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我似乎无法为这个特定的 Json 有效负载编写正确的案例类。我相信它与数组中的第一个索引有关，它没有键字符串。关于如何解决这个问题的任何想法？作为参考，我使用的是 Scala 2.10.4、Akka 2.3.2、Spray 1.3.1 和 Lift-Json 2.6。我试图提取的 Json 来自Mailgun 的 Events API。编辑：核心问题是如何提取到 Json 中没有键的案例类？我的代码如下：

import net.liftweb.json._

case class Paging(next : String, previous : String)
case class DeliveryEnvelope(transport : String, sender : String, `sending-ip` : String)
case class DeliveryIndex(tags : List[String], envelope : DeliveryEnvelope)
case class DeliveryStatus(message : String, code : Int, description : String)
case class Flags(`is-authenticated` : Boolean, `is-test-mode` : Boolean)
case class DeliveryMessage(headers : Headers, attachments : Option[List[Object]], recipients : List[String], size : Long)
case class Headers(to : String, `message-id` : String, from : String, subject : String)
case class DeliveryData(index : DeliveryIndex, `delivery-status` : DeliveryStatus,
                    campaigns : List[String], `user-variables` : Object, flags : Flags, timestamp : Double,
                    message : DeliveryMessage, recipient : String, event : String)
case class Delivered(items: List[DeliveryData], paging: Paging)

object Main extends App {
  implicit val formats = DefaultFormats

val json = parse(
""" {
  "items": [
    {
      "tags": [],
      "envelope": {
        "transport": "smtp",
        "sender": "postmaster@samples.mailgun.org",
        "sending-ip": "184.173.153.199"
      },
      "delivery-status": {
        "message": "",
        "code": 0,
        "description": null
      },
      "campaigns": [],
      "user-variables": {},
      "flags": {
        "is-authenticated": true,
        "is-test-mode": false
      },
      "timestamp": 1377208314.173742,
      "message": {
        "headers": {
          "to": "recipient@example.com",
          "message-id": "20130822215151.29325.59996@samples.mailgun.org",
          "from": "sender@example.com",
          "subject": "Sample Message"
        },
        "attachments": [],
        "recipients": [
          "recipient@example.com"
        ],
        "size": 31143
      },
      "recipient": "recipient@example.com",
      "event": "delivered"
    }
  ],
  "paging": {
    "next": "https://api.mailgun.net/v2/samples.mailgun.org/events/W3siYiI6ICIy",
    "previous": "https://api.mailgun.net/v2/samples.mailgun.org/events/W3siYiI6"
  }
} """)
println(compactRender(json))
println(json.extract[Delivered])

和输出：

{"items":[{"tags":[],"envelope":{"transport":"smtp","sender":"postmaster@samples.mailgun.org","sending-ip":"184.173.153.199"},"delivery-status":{"message":"","code":0,"description":null},"campaigns":[],"user-variables":{},"flags":{"is-authenticated":true,"is-test-mode":false},"timestamp":1.377208314173742E9,"message":{"headers":{"to":"recipient@example.com","message-id":"20130822215151.29325.59996@samples.mailgun.org","from":"sender@example.com","subject":"Sample Message"},"attachments":[],"recipients":["recipient@example.com"],"size":31143},"recipient":"recipient@example.com","event":"delivered"}],"paging":{"next":"https://api.mailgun.net/v2/samples.mailgun.org/events/W3siYiI6ICIy","previous":"https://api.mailgun.net/v2/samples.mailgun.org/events/W3siYiI6"}}
Exception in thread "main" net.liftweb.json.MappingException: No usable value for items
No usable value for index
No usable value for envelope
No usable value for transport
Did not find value which can be converted into java.lang.String
   at net.liftweb.json.Meta$.fail(Meta.scala:191)
   at net.liftweb.json.Extraction$.mkValue$1(Extraction.scala:357)
   at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$build$1(Extraction.scala:317)
   at net.liftweb.json.Extraction$$anonfun$14.apply(Extraction.scala:253)
   at net.liftweb.json.Extraction$$anonfun$14.apply(Extraction.scala:253)
   at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
   at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
   at scala.collection.immutable.List.foreach(List.scala:318)
   at scala.collection.TraversableLike$class.map(TraversableLike.scala:244)
   at scala.collection.AbstractTraversable.map(Traversable.scala:105)
   at net.liftweb.json.Extraction$.instantiate$1(Extraction.scala:253)
   at net.liftweb.json.Extraction$.newInstance$1(Extraction.scala:286)
   at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$build$1(Extraction.scala:315)
   at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$extract0(Extraction.scala:366)
   at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$extract0(Extraction.scala:199)
   at net.liftweb.json.Extraction$.extract(Extraction.scala:43)
   at net.liftweb.json.JsonAST$JValue.extract(JsonAST.scala:312)
   at Main$delayedInit$body.apply(Main.scala:87)
   at scala.Function0$class.apply$mcV$sp(Function0.scala:40)
   at scala.runtime.AbstractFunction0.apply$mcV$sp(AbstractFunction0.scala:12)
   at scala.App$$anonfun$main$1.apply(App.scala:71)
   at scala.App$$anonfun$main$1.apply(App.scala:71)
   at scala.collection.immutable.List.foreach(List.scala:318)
   at scala.collection.generic.TraversableForwarder$class.foreach(TraversableForwarder.scala:32)
   at scala.App$class.main(App.scala:71)
   at Main$.main(Main.scala:30)
   at Main.main(Main.scala)
   at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
   at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   at java.lang.reflect.Method.invoke(Method.java:606)
   at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)
Caused by: net.liftweb.json.MappingException: No usable value for index
No usable value for envelope
No usable value for transport
Did not find value which can be converted into java.lang.String
   at net.liftweb.json.Meta$.fail(Meta.scala:191)
   at net.liftweb.json.Extraction$.mkValue$1(Extraction.scala:357)
   at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$build$1(Extraction.scala:317)
   at net.liftweb.json.Extraction$$anonfun$14.apply(Extraction.scala:253)
   at net.liftweb.json.Extraction$$anonfun$14.apply(Extraction.scala:253)
   at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
   at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
   at scala.collection.immutable.List.foreach(List.scala:318)
   at scala.collection.TraversableLike$class.map(TraversableLike.scala:244)
   at scala.collection.AbstractTraversable.map(Traversable.scala:105)
   at net.liftweb.json.Extraction$.instantiate$1(Extraction.scala:253)
   at net.liftweb.json.Extraction$.newInstance$1(Extraction.scala:286)
   at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$build$1(Extraction.scala:315)
   at net.liftweb.json.Extraction$$anonfun$21.apply(Extraction.scala:305)
   at net.liftweb.json.Extraction$$anonfun$21.apply(Extraction.scala:305)
   at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
   at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
   at scala.collection.immutable.List.foreach(List.scala:318)
   at scala.collection.TraversableLike$class.map(TraversableLike.scala:244)
   at scala.collection.AbstractTraversable.map(Traversable.scala:105)
   at net.liftweb.json.Extraction$.newCollection$1(Extraction.scala:305)
   at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$build$1(Extraction.scala:322)
   at net.liftweb.json.Extraction$.mkValue$1(Extraction.scala:351)
... 30 more
Caused by: net.liftweb.json.MappingException: No usable value for envelope
No usable value for transport
Did not find value which can be converted into java.lang.String
   at net.liftweb.json.Meta$.fail(Meta.scala:191)
   at net.liftweb.json.Extraction$.mkValue$1(Extraction.scala:357)
   at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$build$1(Extraction.scala:317)
   at net.liftweb.json.Extraction$$anonfun$14.apply(Extraction.scala:253)
   at net.liftweb.json.Extraction$$anonfun$14.apply(Extraction.scala:253)
   at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
   at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
   at scala.collection.immutable.List.foreach(List.scala:318)
   at scala.collection.TraversableLike$class.map(TraversableLike.scala:244)
   at scala.collection.AbstractTraversable.map(Traversable.scala:105)
   at net.liftweb.json.Extraction$.instantiate$1(Extraction.scala:253)
   at net.liftweb.json.Extraction$.newInstance$1(Extraction.scala:286)
   at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$build$1(Extraction.scala:315)
   at net.liftweb.json.Extraction$.mkValue$1(Extraction.scala:351)
... 51 more
Caused by: net.liftweb.json.MappingException: No usable value for transport
Did not find value which can be converted into java.lang.String
   at net.liftweb.json.Meta$.fail(Meta.scala:191)
   at net.liftweb.json.Extraction$.mkValue$1(Extraction.scala:357)
   at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$build$1(Extraction.scala:317)
   at net.liftweb.json.Extraction$$anonfun$14.apply(Extraction.scala:253)
   at net.liftweb.json.Extraction$$anonfun$14.apply(Extraction.scala:253)
   at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
   at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:244)
   at scala.collection.immutable.List.foreach(List.scala:318)
   at scala.collection.TraversableLike$class.map(TraversableLike.scala:244)
   at scala.collection.AbstractTraversable.map(Traversable.scala:105)
   at net.liftweb.json.Extraction$.instantiate$1(Extraction.scala:253)
   at net.liftweb.json.Extraction$.newInstance$1(Extraction.scala:286)
   at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$build$1(Extraction.scala:315)
   at net.liftweb.json.Extraction$.mkValue$1(Extraction.scala:351)
... 63 more
Caused by: net.liftweb.json.MappingException: Did not find value which can be converted into java.lang.String
   at net.liftweb.json.Meta$.fail(Meta.scala:191)
   at net.liftweb.json.Extraction$.convert(Extraction.scala:403)
   at net.liftweb.json.Extraction$.net$liftweb$json$Extraction$$build$1(Extraction.scala:314)
   at net.liftweb.json.Extraction$.mkValue$1(Extraction.scala:351)
... 75 more
4

2 回答 2

2

感谢大家贡献（或只是查看）我的问题。我通过仅循环 Json 的数据部分解决了我的问题。

val json = parse(STRING HERE)
      val elements = (json \\ "items").children
      for(item <- elements) {
        val data = item.extract[ClickData]

希望这可以帮助其他任何人解决这个或类似的问题。

于 2014-08-16T08:41:41.053 回答
0

您将每个项目映射到 DeliveryData 的一个实例，但在 DeliveryData 中：

  • 您有一个在相应 JSON 中没有值的非可选索引字段。如果该值是可选的，则应将其定义为 Option[DeliveryIndex]
  • 您没有用于映射 JSON 中包含的信封信息的字段。您创建了一个 DeliveryEnvelope 案例类，但它仅由 DeliveryIndex 类引用，并且您发布的 JSON 中不存在 index 字段。
于 2014-08-14T14:26:13.753 回答