如何处理playframework中的异常2异步块(scala)

Question

我的控制器动作代码如下所示:

  def addIngredient() = Action { implicit request =>
    val boundForm = ingredientForm.bindFromRequest
    boundForm.fold(
      formWithErrors => BadRequest(views.html.Admin.index(formWithErrors)),
      value => {
        Async {
          val created = Service.addIngredient(value.name, value.description)
          created map { ingredient =>
            Redirect(routes.Admin.index()).flashing("success" -> "Ingredient '%s' added".format(ingredient.name))
          }

          // TODO on exception do the following
          // BadRequest(views.html.Admin.index(boundForm.copy(errors = Seq(FormError("", ex.getMessage())))))
        }
      })
  }

我的Service.addIngredient(...)返回一个Promise [Ingredient],但也可以抛出一个自定义的ValidationException.抛出此异常时,我想返回注释代码.

目前页面呈现为500,在日志中我有:

玩 - 等待承诺,但得到一个错误:名称'test'的成分已经存在.services.ValidationException:名称为'test'的成分已存在.

两个问题:

• 从我的服务返回此异常是一个坏主意,是否有更好/更多的scala方法来处理这种情况？
• 我如何捕获异常？

Answer 1

我想说，纯函数式方法是使用可以保存有效和错误状态的类型。

为此，您可以使用scalaz验证表单

但是，如果不需要 scalaz 提供的更多内容（您会 ^^），您可以使用非常简单的东西，使用 aPromise[Either[String, Ingredient]]作为结果及其fold在异步块中的方法。即在承诺被赎回时以及在赎回的东西上map转换价值。fold

优点 => 没有例外 => 每件事都经过键入检查:-)

编辑

它可能需要更多信息，这里有两个选项：try catch，感谢@kheraud）和Either。没放Validation，需要的话问我。对象应用程序扩展控制器{

  def index = Action {
    Ok(views.html.index("Your new application is ready."))
  }

  //Using Try Catch
  //  What was missing was the wrapping of the BadRequest into a Promise since the Async
  //    is requiring such result. That's done using Promise.pure
  def test1 = Async {
    try {
      val created = Promise.pure(new {val name:String = "myname"})
      created map { stuff =>
        Redirect(routes.Application.index()).flashing("success" -> "Stuff '%s' show".format(stuff.name))
      }
    } catch {
      case _ => {
        Promise.pure(Redirect(routes.Application.index()).flashing("error" -> "an error occurred man"))
      }
    }
  }


  //Using Either (kind of Validation)
  //  on the Left side => a success value with a name
  val success = Left(new {val name:String = "myname"})
  //  on the Right side the exception message (could be an Exception instance however => to keep the stack)
  val fail = Right("Bang bang!")

  // How to use that
  //   I simulate your service using Promise.pure that wraps the Either result
  //    so the return type of service should be Promise[Either[{val name:String}, String]] in this exemple
  //   Then while mapping (that is create a Promise around the convert content), we folds to create the right Result (Redirect in this case).
  // the good point => completely compiled time checked ! and no wrapping with pure for the error case.
  def test2(trySuccess:Boolean) = Async {
      val created = Promise.pure(if (trySuccess) success else fail)
      created map { stuff /* the either */ =>
        stuff.fold(
          /*success case*/s => Redirect(routes.Application.index()).flashing("success" -> "Stuff '%s' show".format(s.name)),
          /*the error case*/f => Redirect(routes.Application.index()).flashing("error" -> f)
        )

      }

  }

}