Akka(31)： Http：High-Level-Api，Route rejection handling

　　Route 是Akka-http routing DSL的核心部分，使用户能比较方便的从http-server的角度筛选http-request、进行server运算、构建回复的http-response。所谓筛选http-request主要目的是容许request进入下一内层Route，或者拒绝reject request。比如这个～符号：它连接了上下两个独立的Route。如果上面的Route拒绝了一个request，那么下面的Route就会接着尝试这个request。一般来说：当一个筛选功能的Directive如get遇到一个不符合筛选条件的request时，它会拒绝reject这个request进入下一层Route。这时用～符号链接的下一组Route会接着尝试，直到链条最后一组Route。整个过程中的这些rejection事件会被记录下来最后由某个隐式或明式的RejectionHandler实例把这组rejection转化成HttpResponse返回用户。rejection也可以直接调用requestContext.reject(...)产生。Akka-http是通过在运行Route时用Route.seal(route)的方式来确保所有rejection在最终都会得到处理：

　　override def seal(system: ActorSystem, materializer: Materializer): Route = {

　　implicit val s = system

　　implicit val m = materializer

　　RouteAdapter(scaladsl.server.Route.seal(delegate))

　　}

　　下面是Route.seal()函数定义：

　　/**

　　* "Seals" a route by wrapping it with default exception handling and rejection conversion.

　　*

　　* A sealed route has these properties:

　　* - The result of the route will always be a complete response, i.e. the result of the future is a

　　* ``Success(RouteResult.Complete(response))``, never a failed future and never a rejected route. These

　　* will be already be handled using the implicitly given [[RejectionHandler]] and [[ExceptionHandler]] (or

　　* the default handlers if none are given or can be found implicitly).

　　* - Consequently, no route alternatives will be tried that were combined with this route

　　* using the ``~`` on routes or the [[Directive.|]] operator on directives.

　　*/

　　def seal(route: Route)(implicit

　　routingSettings: RoutingSettings,

　　parserSettings: ParserSettings = null,

　　rejectionHandler: RejectionHandler = RejectionHandler.default,

　　exceptionHandler: ExceptionHandler = null): Route = {

　　import directives.ExecutionDirectives._

　　// optimized as this is the root handler for all akka-http applications

　　(handleExceptions(ExceptionHandler.seal(exceptionHandler)) & handleRejections(rejectionHandler.seal))

　　.tapply(_ ⇒ route) // execute above directives eagerly, avoiding useless laziness of Directive.addByNameNullaryApply

　　}

　　RejectionHandler.default是Akka-http提供的默认handler。我们也可以把自定义的隐式RejectionHandler实例放在可视域内就会自动被调用了。下面是一个自定义RejectionHandler例子：

　　RejectionHandler.newBuilder()男性生殖器红肿痒是怎么回事?

　　.handle { case MissingCookieRejection(cookieName) =>

　　complete(HttpResponse(BadRequest, entity = "No cookies, no service!!!"))

　　}

　　.handle { case AuthorizationFailedRejection =>

　　complete((Forbidden, "You're out of your depth!"))

　　}

　　.handle { case ValidationRejection(msg, _) =>

　　complete((InternalServerError, "That wasn't valid! " + msg))

　　}

　　.handleAll[MethodRejection] { methodRejections =>

　　val names = methodRejections.map(_.supported.name)

　　complete((MethodNotAllowed, s"Can't do that! Supported: ${names mkString " or "}!"))

　　}

　　.handleNotFound { complete((NotFound, "Not here!")) }

　　.result()

　　所有Rejection类型都在Rejection.scala里定义。result()函数返回Rejection类型：

　　def result(): RejectionHandler =

　　new BuiltRejectionHandler(cases.result(), notFound, isDefault)

　　我们也可以用mapRejetionResponse对现成handler中产生的HttpResponse进行转换：

　　RejectionHandler.default

　　.mapRejectionResponse {

　　case res @ HttpResponse(_, _, ent: HttpEntity.Strict, _) =>

　　// since all Akka default rejection responses are Strict this will handle all rejections

　　val message = ent.data.utf8String.replaceAll("\"", """\"""")

　　// we copy the response in order to keep all headers and status code, wrapping the message as hand rolled JSON

　　// you could the entity using your favourite marshalling library (e.g. spray json or anything else)

　　res.copy(entity = HttpEntity(ContentTypes.`application/json`, s"""{"rejection": "$message"}"""))

　　case x => x // pass through all other types of responses

　　}

　　下面是一个比较全面的RejectionHandle应用示范：

　　akka.actor._

　　import akka.http.scaladsl.Http

　　import akka.http.scaladsl.model._

　　import akka.http.scaladsl.server._

　　import akka.http.scaladsl.server.Directives._

　　import akka.stream._

　　import akka.stream.scaladsl._

　　import akka._

　　import StatusCodes._

　　import scala.concurrent._

　　object RejectionHandlers {

　　implicit val rejectionHandler =

　　(RejectionHandler.newBuilder()

　　.handle { case MissingCookieRejection(cookieName) =>

　　complete(HttpResponse(BadRequest, entity = "No cookies, no service!!!"))

　　}

　　.handle { case AuthorizationFailedRejection =>

　　complete((Forbidden, "You're out of your depth!"))

　　}

　　.handle { case ValidationRejection(msg, _) =>

　　complete((InternalServerError, "That wasn't valid! " + msg))

　　}

　　.handleAll[MethodRejection] { methodRejections =>阴茎短小吃药可以刺激阴茎增长吗

　　val names = methodRejections.map(_.supported.name)

　　complete((MethodNotAllowed, s"Can't do that! Supported: ${names mkString " or "}!"))

　　}

　　.handleNotFound {

　　extractUnmatchedPath { p =>

　　complete((NotFound, s"The path you requested [${p}] does not exist."))

　　}

　　}

　　.result())

　　.mapRejectionResponse {

　　case res @ HttpResponse(_, _, ent: HttpEntity.Strict, _) =>

　　// since all Akka default rejection responses are Strict this will handle all rejections

　　val message = ent.data.utf8String.replaceAll("\"", """\"""")

　　// we copy the response in order to keep all headers and status code, wrapping the message as hand rolled JSON

　　// you could the entity using your favourite marshalling library (e.g. spray json or anything else)

　　res.copy(entity = HttpEntity(ContentTypes.`application/json`, s"""{"rejection mapped response": "$message"}"""))

　　case x => x // pass through all other types of responses

　　}

　　}

　　object RejectionHandlerDemo extends App {

　　import RejectionHandlers._

　　implicit val httpSys = ActorSystem("httpSys")

　　implicit val httpMat = ActorMaterializer()

　　implicit val httpEc = httpSys.dispatcher

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

　　val route: Flow[HttpRequest, HttpResponse, NotUsed] = pathPrefix("hello" ~ PathEnd) {

　　get {

　　complete {Future("OK")}成都哪家男科医院治疗射精障碍好?

　　//HttpEntity(ContentTypes.`text/html(UTF-8)`,"

　　hello http server

　　")}

　　}

　　}

　　val bindingFuture: Future[Http.ServerBinding] = 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())

　　}