2

I'm trying to parse JSON in scala and I'm not very successfull. Here's my JSON structure:

{ 
  "data" : "test", 
  "field" : "test", 
  "listObj" : [{ 
      "data" : "testInner1", 
      "field" : "testInner1" 
   } , { 
      "data" : "testInner2", 
      "field" : "testInner2"
   }],
   "obj" : { 
      "data" : "testInner1", 
      "field" : "testInner1" 
   }
}

I'm using lift to parse. Here's my code:

import net.liftweb.json._

implicit val formats = DefaultFormats
case class MyJson(data: String, field: String, obj: MyJson, listObj: List[MyJson])
val json = parse("""
{ 
  "data" : "test", 
  "field" : "test", 
  "listObj" : [{ 
      "data" : "testInner1", 
      "field" : "testInner1" 
   } , { 
      "data" : "testInner2", 
      "field" : "testInner2"
   }],
   "obj" : { 
      "data" : "testInner1", 
      "field" : "testInner1" 
   }
}""")
println(json.extract[Query])

I've god the following exception:

Caused by: net.liftweb.json.MappingException: No usable value for operation
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$13.apply(Extraction.scala:253)
at net.liftweb.json.Extraction$$anonfun$13.apply(Extraction.scala:253)
at scala.collection.TraversableLike$$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$1(Extraction.scala:351)
... 34 more
Caused by: net.liftweb.json.MappingException: Did not find value which can be converted into java.lang.String
at net.liftweb.json.Meta$.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)
... 46 more

I've tried using json4s but I could manage to make it parse into case classes. When I remove the obj and objList from my JSON, it works well.

Anyone can point me out some way to parse this kind of structure to read it in Scala?

4

1 回答 1

3

更改您的案例类定义，使其obj成为可选值：

 case class MyJson(data: String, 
    field: String, 
    // obj: MyJson,        // from 
    obj: Option[MyJson],   // to
    listObj:  List[MyJson])

这是必需的，以便MyJson即使 json 缺少"obj"字段（它在您的示例中的嵌套结构中执行），json 提取器仍然可以生成和实例。

这不是必需的，因为json 中listObj缺少字段仍然可以表示为."listObj"List[MyJson]

于 2013-10-11T04:54:54.410 回答