org.json4s.MappingException: Classes defined in method bodies are not supported.

Code_LT

已于 2023-04-03 10:24:33 修改

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分类专栏： Error 文章标签： scala servlet

于 2023-03-23 11:13:26 首次发布

本文链接：https://blog.youkuaiyun.com/Code_LT/article/details/129727014

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文章展示了在Scala中使用json4s库时遇到的一个错误，即不能在方法中定义caseclass。通过将caseclass定义移出方法范围，解决了该问题。代码示例包括了caseclass的定义，JSON解析以及从JSON中提取数据到caseclass实例的过程。

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原因是不能方法中定义class

//报错
test("json4s 官网示例3"){
    case class Child(name: String, age: Int, birthdate: Option[java.util.Date])
    case class Address(street: String, city: String)
    case class Person(name: String, address: Address, children: List[Child])
    val json = parse("""
         { "name": "joe",
           "address": {
             "street": "Bulevard",
             "city": "Helsinki"
           },
           "children": [
             {
               "name": "Mary",
               "age": 5,
               "birthdate": "2004-09-04T18:06:22Z"
             },
             {
               "name": "Mazy",
               "age": 3
             }
           ]
         }
       """)
    implicit val formats: Formats = DefaultFormats
    println(json.extract[Person])
    val addressJson = json  \ "address"
    println(addressJson.extract[Address])
    println( (json \ "children").extract[List[Child]])
  }

修改为：

case class Child(name: String, age: Int, birthdate: Option[java.util.Date])
case class Address(street: String, city: String)
case class Person(name: String, address: Address, children: List[Child])
test("json4s 官网示例3"){
    val json = parse("""
         { "name": "joe",
           "address": {
             "street": "Bulevard",
             "city": "Helsinki"
           },
           "children": [
             {
               "name": "Mary",
               "age": 5,
               "birthdate": "2004-09-04T18:06:22Z"
             },
             {
               "name": "Mazy",
               "age": 3
             }
           ]
         }
       """)
    implicit val formats: Formats = DefaultFormats
    println(json.extract[Person])
    val addressJson = json  \ "address"
    println(addressJson.extract[Address])
    println( (json \ "children").extract[List[Child]])
  }