Scala Play Json - 如何从数组中的元素中读取单个元素？

Question

我有这个 json 对象

val jsonObject = """
 {
  "name" : "camara",
  "project" : {
    "key" : "DOC",
    "name" : "Dockerfiles"
  },
  "cloneUrl" : "https://server/scm/doc/camara.git",
  "links" : {
    "clone" : [ {
      "href" : "https://server/scm/doc/camara.git",
      "name" : "http"
    }, {
      "href" : "ssh://git@server:7999/doc/camara.git",
      "name" : "ssh"
    } ],
    "self" : [ {
      "href" : "url1"
    },
    {
      "href" : "url2"
    } ]
  }
}
"""

在这种情况下 class 和 Reader:

case class Project(name: String, project: String, projectUrl: List[String])

implicit val projectReader: Reads[Project] = (
  (JsPath \ "name").read[String] and
  (JsPath \ "project" \ "name").read[String] and
  (JsPath \ "links" \ "self" \ "href").read[List[String]])(Project.apply _)

我尝试解析这个模型：

Json.parse(jsonObject).validate[Project] match {
  case value: JsSuccess[Project] =>
     println(" >> " + value.get)
  case error: JsError =>
    println(error)
}

我得到这个错误

JsError(List((/links/self//href,List(ValidationError(error.path.result.multiple,WrappedArray())))))

我不知道如何将这些 href 从 self 数组提取到项目 class 中，看起来像这样：

Project(camara,Dockerfiles,List(url1, url2))

我在互联网上到处寻找可以帮助我走上正轨的简单示例，但我还没有找到任何有用的东西。

如何在不更改项目 class 结构的情况下解决此问题？

Answer 1

  import play.api.libs.json._
  import play.api.libs.functional.syntax._
  val jsonObject = """
  {
    "name" : "camara",
    "project" : {
      "key" : "DOC",
      "name" : "Dockerfiles"
    },
    "cloneUrl" : "https://server/scm/doc/camara.git",
    "links" : {
      "clone" : [ {
        "href" : "https://server/scm/doc/camara.git",
        "name" : "http"
      }, {
        "href" : "ssh://git@server:7999/doc/camara.git",
        "name" : "ssh"
      } ],
      "self" : [ {
        "href" : "url1"
      },
      {
        "href" : "url2"
      } ]
    }
  }
  """
  case class Project(name: String, project: String, projectUrl: List[String])

  def multiUrls[T](implicit rt: Reads[T]) = Reads[List[T]] { js =>
    val l: List[JsValue] = (__ \ "links" \ "self" \ "href")(js)
    Json.fromJson[List[T]](JsArray(l))
  }

implicit val projectReader: Reads[Project] = (
  (JsPath \ "name").read[String] and
  (JsPath \ "project" \ "name").read[String] and
  multiUrls[String])(Project.apply _)

  Json.parse(jsonObject).validate[Project] match {
    case value: JsSuccess[Project] =>
       " >> " + value.get
    case error: JsError =>
      error.toString
  }
  // >> Project(camara,Dockerfiles,List(url1, url2))

Answer 2

在你的案例中，JSON 对象的结构没有映射 1:1 到案例 class 上：在 "self" 下面有另一个对象（"href" 属性), 但在你的案例中缺少这个级别 class.

因此您可以修改 JSON 数据或案例 class。

如果你想保留两者，你可以解析成"parse only" case class，解析后将这个转换成"target" case class:

  case class Url(href: String)

  case class ParseProject0(
    name: String,
    project: String,
    projectUrl: List[Url]) {

    def toProject: Project = {
      Project(name, project, projectUrl.map(_.href))
    }
  }

  implicit val urlReader: Reads[Url] = (
    (JsPath \ "href").read[String].map(v => Url(v)))

  implicit val projectReader: Reads[ParseProject] = (
    (JsPath \ "name").read[String] and
      (JsPath \ "project" \ "name").read[String] and
      (JsPath \ "links" \ "self").read[List[Url]])(ParseProject.apply _)

  val parsed = Json.parse(jsonObject)
  val result = parsed.validate[ParseProject] match {
    case value: JsSuccess[ParseProject] =>
      val p = value.get.toProject
      p

    case error: JsError =>
      error
  }

无论如何，在你的 JSON 对象中查看你的 "clone" 属性，看来你仍然需要额外的 class Url，因为对象包含多个属性.

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