如何在Scala Play Framework中解析JSON数组并提取指定字段值

前置说明 #

Play框架内置play-json库专门用于JSON处理，无需额外引入依赖，非Play独立项目可在sbt中添加依赖：

"com.typesafe.play" %% "play-json" % "2.9.4" // 版本可匹配你使用的Play版本调整

方案1：直接遍历JsValue实现 #

无需定义数据结构，直接操作JSON节点：

import play.api.libs.json._

// 你的JSON字符串
val jsonStr: String = """[
  {
    "events": [
      {
        "type": "message",
        "attributes": [
          {"key": "action","value": "withdraw_reward"},
          {"key": "sender","value": "bob"},
          {"key": "module","value": "distribution"},
          {"key": "sender","value": "bob"}
        ]
      },
      {
        "type": "credit",
        "attributes": [
          {"key": "recipient","value": "ross"},
          {"key": "sender","value": "bob"},
          {"key": "amount","value": "100"}
        ]
      },
      {
        "type": "rewards",
        "attributes": [
          {"key": "amount","value": "100"},
          {"key": "validator","value": "sarah"}
        ]
      }
    ]
  },
  {
    "events": [
      {
        "type": "message",
        "attributes": [
          {"key": "action","value": "withdraw_reward"},
          {"key": "sender","value": "bob"},
          {"key": "module","value": "distribution"},
          {"key": "sender","value": "bob"}
        ]
      },
      {
        "type": "credit",
        "attributes": [
          {"key": "recipient","value": "ross"},
          {"key": "sender","value": "bob"},
          {"key": "amount","value": "100"}
        ]
      },
      {
        "type": "rewards",
        "attributes": [
          {"key": "amount","value": "200"},
          {"key": "validator","value": "Ryan"}
        ]
      }
    ]
  }
]"""

// 解析字符串为JsValue
val json: JsValue = Json.parse(jsonStr)

// 核心查询逻辑
val sarahRewardAmount: Option[String] = json.as[JsArray].value
  // 提取所有根节点下的events
  .flatMap(rootItem => (rootItem \ "events").asOpt[JsArray].getOrElse(JsArray.empty).value)
  // 过滤type为rewards的事件
  .filter(event => (event \ "type").asOpt[String].contains("rewards"))
  // 匹配validator为sarah的记录，提取amount
  .flatMap(rewardEvent => {
    // 将attributes转为键值对Map方便查找
    val attrMap = (rewardEvent \ "attributes").asOpt[JsArray].getOrElse(JsArray.empty).value
      .flatMap(attr => for {
        key <- (attr \ "key").asOpt[String]
        value <- (attr \ "value").asOpt[String]
      } yield key -> value).toMap
    
    if (attrMap.get("validator").contains("sarah")) attrMap.get("amount") else None
  })
  // 取第一条符合条件的结果，去掉headOption可获取所有符合条件的集合
  .headOption

// 输出结果：Some("100")
println(sarahRewardAmount)

所有节点取值用asOpt而非as，避免JSON结构不匹配时抛出异常，返回Option类型保证安全。 #

方案2：样例类反序列化实现（更推荐） #

定义对应结构的样例类，利用Play JSON自动反序列化，代码更简洁、类型安全：

import play.api.libs.json._

// 定义和JSON结构匹配的样例类
case class Attribute(key: String, value: String)
case class Event(`type`: String, attributes: Seq[Attribute])
case class RootItem(events: Seq[Event])

// 隐式反序列化规则，Play JSON自动生成
implicit val attrReads: Reads[Attribute] = Json.reads[Attribute]
implicit val eventReads: Reads[Event] = Json.reads[Event]
implicit val rootReads: Reads[RootItem] = Json.reads[RootItem]

// 解析JSON为样例类集合
val items: Seq[RootItem] = json.as[Seq[RootItem]]

// 查询逻辑
val sarahRewardAmount: Option[String] = items
  .flatMap(_.events)
  .filter(_.`type` == "rewards")
  .flatMap(rewardEvent => {
    val attrMap = rewardEvent.attributes.map(attr => attr.key -> attr.value).toMap
    if (attrMap.get("validator").contains("sarah")) attrMap.get("amount") else None
  })
  .headOption

结果说明 #

两种方案最终得到的结果都是Some("100")，如果没有符合条件的记录则返回None，如果需要转为数值类型可调用.map(_.toInt)转换。

内容的提问来源于stack exchange，提问作者bahdotsh