我们说过Akka-http是一个好的系统集成工具，集成是通过数据交换方式实现的。Http是个在网上传输和接收的规范协议。所以，在使用Akka-http之前，可能我们还是需要把Http模式的网上数据交换细节了解清楚。数据交换双方是通过Http消息类型Request和Response来实现的。在Akka-http中对应的是HttpRequest和HttpResponse。这两个类型都具备HttpEntity类型来装载需要交换的数据。首先，无论如何数据在线上的表现形式肯定是一串bytes。所以，数据交换两头Request,Response中的Entity也必须是以bytes来表达的。在Akka-http里我们把需要传输的数据转换成ByteString，通过网络发送給接收端、接收端再把收到消息Entity中的ByteString转换成目标类型的数据。这两个转换过程就是Akka-http的Marshalling和Unmarshalling过程了。我们先从HttpEntity的构建函数来了解它的定义：
object HttpEntity { ?implicit def apply(string: String): HttpEntity.Strict = apply(ContentTypes.`text/plain(UTF-8)`, string) ?implicit def apply(bytes: Array[Byte]): HttpEntity.Strict = apply(ContentTypes.`application/octet-stream`, bytes) ?implicit def apply(data: ByteString): HttpEntity.Strict = apply(ContentTypes.`application/octet-stream`, data) ?def apply(contentType: ContentType.NonBinary, string: String): HttpEntity.Strict = ???if (string.isEmpty) empty(contentType) else apply(contentType, ByteString(string.getBytes(contentType.charset.nioCharset))) ?def apply(contentType: ContentType, bytes: Array[Byte]): HttpEntity.Strict = ???if (bytes.length == 0) empty(contentType) else apply(contentType, ByteString(bytes)) ?def apply(contentType: ContentType, data: ByteString): HttpEntity.Strict = ???if (data.isEmpty) empty(contentType) else HttpEntity.Strict(contentType, data) ?def apply(contentType: ContentType, contentLength: Long, data: Source[ByteString, Any]): UniversalEntity = ???if (contentLength == 0) empty(contentType) else HttpEntity.Default(contentType, contentLength, data) ?def apply(contentType: ContentType, data: Source[ByteString, Any]): HttpEntity.Chunked = ???HttpEntity.Chunked.fromData(contentType, data)...很明显，HttpEntity可以分两大类，一种是Strict类型的，它的data是ByteString。另一种是UniversalEntity类型，它的数据dataBytes是Source[ByteString,Any]。无论如何最终在线上的还是ByteString。HttpEntity的ContentType注明了传输数据格式，有：
object ContentTypes { ?val `application/json` = ContentType(MediaTypes.`application/json`) ?val `application/octet-stream` = ContentType(MediaTypes.`application/octet-stream`) ?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` ?// used for explicitly suppressing the rendering of Content-Type headers on requests and responses ?val NoContentType = ContentType(MediaTypes.NoMediaType)}注意：ContentType只是一种备注，不影响线上数据表达形式，线上的数据永远是ByteString。但是，其中的application/octet-stream类型代表数据必须是Source[ByteString,Any]。我们下面就通过客户端的例子来理解HttpEntity。下面是一个客户端测试函数：
?def runService(request: HttpRequest, rentity: RequestEntity) = { ??val futResp = for { ????entity <- Future.successful(rentity) ????resp <- Http(sys).singleRequest( ??????request.copy(entity = rentity) ????) ??} yield resp ??futResp ???.andThen { ?????case Success(r@HttpResponse(StatusCodes.OK, _, entity, _)) => ???????entity.dataBytes.map(_.utf8String).runForeach(println) ?????case Success(r@HttpResponse(code, _, _, _)) => ???????println(s"Download request failed, response code: $code") ???????r.discardEntityBytes() ?????case Success(_) => println("Unable to download rows!") ?????case Failure(err) => println(s"Download failed: ${err.getMessage}") ???} ?}我们只需要对这个函数传入RequestEntity就可以了解返回Response里Entity的许多细节了。首先我们要求服务端发送一个纯字符串Hello World。服务端代码如下：
} ~ path("text") { ?????get { ???????complete("Hello World!") ?????} ~虽然complete("Hello World!")有些迷糊，不过应该complete做了些字符串到ByteString的转换。我们可以从上面这个runService函数得到证实。下面是这个例子的调用：
?val reqText = HttpRequest(uri = s"http://localhost:8011/text") ?runService(reqText,HttpEntity.Empty) ???.andThen{case _ => sys.terminate()}从显示的结果可以得出runService函数中的entity.dataBytes.map(_.utf8String)已经把ByteString转换成了String，也就是说服务器端发送的Entity里的数据是ByteString。
我们再试着发送一些数据給服务端，然后让服务端把结果通过response entity返回来：
???} ~ path("text") { ?????get { ???????complete("Hello World!") ?????} ~ ???????post { ?????????withoutSizeLimit { ???????????extractDataBytes { bytes => ?????????????val data = bytes.runFold(ByteString())(_ ++ _) ?????????????onComplete(data) { t => ???????????????complete(t) ?????????????} ???????????} ?????????} ???????}我们看到服务端对request entity的操作是以ByteString进行的。客户端上传一串字符的request如下：
?val postText = HttpRequest(HttpMethods.POST,uri = s"http://localhost:8011/text") ?val uploadText = HttpEntity( ???ContentTypes.`text/plain(UTF-8)`, ???// transform each number to a chunk of bytes ???ByteString("hello world again") ?) ?runService(postText,uploadText) ???.andThen{case _ => sys.terminate()}我们可以看到放进entity里的数据是ByteString。
我们知道Akka-http是基于Akka-Stream的，具备Reactive-Stream功能特性。下面我们就示范一下如何进行stream的上传下载。首先定制一个Source：
?val numbers = Source.fromIterator(() => ???Iterator.continually(Random.nextInt())) ???.map(n => ByteString(s"$n\n")) ?//make conform to withoutSizeLimit constrain ?val source = limitableByteSource(numbers)
服务端也是用HttpEntity来装载这个Source然后通过HttpRequest传给客户端的：
?path("random") { ?????get { ???????complete( ?????????HttpEntity( ???????????ContentTypes.`application/octet-stream`, ???????????// transform each number to a chunk of bytes ???????????source.take(10000) ?????????) ???????) ?????} ~ ?我们在客户端还是用runService来解析传过来的entity。由于接收一个大型的Source，所以需要修改一下接收方式代码：
??futResp ???.andThen { ?????case Success(r@HttpResponse(StatusCodes.OK, _, entity, _)) => ???????val futEnt = entity.dataBytes.map(_.utf8String).runForeach(println) ????????????Await.result(futEnt, Duration.Inf) // throws if binding fails ????????????println("End of stream!!!") ?????case Success(r@HttpResponse(code, _, _, _)) => ???????println(s"Download request failed, response code: $code") ???????r.discardEntityBytes() ?????case Success(_) => println("Unable to download rows!") ?????case Failure(err) => println(s"Download failed: ${err.getMessage}") ???} 用下面的方式调用：
?val reqRandom = HttpRequest(uri = s"http://localhost:8011/random") ???runService(reqRandom,HttpEntity.Empty) ????.andThen{case _ => sys.terminate()}再示范一下在客户端用Source上传数据。服务端代码：
??????post { ?????????withoutSizeLimit { ???????????extractDataBytes { bytes => ?????????????val data = bytes.runFold(ByteString())(_ ++ _) ?????????????onComplete(data) { t => ???????????????complete(t) ?????????????} ???????????} ?????????} ???????}客户端上传数据范例：
val numbers = Source.fromIterator(() => ???Iterator.continually(Random.nextInt())) ???.map(n => ByteString(s"$n\n")) ?//make conform to withoutSizeLimit constrain ?val source = limitableByteSource(numbers) ?val bytes = HttpEntity( ???ContentTypes.`application/octet-stream`, ???// transform each number to a chunk of bytes ???source.take(10000) ?) ?val postRandom = HttpRequest(HttpMethods.POST,uri = s"http://localhost:8011/random") ?runService(postRandom,bytes) ???.andThen{case _ => sys.terminate()}从上面讨论我们了解了在Marshal,Unmarshal下层只是ByteString的操作和转换。下面是本次讨论示范源代码：
服务端：
import akka.actor._import akka.stream._import akka.stream.scaladsl._import akka.http.scaladsl.Httpimport akka.http.scaladsl.server.Directives._import akka.http.scaladsl.model._import akka.util.ByteStringimport akka.http.scaladsl.model.HttpEntity._import scala.util.Randomobject ServerEntity extends App { ?implicit val httpSys = ActorSystem("httpSystem") ?implicit val httpMat = ActorMaterializer() ?implicit val httpEC = httpSys.dispatcher ?val numbers = Source.fromIterator(() => ???Iterator.continually(Random.nextInt())) ???.map(n => ByteString(s"$n\n")) ?//make conform to withoutSizeLimit constrain ?val source = limitableByteSource(numbers) ?val route = ???path("random") { ?????get { ???????withoutSizeLimit { ?????????complete( ???????????HttpEntity( ?????????????ContentTypes.`application/octet-stream`, ?????????????// transform each number to a chunk of bytes ?????????????source.take(1000)) ?????????) ???????} ?????} ~ ???????post { ?????????withoutSizeLimit { ???????????extractDataBytes { bytes => ?????????????val data = bytes.runFold(ByteString())(_ ++ _) ?????????????onComplete(data) { t => ???????????????complete(t) ?????????????} ???????????} ?????????} ???????} ???} ~ path("text") { ?????get { ???????complete("Hello World!") ?????} ~ ???????post { ?????????withoutSizeLimit { ???????????extractDataBytes { bytes => ?????????????val data = bytes.runFold(ByteString())(_ ++ _) ?????????????onComplete(data) { t => ???????????????complete(t) ?????????????} ???????????} ?????????} ???????} ???} ?val (port, host) = (8011,"localhost") ?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())}客户端：
import akka.actor._import akka.stream._import akka.stream.scaladsl._import akka.http.scaladsl.Httpimport akka.http.scaladsl.model.HttpEntity.limitableByteSourceimport akka.http.scaladsl.model._import scala.concurrent.duration._import akka.util.ByteStringimport scala.concurrent._import scala.util._object ClientEntity extends App { ?implicit val sys = ActorSystem("ClientSys") ?implicit val mat = ActorMaterializer() ?implicit val ec = sys.dispatcher ?def runService(request: HttpRequest, rentity: RequestEntity) = { ??val futResp = for { ????entity <- Future.successful(rentity) ????resp <- Http(sys).singleRequest( ??????request.copy(entity = rentity) ????) ??} yield resp ??futResp ???.andThen { ?????case Success(r@HttpResponse(StatusCodes.OK, _, entity, _)) => ???????val futEnt = entity.dataBytes.map(_.utf8String).runForeach(println) ????????????Await.result(futEnt, Duration.Inf) // throws if binding fails ????????????println("End of stream!!!") ?????case Success(r@HttpResponse(code, _, _, _)) => ???????println(s"Download request failed, response code: $code") ???????r.discardEntityBytes() ?????case Success(_) => println("Unable to download rows!") ?????case Failure(err) => println(s"Download failed: ${err.getMessage}") ???} ?} ?val reqText = HttpRequest(uri = s"http://localhost:8011/text")// ?runService(reqText,HttpEntity.Empty)// ???.andThen{case _ => sys.terminate()} ?val postText = HttpRequest(HttpMethods.POST,uri = s"http://localhost:8011/text") ?val uploadText = HttpEntity( ???ContentTypes.`text/plain(UTF-8)`, ???// transform each number to a chunk of bytes ???ByteString("hello world again") ?)// ?runService(postText,uploadText)// ???.andThen{case _ => sys.terminate()} ?val reqRandom = HttpRequest(uri = s"http://localhost:8011/random") // ??runService(reqRandom,HttpEntity.Empty) // ???.andThen{case _ => sys.terminate()} ?val numbers = Source.fromIterator(() => ???Iterator.continually(Random.nextInt())) ???.map(n => ByteString(s"$n\n")) ?//make conform to withoutSizeLimit constrain ?val source = limitableByteSource(numbers) ?val bytes = HttpEntity( ???ContentTypes.`application/octet-stream`, ???// transform each number to a chunk of bytes ???source.take(10000) ?) ?val postRandom = HttpRequest(HttpMethods.POST,uri = s"http://localhost:8011/random") ?runService(postRandom,bytes) ???.andThen{case _ => sys.terminate()}}Akka（38）： Http：Entityof ByteString-数据传输基础
原文地址：http://www.cnblogs.com/tiger-xc/p/7930597.html