, stageTime: Long, segmentNum: Int, vendorId: String) =
      this(stageNum, stage, stageTime, vendorId, null, null, null, 0, segmentNum, null)

    def this(stageNum: Int, stage: String, stageTime: Long, segmentNum: Int, vendorId: String, osTotals: OSTotals) =
      this(stageNum, stage, stageTime, vendorId, null, null, osTotals, 0, segmentNum, null)

    def this(stageNum: Int, stage: String, stageTime: Long, vendorId: String, oSBatchStatus: OSBatchStatus) =
      this(stageNum, stage, stageTime, vendorId, null, null, null, 0, 0, osBatchStatus)

}

其他案例类也会发生相同的情况

case class OSBatchStatus(os: String, success: Int, failure: Int)

object OSBatchStatus {
  implicit val oSBatchStatusReads: Reads[OSBatchStatus] = (
    (JsPath \ "os").readNullable[String] and
      (JsPath \ "success").readNullable[Int] and
      (JsPath \ "failure").readNullable[Int]
    )(OSBatchStatus.apply _)
}

我已经写了Read和Write值，但是省略了它们以节省空间。

任何和所有帮助将不胜感激。

Answer 1

如果输入的JSON文件中有可选字段，那么case类的相应字段也应该是可选字段。 您对OSBatchStatus的Reads定义假定所有字段都是可选的，因此您的case类应如下所示：

case class OSBatchStatus(os: Option[String], success: Option[Int], failure: Option[Int])

相同的规则适用于您的IncomingMessage案例类（必须填写四个字段，而其他每个字段都应该是Option[T] ）。 此外，由于JSON文件中的字段与case类中的字段名称完全相同，因此您可以使用play-json方法为您自动生成Reads/Writes/Format ：

import play.api.libs.functional.syntax._
import play.api.libs.json._

implicit val incomingMessageWrites = Json.writes[IncomingMessage]
implicit val osBatchStatusReads    = Json.reads[OSBatchStatus]
implicit val osTotalsFormat        = Json.format[OSTotals] // Will generate both `Reads` and `Writes`