使用 Lift-JSON 解析嵌套 JSON 值时出现问题

Question

我正在使用 Scala 2.12 并尝试解析以下 JSON 文件。

{
    "comp1": {
        "metrics": {
            "operation1": {
                "alias": "activity_operation",
                "weight": 10
            },
            "operation2": {
                "alias": "service_operation",
                "weight": 22
            }
        }
    },
    "comp2": {
        "metrics": {
            "operation1": {
                "alias": "activity_operation",
                "weight": 14
            },
            "operation4": {
                "alias": "service_operation",
                "weight": 16
            }
        }
    }
}

我已将 json 加载到配置变量中，定义了一个案例 class 并尝试了以下操作：

  case class OperationDetails(alias: String, weight: Int)

  for (detail <- (config \ "comp1").children) {
    println(detail.extract[OperationDetails])
  }

这给我错误 Exception in thread "main" net.liftweb.json.MappingException: No usable value for alias. Did not find value which can be converted into java.lang.String

我无法使用“operation1”检索子项，因为操作是随机的。

我需要检索操作名称 operation1, operation2, operation4, .. 及其各自的别名和权重。有什么想法吗？

Answer 1

您至少缺少一层嵌套，并且可能还缺少隐式 val formats。

这将打印所有操作。请注意转换为 JObject 以便能够检索字段名称。

  // Setup 
  case class Operation(alias: String, weight: Int)
  implicit val formats = DefaultFormats

  // Traversal
  val comps: List[JsonAST.JValue] = config.children
  for (comp <- comps) {
    val metrics:List[JsonAST.JValue] = comp.children
    for (metric <- metrics) {
      val operations:List[JsonAST.JField] = metric.asInstanceOf[JObject].obj
      for (operation <- operations) {
        val op = operation.value.extract[Operation]
        // Do something here
        println(s"${operation.name}:(${op.alias},${op.weight})")
      }
    }
  }

输出：

operation1:(activity_operation,10)
operation2:(service_operation,22)
operation1:(activity_operation,14)
operation4:(service_operation,16)

使用 Lift-JSON 解析嵌套 JSON 值时出现问题

Issue with parsing nested JSON values with Lift-JSON

json

scala

lift-json