在Play2.5 / scala控制器中处理异常

Question

I would like to catch exception and redirect to a custom page in the following code. However, exceptions are not caught/seen.

def addItemWithParts(item: Item, parts: Seq[String]): Future[Int] = {
  ... // May throw exceptions
}

def handleAddItem = auth.SecuredAction.async { implicit request =>
  itemForm.bindFromRequest.fold(
    formWithErrors => {
      Future.successful(
        Redirect(controllers.www.routes.ItemController.startAddItem()).flashing(
          "error" -> "Bad item add input"
        )
      )
    },
    item => {
      for {
        ue <- usersService.findUserEntryByEmail(request.identity.email)
      } yield ue match {
        case Some(ue) =>
          val itemObj = Item(item.name, item.description, ue.companyId)
          val xx = itemsService.addItemWithParts(itemObj, Seq(item.parts)) <-- want to catch exception thrown by this function
          /*
           * COMMENTED CODE PRINTS EXCEPTION ON CONSOLE, BUT DONT KNOW HOW TO REDIRECT/OK...
          xx onComplete {
            case Success(x) => {
              println("Added ITEM: " + x)
              Redirect(controllers.www.routes.Dashboard.dashboard)
            }
            case Failure(exp) => {
              println("Exception while adding ITEM: " + exp)
              Ok("Got exception: " + exp)
            }
          }
          */
          Redirect(controllers.www.routes.Dashboard.dashboard) // +++
        case None =>
          Ok("Bad")
      }
    }
  )
}

I thought I can do Redirect() from onComplete success instead of at line marked "+++" but I get this compilation error:

type mismatch;
[error]  found   : Unit
[error]  required: play.api.mvc.Result
[error]           case Some(ue) =>
[error]                         ^
[error] one error found

I checked play documentation, it talks about adding onServerError to ErrorHandler (centralized) but I want to know what I am missing in doing it this way.

I am still learning Scala, any help is deeply appreciated.

Answer 1

onComplete returns Unit . You can do only side effecting operations using onComplete .

Use map , flatMap for composing and building new computations. Use recover and recoverWith to handle exceptions and return something on exceptions.

here is how you can do this

val result = 
for {
 ueOpt <- usersService.findUserEntryByEmail(request.identity.email)
 result <- ueOpt match {
            case Some(ue) =>

               val itemObj = Item(item.name, item.description, ue.companyId)
               val foo = itemsService.addItemWithParts(itemObj, Seq(item.parts))

              foo.map { value =>
                Redirect(controllers.www.routes.Dashboard.dashboard)
              }.recover { case th =>
                InternalServerError("bad things happen in life.")
              }

            case None => Future.successful(BadRequest("no item found"))
          }
} yield result

Future provides methods like map , flatMap to build new computations with result of the current future. Also future provides recover and recoverWith to build computations when current future throws exceptions.

def bar: Future[Int] = ???

bar.map { intValue =>
  //doSomething
}.recover {
  case ex: SQLException => //return some value
  case _ => //ignore other exceptions and return default value
}