带空字符串验证的Play2.1 JSON格式

我试图在Play2.1中解组到一个对象时验证JSON。我定义的Format对象仅在JSON中缺少字段时进行验证，但我想验证字段是否为非空字符串。这可能吗？我已经尝试在reads（）调用中指定minLength（）约束（如图所示），但是我得到一个编译器错误，说找不到minLength。这只是元组方法吗

请参阅以下Specs2 Junit测试，该测试现在失败，但在正确定义约束后应通过：

import org.specs2.mutable._
import play.api.libs.json._

class SimpleValidation extends SpecificationWithJUnit{

  private val badPayload: JsValue = Json.obj(
    "simpleValue1" -> "mySimpleValue", // Comment this line out to pass test
    "simpleValue2" -> ""
  )

  "An IssueFormat" should {
    "validate when unmarshalling" in {

      badPayload.validate[SimpleObj].fold(
        valid = (res => {
          // Fail if valid
          failure("Payload should have been invalid")
        }),
        invalid = (e => {
          // Should be one error
          e.length mustBeEqualTo(1)
        }))

    }
  }
}

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

case class SimpleObj(simpleValue1: String, simpleValue2: String)
object SimpleObj {
  val simpleReads = (
    (__ \ "simpleValue1").read[String] and
    (__ \ "simpleValue2").read[String])(SimpleObj.apply _) // read[String](minLength(0)) yields compiler error
  val simpleWrites = (
    (__ \ "simpleValue1").write[String] and
    (__ \ "simpleValue2").write[String])(unlift(SimpleObj.unapply))
  implicit val simpleFormat: Format[SimpleObj] = Format(simpleReads, simpleWrites)
} 

---

在浏览了Play2.1文档之后，我添加了一个custome read验证器。如果您将原始问题中的SimpleObj替换为以下内容，测试用例将通过。不确定是否有更简单的方法，但这肯定有效：

object SimpleObj {
  // defines a custom reads to be reused
  // a reads that verifies your value is not equal to a give value
  def notEqual[T](v: T)(implicit r: Reads[T]): Reads[T] = Reads.filterNot(ValidationError("validate.error.unexpected.value", v))(_ == v)

  implicit val simpleReads = (
    (__ \ "simpleValue1").read[String](notEqual("")) and
    (__ \ "simpleValue2").read[String](notEqual("")))(SimpleObj.apply _)

  val simpleWrites = (
    (__ \ "simpleValue1").write[String] and
    (__ \ "simpleValue2").write[String])(unlift(SimpleObj.unapply))
  implicit val simpleFormat: Format[SimpleObj] = Format(simpleReads, simpleWrites)
} 

---

您可以在以下内容中使用minLength：

import play.api.libs.json.Reads._

那么minLength应该可用，但是，请尝试以下格式：

implicit val simpleReads = (
  (__ \ "simpleValue1").read(minLength[String](1)) and
  (__ \ "simpleValue2").read(minLength[String](1))(SimpleObj.apply _)