Scala使用JSON和/或XML模板

> Scala尽可能地发挥功能,许多库使用不可变数据结构.玩json也不例外.这意味着你不能只在json树中更改一些值,你需要重建整个json对象
> Scala是一种静态类型语言.这很好,因为编译器会检查所有类型签名的正确性,除非我们必须提供这些签名.

这是示例代码：

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))
  }

}

请注意attachmentFormat – 它由scala宏生成,以与case类定义匹配.在我的项目中,我从未编写过单一的手动格式覆盖编译器为我生成所有格式！但我可以,如果我需要.好的例子是jodaTimeWrites – 默认的jodaTimeFormat将生成更长的值,这更适合于机器处理,但我用我自己的隐式格式覆盖它以匹配ruby的样本.

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,"author" : {
    "name" : "David H.","email" : "david@heinemeierhansson.com","url" : "http://example.com/users/1-david.json"
  },"visitors" : 35,"comments" : [ {
    "content" : "Hello everyone!",2013 4:19:42 PM +03:00"
  },{
    "content" : "To you my good sir!",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"
  } ]
}

现在代替21行ruby代码,我得到了33行scala,不知怎的更复杂的映射(没有case类).为何选择更多？因为现在我已经确定当我通过Comment而不是Attachment时我会遇到编译器错误,或者当我的同事将joda.time.DateFormat更改为java.util.DateFormat时,他会收到错误而不是一些乱码.