Akka-CQRS(11)- akka-http for http-web-service: Marshalling-数据序列化

  前面几篇讨论了关于gRPC方式的前后端连接集成方式。gRPC也是一个开放的标准,但讲到普及性就远远不及基于http/1.1协议的web-service了。特别是gRPC的前端编程还是有一定的门槛,所以作为一种开放的网络大平台还是必须考虑用web-service方式的集成。平台服务api可以有两样选择:一种是传统web-service方式,新的一种是rest api款式。rest api比较适合数据库表的crud操作。在2017年我曾经写了一系列博客介绍akka-http,这里就不再叙述它的细节了。这篇我们只聚焦在解决当前问题上。在POS控制平台例子里不会涉及到POST操作,应该全部是GET类型的,如:

http://192.168.11.189:2588/pos/logon?opr=1010
http://192.168.11.189:2588/pos/logoff
http://192.168.11.189:2588/pos/logsales?acct=001&dpt=01&code=978111&qty=3&price=1200
http://192.168.11.189:2588/pos/subtotal?level=0
http://192.168.11.189:2588/pos/discount?disctype=2&grouped=true&code=481&percent=20

可以看到,请求部分只是带参数的uri,不含entity数据部分,数据通过querystring提供。但返回会有几种数据类型:POSResponse,TxnsItems,vchState,这些都曾经在Protobuffer用IDL定义过: 

message PBVchState {      //单据状态
    string opr  = 1;    //收款员
    int64  jseq = 2;    //begin journal sequence for read-side replay
    int32  num  = 3;    //当前单号
    int32  seq  = 4;    //当前序号
    bool   void = 5;    //取消模式
    bool   refd = 6;    //退款模式
    bool   susp = 7;    //挂单
    bool   canc = 8;    //废单
    bool   due  = 9;    //当前余额
    string su   = 10;   //主管编号
    string mbr  = 11;   //会员号
    int32  mode = 12;   //当前操作流程:0=logOff, 1=LogOn, 2=Payment
}

message PBTxnItem {       //交易记录
    string txndate    = 1;   //交易日期
    string txntime    = 2;   //录入时间
    string opr        = 3;   //操作员
    int32  num        = 4;   //销售单号
    int32  seq        = 5;   //交易序号
    int32  txntype    = 6;   //交易类型
    int32  salestype  = 7;   //销售类型
    int32  qty        = 8;   //交易数量
    int32  price      = 9;   //单价(分)
    int32  amount     = 10;  //码洋(分)
    int32  disc       = 11;  //折扣率 (%)
    int32  dscamt     = 12;  //折扣额:负值  net实洋 = amount + dscamt
    string member     = 13;  //会员卡号
    string code       = 14;  //编号(商品、卡号...)
    string acct       = 15;  //账号
    string dpt        = 16;  //部类
}

message PBPOSResponse {
    int32  sts                  = 1;
    string msg                  = 2;
    PBVchState voucher          = 3;
    repeated PBTxnItem txnitems   = 4;

}

那么概括我们现在的主要工作包括:Uri解析,HttpResponse实例的构建和传输。

首先,用akka-http搭建一个http server框架:

import akka.actor._
import akka.stream._
import akka.http.scaladsl.Http
import akka.http.scaladsl.server.Directives._

object HttpServerDemo extends App {

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

  val route =
    path("hello") {
      complete {"hello, http server "}
    }

  val (port, host) = (8011,"192.168.11.189")

  val bindingFuture = Http().bindAndHandle(route,host,port)

  println(s"Server running at $host $port. Press any key to exit ...")

  scala.io.StdIn.readLine()


  bindingFuture.flatMap(_.unbind())
    .onComplete(_ => httpSys.terminate())

/*
  bindingFuture.foreach(s => println(s.localAddress.getHostString))

  bindingFuture.foreach(_.unbind())

  bindingFuture.onComplete {
    case Success(value) => value.unbind()
  }
*/

}

用akka-http的server api很快就完成了一个简单的http-server。下一步研究一下如何构建返回的HttpResponse:httpresponse是从server端传送到client端的。这个过程包括把HttpResponse Entity里的数据从某种类型转换成通讯用的二进制数据流、到了客户端再转换成目标类型。akka-http的数据转换机制Marshaller/Unmarshaller是通过类型转换的隐式实例来实现的,akka-http提供了多个标准类型数据转换的隐式实例,如StringMarshaller: 

  implicit val ByteArrayMarshaller: ToEntityMarshaller[Array[Byte]] = byteArrayMarshaller(`application/octet-stream`)
  def byteArrayMarshaller(contentType: ContentType): ToEntityMarshaller[Array[Byte]] =
    Marshaller.withFixedContentType(contentType) { bytes => HttpEntity(contentType, bytes) }

  implicit val ByteStringMarshaller: ToEntityMarshaller[ByteString] = byteStringMarshaller(`application/octet-stream`)
  def byteStringMarshaller(contentType: ContentType): ToEntityMarshaller[ByteString] =
    Marshaller.withFixedContentType(contentType) { bytes => HttpEntity(contentType, bytes) }

  implicit val StringMarshaller: ToEntityMarshaller[String] = stringMarshaller(`text/plain`)
  def stringMarshaller(mediaType: MediaType.WithOpenCharset): ToEntityMarshaller[String] =
    Marshaller.withOpenCharset(mediaType) { (s, cs) => HttpEntity(mediaType withCharset cs, s) }
  def stringMarshaller(mediaType: MediaType.WithFixedCharset): ToEntityMarshaller[String] =
    Marshaller.withFixedContentType(mediaType) { s => HttpEntity(mediaType, s) }

...

因为akka-http提供了implicit val StringMarshaller,所以在上面的例子里我可以直接写成: complete("hello world!"),然后系统自动构建一个含字符类型数据entity的HttpResponse。Entity.dataBytes中的数据类型是由Entity.contentType指明的: 

object ContentTypes {
  val `application/json` = ContentType(MediaTypes.`application/json`)
  val `application/octet-stream` = ContentType(MediaTypes.`application/octet-stream`)
  val `application/x-www-form-urlencoded` = ContentType(MediaTypes.`application/x-www-form-urlencoded`)
  val `text/plain(UTF-8)` = MediaTypes.`text/plain` withCharset HttpCharsets.`UTF-8`
  val `text/html(UTF-8)` = MediaTypes.`text/html` withCharset HttpCharsets.`UTF-8`
  val `text/xml(UTF-8)` = MediaTypes.`text/xml` withCharset HttpCharsets.`UTF-8`
  val `text/csv(UTF-8)` = MediaTypes.`text/csv` withCharset HttpCharsets.`UTF-8`

  val `application/grpc+proto` = ContentType(MediaTypes.`application/grpc+proto`)

  // used for explicitly suppressing the rendering of Content-Type headers on requests and responses
  val NoContentType = ContentType(MediaTypes.NoMediaType)
}

客户端收到HttpResponse后把收到的二进制数据流转换成MediaTypes指定的类型。当然,最基本的数据类型就是String了。所有客户端都提供String类型的反序列化deserialization。理论上来讲,我们可以用字符形式来描述任何类型数据,这样我们可以把一个特殊类型实例转成String,然后发送给客户端。客户端再按照协议好的类型转换规则把字符转换成目标类型: 

  case class TextMessage(msg: String)
  val helloMsg: String = TextMessage("hello string message converter").toString
  val route =
    path("hello") {
      complete {helloMsg}
    }

不过,这种情况只适用于内部系统的数据交换,因为数据类型转换的规则方式都是内部私有的。xml,json是开放平台系统数据交换的标准数据类型描述语言,本身是字符String形式的,只是它用String描述类型的语法是行业标准的。客户端可以按行业标准从一个xml/json文件里提取里面的数据类型和实例。所以,自定义类型的数据转换主要包括  类型->jsonstring->bytestring->jsonstring->类型。换句话说我们只要有隐式JsonMarshaller实例就可以完成大部分的数据交换工作了。

spray-json是akka-http自带默认的一个json工具库,它提供了通用的针对任何类型T的Marshaller/Unmarshaller: ToEntityMarshaller[T] 和 FromEntityUnmarshaller[T]。使用spay-json很简单,如下:

import akka.http.scaladsl.marshallers.sprayjson._
import spray.json._

object JsonMarshaller extends  SprayJsonSupport with DefaultJsonProtocol {
  //domain models
  case class Person(name:String, age: Int)
  case class Location(province: String, city: String, zipcode: Int)
  case class Employee(person: Person, loccation: Location)

  //collect your json format instances
  implicit val fmtPerson = jsonFormat2(Person.apply)
  implicit val fmtLocation = jsonFormat3(Location.apply)
  implicit val fmtEmployee = jsonFormat2(Employee.apply)
}

使用Marshaller时只要import JsonMarshaller._ 把几个类型的隐式转换实例带进可视域即可,如下: 

  import JsonMarshaller._

  val person = Person("Jonh Doe", 23)
  val location = Location("GuangDong","ShenZhen",10223)
  val employee = Employee(person,location)

  val route =
    path("json") {
      complete {employee}
    }

就这么简单,试试看:

http://192.168.11.189:8011/json

{"loccation":{"city":"ShenZhen","province":"GuangDong","zipcode":10223},"person":{"age":23,"name":"Jonh Doe"}}

没错,客户端的确收到正确的json数据。还有一项需求是在Reponse里返回一个数据流(多条数据),如当前交易项目清单。这个也比较容易:akka-http本身支持json-streaming。具体使用方法如下: 

  import akka.http.scaladsl.common.EntityStreamingSupport
  import akka.stream.scaladsl._

  implicit val jsonStreamingSupport = EntityStreamingSupport.json()
    .withParallelMarshalling(parallelism = 4, unordered = false)

  val persons = List(person,Person("Peter Kung",28), Person("Ketty Wang",16))
  val personDataSource: Source[Person,Any] = Source.fromIterator(() => persons.iterator)

  val route =
    path("json") {
      complete {employee}
    } ~
    path("stream") {
      complete(personDataSource)
    }

在客户端browser上测试: 

http://192.168.11.189:8011/stream

[{"age":23,"name":"Jonh Doe"},{"age":28,"name":"Peter Kung"},{"age":16,"name":"Ketty Wang"}]

也没问题。下面是本次示范中使用的依赖和它们的版本: 

libraryDependencies ++= Seq(
  "de.heikoseeberger" %% "akka-http-json4s" % "1.26.0",
  "org.json4s" %% "json4s-jackson" % "3.6.6",
  "org.json4s" %% "json4s-ext" % "3.6.6",
  "com.typesafe.akka" %% "akka-http" % "10.1.8" ,
  "com.typesafe.akka" %% "akka-http-spray-json" % "10.1.8",
  "com.typesafe.akka" %% "akka-stream" % "2.5.23"
)

 

 

posted @ 2019-06-19 16:31 雪川大虫 阅读(...) 评论(...) 编辑 收藏