Akka(34): Http:Unmarshalling,from Json

  Unmarshalling是Akka-http内把网上可传输格式的数据转变成程序高级结构话数据的过程,比如把Json数据转换成某个自定义类型的实例。按具体流程来说就是先把Json转换成可传输格式数据如:MessageEntity,HttpRequest,HttpReponse等,然后再转换成程序高级结构数据如classXX实例。Unmarshalling对一个A类实例到B类实例的转换是通过Unmarshaller[A,B]来实现的:

trait Unmarshaller[-A, B] extends akka.http.javadsl.unmarshalling.Unmarshaller[A, B] {...}
object Unmarshaller
  extends GenericUnmarshallers
  with PredefinedFromEntityUnmarshallers
  with PredefinedFromStringUnmarshallers {

  // format: OFF

  //#unmarshaller-creation
  /**
   * Creates an `Unmarshaller` from the given function.
   */
  def apply[A, B](f: ExecutionContext ⇒ A ⇒ Future[B]): Unmarshaller[A, B] =
    withMaterializer(ec => _ => f(ec))
...}

从Unmarshaller的构建函数apply可以估计它的作用应该与函数A=>Future[B]很相似。A代表网上可传输类型如MessageEntity、HttpRequest,B代表某种程序高级数据类型。因为A到B的转换是non-blocking的,所以可以立即返回Future类型结果。Akka-http按被转换对象类型分类命名了下面这些类型别名:

type FromEntityUnmarshaller[T] = Unmarshaller[HttpEntity, T]
type FromMessageUnmarshaller[T] = Unmarshaller[HttpMessage, T]
type FromResponseUnmarshaller[T] = Unmarshaller[HttpResponse, T]
type FromRequestUnmarshaller[T] = Unmarshaller[HttpRequest, T]
type FromByteStringUnmarshaller[T] = Unmarshaller[ByteString, T]
type FromStringUnmarshaller[T] = Unmarshaller[String, T]
type FromStrictFormFieldUnmarshaller[T] = Unmarshaller[StrictForm.Field, T]

Akka-http对以下类型提供了自动的Unmarshalling转换: 

PredefinedFromStringUnmarshallers
Byte
Short
Int
Long
Float
Double
Boolean
PredefinedFromEntityUnmarshallers
Array[Byte]
ByteString
Array[Char]
String
akka.http.scaladsl.model.FormData
GenericUnmarshallers
Unmarshaller[T, T] (identity unmarshaller)
Unmarshaller[Option[A], B], if an Unmarshaller[A, B] is available
Unmarshaller[A, Option[B]], if an Unmarshaller[A, B] is available

也就是说Akka-http提供了这些U类型的Unmarshaller[U,B]隐式实例。Akka-http也提供了工具类型Unmarshal:

object Unmarshal {
  def apply[T](value: T): Unmarshal[T] = new Unmarshal(value)
}

class Unmarshal[A](val value: A) {
  /**
   * Unmarshals the value to the given Type using the in-scope Unmarshaller.
   *
   * Uses the default materializer [[ExecutionContext]] if no implicit execution context is provided.
   * If you expect the marshalling to be heavy, it is suggested to provide a specialized context for those operations.
   */
  def to[B](implicit um: Unmarshaller[A, B], ec: ExecutionContext = null, mat: Materializer): Future[B] = {
    val context: ExecutionContext = if (ec == null) mat.executionContext else ec

    um(value)(context, mat)
  }
}

我们可以通过Unmarshal.to[B]把Unmarshal[A]转换成Future[B]。注意:这一步只包括了从网上可传输类型到程序类型转换这一过程,不包括具体实现时的Json转换。下面是一些Unmarshal的用例:

import akka.actor._
import akka.stream._
import akka.http.scaladsl.unmarshalling.Unmarshal
import akka.http.scaladsl.model._
import akka.http.scaladsl.server.Directives._

object Unmarshalling {
  implicit val httpSys = ActorSystem("httpSystem")
  implicit val httpMat = ActorMaterializer()
  implicit val httpEC = httpSys.dispatcher

  val futInt = Unmarshal(43).to[Int]
  val futBoolean = Unmarshal("0").to[Boolean]
  val futString = Unmarshal(HttpEntity("Hello")).to[String]
  val futHello = Unmarshal(HttpRequest(method = HttpMethods.GET, entity = HttpEntity("hello")))

}

以上都是已知类型之间转换,可能没什么实际用途,不像marshalling:中间层Marshalling有实际转换的需要。Unmarshalling可以直接进行Json到自定义类型之间的转换,如:

 val route = (path("User") & post) { entity(as[User]){ user =>
    complete(Future(s"inserting user: $user"))
  }} ~
    (path("Item"/IntNumber) & put) { id => entity(as[Item]){ item =>
      complete(Future(s"update item $id: $item"))
    }}

以上是通过Directive as[???]实现的:

 /**
   * Returns the in-scope [[FromRequestUnmarshaller]] for the given type.
   *
   * @group marshalling
   */
  def as[T](implicit um: FromRequestUnmarshaller[T]) = um

这需要把FromRequestUmarshaller[T]放在可视域内,FromRequestUmarshaller[T]实际是Unmarshaller[T,B]的别名: 

type FromRequestUnmarshaller[T] = Unmarshaller[HttpRequest, T]

在上篇讨论我们介绍了Akka-http的Marshalling是type-class模式的。其中关键可以参考上篇讨论。现在我们需要这些Unmarshaller的隐式实例:

trait Formats extends SprayJsonSupport with DefaultJsonProtocol
object Converters extends Formats {
  case class User(id: Int, name: String)
  case class Item(id: Int, name: String, price: Double)
  implicit val itemFormat = jsonFormat3(Item.apply)
  implicit val userFormat = jsonFormat2(User.apply)
}

object Unmarshalling {
  import Converters._
...

如果使用Json4s的实现方式,我们需要如下提供这些隐式实例:

trait JsonCodec extends Json4sSupport {
  import org.json4s.DefaultFormats
  import org.json4s.ext.JodaTimeSerializers
  implicit val serilizer = jackson.Serialization
  implicit val formats = DefaultFormats ++ JodaTimeSerializers.all
}
object JsConverters extends JsonCodec

Json4s的具体用例如下:

  import scala.collection.mutable._
  case class User(id: Int, name: String)
  class Item(id: Int, name: String, price: Double)
  object AnyPic {
    val area = 10
    val title = "a picture"
    val data = ArrayBuffer[Byte](1,2,3)
  }

  val route = (path("User") & post) { entity(as[User]){ user =>
    complete(Future(s"inserting user: $user"))
  }} ~
    (path("Item"/IntNumber) & put) { id => entity(as[Item]){ item =>
      complete(Future(s"update item $id: $item"))
    }} ~
    (path("Picture") & put) { entity(as[AnyPic.type]){ pic =>
      complete(Future(s"insert picture: $pic"))
    }}

从功能上和表达灵活性来讲,Json4s的实现方式要占优。

下面就是本次讨论的示范源代码:

Unmarshalling

import akka.actor._
import akka.stream._
import akka.http.scaladsl.unmarshalling.Unmarshal
import akka.http.scaladsl.model._
import akka.http.scaladsl.server.Directives._
import scala.concurrent._
import akka.http.scaladsl.marshallers.sprayjson._
import spray.json._

trait Formats extends SprayJsonSupport with DefaultJsonProtocol
object Converters extends Formats {
  case class User(id: Int, name: String)
  case class Item(id: Int, name: String, price: Double)
  implicit val itemFormat = jsonFormat3(Item.apply)
  implicit val userFormat = jsonFormat2(User.apply)
}

object Unmarshalling {
  import Converters._
  implicit val httpSys = ActorSystem("httpSystem")
  implicit val httpMat = ActorMaterializer()
  implicit val httpEC = httpSys.dispatcher

  val futInt = Unmarshal(43).to[Int]
  val futBoolean = Unmarshal("0").to[Boolean]
  val futString = Unmarshal(HttpEntity("Hello")).to[String]
  val futHello = Unmarshal(HttpRequest(method = HttpMethods.GET, entity = HttpEntity("hello")))

  val route = (path("User") & post) { entity(as[User]){ user =>
    complete(Future(s"inserting user: $user"))
  }} ~
    (path("Item"/IntNumber) & put) { id => entity(as[Item]){ item =>
      complete(Future(s"update item $id: $item"))
    }}

}

Json4sUnmarshalling

import akka.actor._
import akka.stream._
import akka.http.scaladsl.server.Directives._
import de.heikoseeberger.akkahttpjson4s.Json4sSupport
import org.json4s.jackson
import scala.concurrent._
trait JsonCodec extends Json4sSupport {
  import org.json4s.DefaultFormats
  import org.json4s.ext.JodaTimeSerializers
  implicit val serilizer = jackson.Serialization
  implicit val formats = DefaultFormats ++ JodaTimeSerializers.all
}
object JsConverters extends JsonCodec


object Json4sUnmarshalling {
  import JsConverters._
  implicit val httpSys = ActorSystem("httpSystem")
  implicit val httpMat = ActorMaterializer()
  implicit val httpEC = httpSys.dispatcher

  import scala.collection.mutable._
  case class User(id: Int, name: String)
  class Item(id: Int, name: String, price: Double)
  object AnyPic {
    val area = 10
    val title = "a picture"
    val data = ArrayBuffer[Byte](1,2,3)
  }

  val route = (path("User") & post) { entity(as[User]){ user =>
    complete(Future(s"inserting user: $user"))
  }} ~
    (path("Item"/IntNumber) & put) { id => entity(as[Item]){ item =>
      complete(Future(s"update item $id: $item"))
    }} ~
    (path("Picture") & put) { entity(as[AnyPic.type]){ pic =>
      complete(Future(s"insert picture: $pic"))
    }}
}

本文参与腾讯云自媒体分享计划,欢迎正在阅读的你也加入,一起分享。

发表于

我来说两句

0 条评论
登录 后参与评论

相关文章

来自专栏腾讯社交用户体验设计

腾讯原创馆,演绎电影人生 - 腾讯ISUX

1225
来自专栏后端技术探索

程序员过生日,机智方式点蜡烛

1. 小区新搬来一户人家,一个30岁左右的年轻女人,带着一个4岁的男孩。每天独自一人操持家务,买菜做饭,接送孩子。时间久了,邻居们都有些议论,直到有一天,一个男...

601
来自专栏区块链大本营

冻结黑客账户!6万EOS被盗的最新仲裁结果出来了

近期大热的EOS版狼人杀遭遇黑客攻击,60686.4190个EOS被盗,上线不到2天的EOS狼人游戏被迫停服。

552
来自专栏科技向令说

【新媒体】16个经典广告创意文案:拿走直接用!

某航天中心的指挥塔内,年轻人马克聚精会神地注视着面前的显示屏。忽然,显示屏上同时出现了两个移动的目标,而且这两个飞行物正越飞越近,有迎头相撞的危险。马克心急如焚...

994
来自专栏Golang语言社区

IT人必读的10个小故事

1.从前,有两个饥饿的人得到了一位长者的恩赐:一根鱼竿和一篓鲜活硕大的鱼。其中, 一个人要了一篓鱼,另一个人要了一根鱼竿,于是他们分道扬镳了。得到鱼的人原地就用...

3468
来自专栏企鹅号快讯

如何向公园里下象棋的大爷们介绍区块链?

“什么是区块链?” 百度百科里是这样说的: 区块链是分布式数据存储、点对点传输、共识机制、加密算法等计算机技术的新型应用模式。 其本质上是一个去中心化的数据库,...

4255
来自专栏数据的力量

中国人骨子里的10大矛盾行为

我们身边或多或少会有这样的人:工作有爹安排,房子老爹给买,车子从爹那儿开,票子说来就来。他们撞人了,对受害者说“我爸是李刚”;他们考挂了,对老师说“我爸是XX”...

791
来自专栏程序员互动联盟

【程序员故事】冤家路窄

程序员的故事,我们的故事。 1、气功神人 收集的速率的确太慢了,网民A逐日上网训练,面临每秒几十K的传输速度,他不得不吸气凝思,耐性期待。一年往后,A成了内地的...

34610
来自专栏数据的力量

跟林彪同志学数据挖掘

2104
来自专栏快讯

颜美身软太会撩 花椒巅峰之战舞王12强主播出炉

2018花椒巅峰之战正在如火如荼的进行中,各品类12强主播即将全面诞生,在近日,经过激烈角逐,巅峰之战“舞王之争”晋级赛也已落下帷幕,TOP12主播“新鲜出炉”...

3709

扫码关注云+社区