上篇提到，按当前对web-service功能需要，我们需要完成数据转换marshalling，服务接口routing这两部分的调研和示范。上篇已经完成了对序列化marshalling的讨论，这篇就介绍一下routing了。akka-http提供了一套功能强大，使用又很方便的Routing DSL。Route是个类型：
type Route = RequestContext ⇒ Future[RouteResult]
实际上就是个把HttpRequest转换成HttpResponse的函数。举个例子：
val route: Flow[HttpRequest, HttpResponse, NotUsed]=
get {
pathSingleSlash {
complete(HttpEntity(ContentTypes.`text/html(UTF-8)`,"Hello world!"))
} ~
path("ping") {
complete("PONG!")
} ~
path("crash") {
sys.error("BOOM!")
}
}
这个route是个handler Flow, 但Route可以用RouteResult.route2HandlerFlow转换成Flow:
/**
* Turns a `Route` into a server flow.
*
* This conversion is also implicitly available through [[RouteResult#route2HandlerFlow]].
*/
def handlerFlow(route: Route)(implicit
routingSettings: RoutingSettings,
parserSettings: ParserSettings,
materializer: Materializer,
routingLog: RoutingLog,
executionContext: ExecutionContextExecutor = null,
rejectionHandler: RejectionHandler = RejectionHandler.default,
exceptionHandler: ExceptionHandler = null): Flow[HttpRequest, HttpResponse, NotUsed] =
Flow[HttpRequest].mapAsync(1)(asyncHandler(route))
...
implicit def route2HandlerFlow(route: Route)(
implicit
routingSettings: RoutingSettings,
parserSettings: ParserSettings,
materializer: Materializer,
routingLog: RoutingLog,
executionContext: ExecutionContext = null,
rejectionHandler: RejectionHandler = RejectionHandler.default,
exceptionHandler: ExceptionHandler = null
): Flow[HttpRequest, HttpResponse, NotUsed] =
Route.handlerFlow(route)
route是由Directive类组合而成的一个决策树decision-tree。get、path、pathSingleSlash等都是Directive, 如：
def path[L](pm: PathMatcher[L]): Directive[L] = pathPrefix(pm ~ PathEnd)
然后complete返回Route类：
def complete(m: ⇒ ToResponseMarshallable): StandardRoute =
StandardRoute(_.complete(m))
...
abstract class StandardRoute extends Route {
def toDirective[L: Tuple]: Directive[L] = StandardRoute.toDirective(this)
}
Directive的主要功能就是对HttpRequest的Uri进行解析，找出具体的服务接口点，已经对entity里的数据进行调取。
Route是一种可组合组件。我们可以用简单的Route组合成更多层次的Route。下面是组合Route的几种方式：
1、Route转化：对输入的request，输出的response进行转化处理后把实际运算托付给下一层内部（inner）Route
2、筛选Route：只容许符合某种条件的Route通过并拒绝其它不符合条件的Route
3、链接Route：假如一个Route被拒绝，尝试下一个Route。这个是通过 ～ 操作符号实现的
在Akka-http的routing DSL里这些Route组合操作是通过Directive实现的。Akka-http提供了大量现成的Directive，我们也可以自定义一些特殊功能的Directive，详情可以查询官方文件或者api文件。
Directive的表达形式如下：
dirname(arguments) { extractions =>
... // 内层inner route
}
下面是Directive的一些用例：
下面的三个route效果相等：
val route: Route = { ctx =>
if (ctx.request.method == HttpMethods.GET)
ctx.complete("Received GET")
else
ctx.complete("Received something else")
}
val route =
get {
complete("Received GET")
} ~
complete("Received something else")
val route =
get { ctx =>
ctx.complete("Received GET")
} ~
complete("Received something else")
下面列出一些Directive的组合例子：
val route: Route =
path("order" / IntNumber) { id =>
get {
complete {
"Received GET request for order " + id
}
} ~
put {
complete {
"Received PUT request for order " + id
}
}
}
def innerRoute(id: Int): Route =
get {
complete {
"Received GET request for order " + id
}
} ~
put {
complete {
"Received PUT request for order " + id
}
}
val route: Route = path("order" / IntNumber) { id => innerRoute(id) }
val route =
path("order" / IntNumber) { id =>
(get | put) { ctx =>
ctx.complete(s"Received ${ctx.request.method.name} request for order $id")
}
}
val route =
path("order" / IntNumber) { id =>
(get | put) {
extractMethod { m =>
complete(s"Received ${m.name} request for order $id")
}
}
}
val getOrPut = get | put
val route =
path("order" / IntNumber) { id =>
getOrPut {
extractMethod { m =>
complete(s"Received ${m.name} request for order $id")
}
}
}
val route =
(path("order" / IntNumber) & getOrPut & extractMethod) { (id, m) =>
complete(s"Received ${m.name} request for order $id")
}
val orderGetOrPutWithMethod =
path("order" / IntNumber) & (get | put) & extractMethod
val route =
orderGetOrPutWithMethod { (id, m) =>
complete(s"Received ${m.name} request for order $id")
}
我们可以从上面这些示范例子得出结论：Directive的组合能力是routing DSL的核心。来看看Directive的组合能力是如何实现的。Directive类定义如下：
//#basic
abstract class Directive[L](implicit val ev: Tuple[L]) {
/**
* Calls the inner route with a tuple of extracted values of type `L`.
*
* `tapply` is short for "tuple-apply". Usually, you will use the regular `apply` method instead,
* which is added by an implicit conversion (see `Directive.addDirectiveApply`).
*/
def tapply(f: L ⇒ Route): Route
...
}
/**
* Constructs a directive from a function literal.
*/
def apply[T: Tuple](f: (T ⇒ Route) ⇒ Route): Directive[T] =
new Directive[T] { def tapply(inner: T ⇒ Route) = f(inner) }
/**
* A Directive that always passes the request on to its inner route (i.e. does nothing).
*/
val Empty: Directive0 = Directive(_(()))
...
implicit class SingleValueModifiers[T](underlying: Directive1[T]) extends AnyRef {
def map[R](f: T ⇒ R)(implicit tupler: Tupler[R]): Directive[tupler.Out] =
underlying.tmap { case Tuple1(value) ⇒ f(value) }
def flatMap[R: Tuple](f: T ⇒ Directive[R]): Directive[R] =
underlying.tflatMap { case Tuple1(value) ⇒ f(value) }
def require(predicate: T ⇒ Boolean, rejections: Rejection*): Directive0 =
underlying.filter(predicate, rejections: _*).tflatMap(_ ⇒ Empty)
def filter(predicate: T ⇒ Boolean, rejections: Rejection*): Directive1[T] =
underlying.tfilter({ case Tuple1(value) ⇒ predicate(value) }, rejections: _*)
}
}
注意Directive.apply参数f: (T =>Route)=>Route)， 代表 dirname (args){extractions => ...} 这样的构建函数款式。还有implicit ev: Tuple[L]是给compiler的证例，它要求Tuple[L]存在于可视域。Akka-http提供了所有22个TupleXX[L]的隐形实例。再注意implicit class singleValueModifiers[T]：它提供了多层Directive的自动展平，能够实现下面的自动转换结果：
Directive1[T] = Directive[Tuple1[T]]
Directive1[Tuple2[M,N]] = Directive[Tuple1[Tuple2[M,N]]] = Directive[Tuple2[M,N]]
Directive1[Tuple3[M,N,G]] = ... = Directive[Tuple3[M,N,G]]
Directive1[Tuple4[M1,M2,M3,M4]] = ... = Directive[Tuple4[M1,M2,M3,M4]]
...
Directive1[Unit] = Directive0
Directive1,Directive0：
type Directive0 = Directive[Unit]
type Directive1[T] = Directive[Tuple1[T]]
下面是这几种Directive的使用模式：
dirname { route } //Directive0
dirname[L] { L => route } //Directive1[L]
dirname[T] { (T1,T2...) => route} //Directive[T]
任何类型值到Tuple的自动转换是通过Tupler类实现的：
/**
* Provides a way to convert a value into an Tuple.
* If the value is already a Tuple then it is returned unchanged, otherwise it's wrapped in a Tuple1 instance.
*/
trait Tupler[T] {
type Out
def OutIsTuple: Tuple[Out]
def apply(value: T): Out
}
object Tupler extends LowerPriorityTupler {
implicit def forTuple[T: Tuple]: Tupler[T] { type Out = T } =
new Tupler[T] {
type Out = T
def OutIsTuple = implicitly[Tuple[Out]]
def apply(value: T) = value
}
}
private[server] abstract class LowerPriorityTupler {
implicit def forAnyRef[T]: Tupler[T] { type Out = Tuple1[T] } =
new Tupler[T] {
type Out = Tuple1[T]
def OutIsTuple = implicitly[Tuple[Out]]
def apply(value: T) = Tuple1(value)
}
}
好了，还是回到具体的Uri解析上来吧。在POS例子里需要上传的指令款式如下：
http://192.168.11.189:2588/pos/logon?shopid=1101&opr=1010
http://192.168.11.189:2588/pos/logoff?shopid=1101
http://192.168.11.189:2588/pos/logsales?shopid=1101&acct=001&dpt=01&code=978111&qty=3&price=1200
http://192.168.11.189:2588/pos/shopid=1101&subtotal?level=0
http://192.168.11.189:2588/pos/shopid=1101&discount?disctype=2&grouped=true&code=481&percent=20
基本上全部是Uri Path解析的工作。下面是具体的Route示范：
val route =
(pathPrefix("pos-on-cloud") & get) {
((pathSuffix("logon") & parameters('shopid.as[Int], 'opr)){ (id, op) =>
complete(s"logon: shopid=$id and opr=$op")
}
~ (pathSuffix("logoff") & parameter('shopid.as[Int])){ id =>
complete(s"logoff: shopid=$id")
}
~ (pathSuffix("logsales") & parameters(
'shopid.as[Int],
'acct,
'dpt,
'code,
'qty.as[Int],
'price.as[Int]
)){ (id,acct,dpt,code,qty,price) =>
complete(s"logsales: shopid=$id,$acct,$dpt,$code,$qty,$price")
}
~ (pathSuffix("subtotal") & parameters('shopid.as[Int],'level)){ (id,l) =>
complete(s"subtotal: shopid=$id, level=$l")
}
)
}
用browser来测试：
http://192.168.11.189:8011/pos-on-cloud/logsales?shopid=1101&acct=001&dpt=01&code=978111&qty=3&price=1200
logsales: shopid=1101,001,01,978111,3,1200
没错，解析正确！