不幸的是，我不知道有什么真正好的库可以在 XML 中执行此操作（尽管 Anti-Xml 值得一看）。但是有这样的 Json 库，它是 PlayJson
有了 play json，你基本上可以做所有你可以用 Ruby 的 JsBuilder 做的事情，除了一些范式差异：
Scala 试图尽可能地发挥功能，许多库都使用不可变的数据结构进行操作。玩json也不例外。这意味着您不能仅更改 json 树深处的某些值，您需要重建整个 json 对象
Scala 是一种静态类型语言。这很好，因为编译器检查所有类型签名的正确性，除了我们必须提供这些签名。
下面是示例代码：
import org.joda.time.DateTime
import org.joda.time.format.DateTimeFormat
case class Attachment(fileName: String, url: String)
case class Author(name: String, email: String, url: String)
case class Comment(content: String, created_at: DateTime)
case class Post(author: Author, content: String, attachments: List[Attachment], comments: List[Comment], created_at: DateTime, updated_at: DateTime)
object Main {
import play.api.libs.json._
import play.api.libs.functional.syntax._
val isAdmin = true
def calculateVisits(post: Post) = 35
implicit val jodaTimeWrites: Writes[DateTime] = new Writes[DateTime] {
def writes(c: DateTime): JsValue = {
Json.toJson(c.toString(DateTimeFormat.fullDateTime()))
}
}
implicit val attachmentFormat = Json.format[Attachment]
implicit val authorWrites: Writes[Author] = (
(__ \ "name").write[String] and
(__ \ "email").write[String] and
(__ \ "url").write[String]) { unlift(Author.unapply) }
implicit val commentWrites: Writes[Comment] = (
(__ \ "content").write[String] and
(__ \ "created_at").write[DateTime]) { unlift(Comment.unapply) }
implicit val postWrites: Writes[Post] = (
(__ \ "content").write[String] and
(__ \ "created_at").write[DateTime] and
(__ \ "updated_at").write[DateTime] and
(__ \ "author").write[Author] and
(__ \ "visitors").write[Option[Int]] and
(__ \ "comments").write[List[Comment]] and
(__ \ "attachments").write[List[Attachment]]) { post: Post =>
(
post.content,
post.created_at,
post.updated_at,
post.author,
if (isAdmin) Some(calculateVisits(post)) else None,
post.comments,
post.attachments)
}
def main(args: Array[String]): Unit = {
val post = Post(
Author("David H.", "david@heinemeierhansson.com", "http://example.com/users/1-david.json"),
"<p>This is <i>serious</i> monkey business</p>",
List(
Attachment("forecast.xls", "http://example.com/downloads/forecast.xls"),
Attachment("presentation.pdf", "http://example.com/downloads/presentation.pdf")),
List(
Comment("Hello everyone!", new DateTime()),
Comment("To you my good sir!", new DateTime())),
new DateTime(),
new DateTime())
Console println (Json prettyPrint (Json toJson post))
}
}
注意attachmentFormat - 它是由 scala 宏生成的，用于匹配案例类定义。在我的项目中，我从未编写过一个手动格式覆盖编译器为我生成所有格式！但如果需要，我可以。很好的例子是 jodaTimeWrites - 默认 jodaTimeFormat 将生成更适合机器处理的 long 值，但我已经用我自己的隐式格式覆盖它以匹配 ruby 的示例。
上面的代码产生以下输出：
{
"content" : "<p>This is <i>serious</i> monkey business</p>",
"created_at" : "Friday, July 5, 2013 4:19:42 PM +03:00",
"updated_at" : "Friday, July 5, 2013 4:19:42 PM +03:00",
"author" : {
"name" : "David H.",
"email" : "david@heinemeierhansson.com",
"url" : "http://example.com/users/1-david.json"
},
"visitors" : 35,
"comments" : [ {
"content" : "Hello everyone!",
"created_at" : "Friday, July 5, 2013 4:19:42 PM +03:00"
}, {
"content" : "To you my good sir!",
"created_at" : "Friday, July 5, 2013 4:19:42 PM +03:00"
} ],
"attachments" : [ {
"fileName" : "forecast.xls",
"url" : "http://example.com/downloads/forecast.xls"
}, {
"fileName" : "presentation.pdf",
"url" : "http://example.com/downloads/presentation.pdf"
} ]
}
现在我得到了 33 行 scala 更复杂的映射（没有案例类），而不是 21 行 ruby 代码。为什么要多打字？因为现在我很确定当我通过Comment 而不是Attachment 我会得到编译器错误，或者当我的同事错误地将joda.time.DateFormat 更改为java.util.DateFormat 他会收到错误而不是一些乱码。