播放没有依赖注入的框架？

Question

不解释为什么，假设有人想要一个老式的 Play Framework Web 服务，不想使用依赖注入，也不想依赖 Google 的 Guice。 Play 2.8.x 还可以吗？

api documentation 以及当前的 Play 示例将其推荐为“典型”HomeController.scala：

package controllers
import javax.inject._
import play.api.mvc._
class HomeController @Inject() (val controllerComponents: ControllerComponents) extends BaseController {
  def index = Action {
    Ok("It works!")
  }
}

我想要的代码是相同的，但没有 @Inject()（类似于我上次在 2016 年使用 Play 2.4.0 时）？以前我的代码是这样的：

package controllers
import play.api.mvc.{Action, AnyContent, Controller}
object TestController {
  def index:Action[AnyContent] = Action {
    Ok("It used to work.")
  }
}

控制台：

[info] Compiling 1 Scala source to /Volumes/.../play-scala-seed/target/scala-2.13/classes ...
[error] p.a.h.DefaultHttpErrorHandler - 

! @7ef69nl6l - Internal server error, for (GET) [/test/] ->

play.api.UnexpectedException: Unexpected exception[CreationException: Unable to create injector, see the following errors:

1) Could not find a suitable constructor in controllers.TestController. Classes must have either one (and only one) constructor annotated with @Inject or a zero-argument constructor that is not private.
  at controllers.TestController.class(TestController.scala:3)
  while locating controllers.TestController
    for the 4th parameter of router.Routes.<init>(Routes.scala:33)
  at play.api.inject.RoutesProvider$.bindingsFromConfiguration(BuiltinModule.scala:137):
Binding(class router.Routes to self) (via modules: com.google.inject.util.Modules$OverrideModule -> play.api.inject.guice.GuiceableModuleConversions$$anon$4)

1 error]
    at play.core.server.DevServerStart$$anon$1.reload(DevServerStart.scala:210)
    at play.core.server.DevServerStart$$anon$1.get(DevServerStart.scala:141)
    at play.core.server.AkkaHttpServer.handleRequest(AkkaHttpServer.scala:296)
    at play.core.server.AkkaHttpServer.$anonfun$createServerBinding$1(AkkaHttpServer.scala:186)
    at akka.stream.impl.fusing.MapAsync$$anon$30.onPush(Ops.scala:1261)
    at akka.stream.impl.fusing.GraphInterpreter.processPush(GraphInterpreter.scala:541)
    at akka.stream.impl.fusing.GraphInterpreter.execute(GraphInterpreter.scala:423)
    at akka.stream.impl.fusing.GraphInterpreterShell.runBatch(ActorGraphInterpreter.scala:624)
    at akka.stream.impl.fusing.GraphInterpreterShell$AsyncInput.execute(ActorGraphInterpreter.scala:501)
    at akka.stream.impl.fusing.GraphInterpreterShell.processEvent(ActorGraphInterpreter.scala:599)
Caused by: com.google.inject.CreationException: Unable to create injector, see the following errors:

1) Could not find a suitable constructor in controllers.TestController. Classes must have either one (and only one) constructor annotated with @Inject or a zero-argument constructor that is not private.
  at controllers.TestController.class(TestController.scala:3)
  while locating controllers.TestController
    for the 4th parameter of router.Routes.<init>(Routes.scala:33)
  at play.api.inject.RoutesProvider$.bindingsFromConfiguration(BuiltinModule.scala:137):
Binding(class router.Routes to self) (via modules: com.google.inject.util.Modules$OverrideModule -> play.api.inject.guice.GuiceableModuleConversions$$anon$4)

1 error
    at com.google.inject.internal.Errors.throwCreationExceptionIfErrorsExist(Errors.java:543)
    at com.google.inject.internal.InternalInjectorCreator.initializeStatically(InternalInjectorCreator.java:159)
    at com.google.inject.internal.InternalInjectorCreator.build(InternalInjectorCreator.java:106)
    at com.google.inject.Guice.createInjector(Guice.java:87)
    at com.google.inject.Guice.createInjector(Guice.java:78)
    at play.api.inject.guice.GuiceBuilder.injector(GuiceInjectorBuilder.scala:200)
    at play.api.inject.guice.GuiceApplicationBuilder.build(GuiceApplicationBuilder.scala:155)
    at play.api.inject.guice.GuiceApplicationLoader.load(GuiceApplicationLoader.scala:21)
    at play.core.server.DevServerStart$$anon$1.$anonfun$reload$3(DevServerStart.scala:189)
    at play.utils.Threads$.withContextClassLoader(Threads.scala:21)

有没有一个简单的解决办法来保持老派——不用去here？

我承认但不完全理解https://www.playframework.com/documentation/2.4.x/Migration24。我认为我的问题与在 2.7 中删除的静态路由有关。

Answer 1

我的声誉不允许我通过Mario Galic 对answer 发表评论，但您可以使用BuiltInComponentsFromContext 提供的“正确”（非测试）controllerComponents 轻松修改他的示例.

整个例子看起来像

class HomeController(override protected val controllerComponents: ControllerComponents)
  extends BaseController {
  def index = Action { Ok("It works!") }
}

class MyApplicationLoader extends ApplicationLoader {
  def load(context: ApplicationLoader.Context): Application = {
    new BuiltInComponentsFromContext(context) {
      lazy val homeController = HomeController(controllerComponents)
      override lazy val router: Router = Routes(httpErrorHandler, homeController)
    }.application
  }
}

Answer 2

回答@kujosHeist 关于Java 中一个等效示例的评论。这似乎对我有用（遵循Play docs）：

package controllers;

import play.mvc.Controller;
import play.mvc.Result;

public class HomeController extends Controller {
    public Result index() {
        return ok("It works!");
    }
}

public class MyApplicationLoader implements ApplicationLoader {

    @Override
    public Application load(Context context) {
        return new MyComponents(context).application();
    }
}


class MyComponents extends BuiltInComponentsFromContext implements HttpFiltersComponents, AssetsComponents {

    public MyComponents(ApplicationLoader.Context context) {
        super(context);
    }

    @Override
    public Router router() {
        HomeController homeController = new HomeController();
        Assets assets = new Assets(scalaHttpErrorHandler(), assetsMetadata());
        return new router.Routes(scalaHttpErrorHandler(), homeController, assets).asJava();
    }

}

您可能想要定义诸如错误处理程序不同，但这可能是大致的结构。

Answer 3

确实StaticRoutesGenerator 一直是removed，它需要将控制器作为单例对象。也许使用compile time dependency injection，例如here，可能会让你更接近你以前的习惯，但是ControllerComponents仍然需要注入。从技术上讲，将play-test 放在Compile 类路径上并像这样使用stubControllerComponents 可能会做一些不明智的事情

class HomeController extends BaseController {
  def index = Action { Ok("It works!") }

  override protected def controllerComponents: ControllerComponents = 
     play.api.test.Helpers.stubControllerComponents()
}

以及对应的最小ApplicationLoader

class MyApplicationLoader extends ApplicationLoader {
  def load(context: ApplicationLoader.Context): Application = {
    new BuiltInComponentsFromContext(context) {
      override def httpFilters: Seq[EssentialFilter] = Nil
      lazy val homeController = new _root_.controllers.HomeController
      lazy val router: Router = new _root_.router.Routes(httpErrorHandler, homeController)
    }.application
  }
}

这样HomeController虽然仍然是一个类，但现在完全是硬连线的，并且在ApplicationLoader中只创建了它的一个实例。

就我个人而言，我建议不要使用这种恶作剧，并相信 arguments 为什么 Play 会放弃单例，例如可测试性、thread-safety 等。