CODEWITHSUNDEEP
scala
j3d
j3d

Reputation: 9724

Scala: Error handling and exception matching

Given the following custom Exception ...

trait ServiceException extends RuntimeException {

  val errorCode: Int
}

object ServiceException {

  def apply(
    message: String, _errorCode: Int
  ): ServiceException = new RuntimeException(message) with ServiceException {
    val errorCode: Int = _errorCode
  }

  def apply(
    message: String, cause: Throwable, _errorCode: Int
  ): ServiceException = new RuntimeException(message, cause) with ServiceException {
    val errorCode: Int = _errorCode
  }
}

... and the following method returning a Future ...

myService.doSomethingAndReturnFuture.map {
  ...
}.recover {
  case ServiceException(5) =>
    Logger.debug("Error 5")
// this does not work
// case e: ServiceException(5) =>
//   Logger.debug(s"Error 5: ${e.getMessage}")
  case NonFatal(e) =>
    Logger.error("error doing something", e)
}

... how do I get the error message from ServiceException?

Upvotes: 1

Views: 4552

Answers (2)

som-snytt
som-snytt

Reputation: 39577

People like case classes.

This does not exactly align with your givens, but for example:

scala> trait ServiceException { _: RuntimeException => def errorCode: Int }
defined trait ServiceException

scala> case class MyX(errorCode: Int, msg: String, cause: Exception = null) extends RuntimeException(msg, cause) with ServiceException
defined class MyX

scala> def i: Int = throw MyX(42, "Help!")
i: Int

scala> import concurrent._ ; import ExecutionContext.Implicits._
import concurrent._
import ExecutionContext.Implicits._

scala> Future(i) recover { case MyX(code, m, err) => println(m) ; -1 }
res11: scala.concurrent.Future[Int] = scala.concurrent.impl.Promise$DefaultPromise@7d17ee50

scala> Help!

scala> .value
res12: Option[scala.util.Try[Int]] = Some(Success(-1))

Upvotes: 1

Kigyo
Kigyo

Reputation: 5768

You will need an unapply for your described match to work, which should be defined in the companion object.

object ServiceException {

   //... apply methods

  def unapply(ex: ServiceException) = Some(ex.errorCode)  
}

And then you can match.

recover {
  case se@ServiceException(5) => println(s"Error 5: ${se.getMessage}")
  case _ => println("Some other error")
}

You could also include the message in the unapply.

def unapply(ex: ServiceException) = Some((ex.errorCode, ex.getMessage))

and then match like this:

recover {
  case ServiceException(5, msg) => println(s"Error 5: $msg")
  case _ => println("Some other error")
}

As an alternative you can also do it without the unapply. Then it could look like:

recover {
  case se: ServiceException if se.errorCode == 5 => println(s"Error 5: ${se.getMessage}")
  case _ => println("Some other error")
}

Upvotes: 5

Related Questions