How to "override" an exception in scala?-CodePudding

so I have a method which already has a try block that throws ExceptionA. Now I need to put another try block where this method is being called and needs to throw an exception with some added details. Something like this:

method inner():
    try{
    //some logic
    } catch {
    throw new ExceptionA("exceptionA occurred")
    }

method outer():
    identifier = fromSomeDBCallPrivateToOuter()
    try{
    inner()
    } catch {
    // now either 
    // throw new Exception("Error with identifier"   identifier)
    // or
    // append identifier to thrown error from inner() 
    }

Can someone please provide any insight or suggestion on how to do this in Scala? Thanks in advance!

CodePudding user response：

What you have in your snippet would work as written (if you correct the syntax), with a caveat, that exceptions are immutable (and even they weren't, it's still not a good idea to mutate them), so, instead of "appending" to exception, you'd need to create a new one, and set the original as cause.

It is more idiomatic in scala though to use Try monad instead of the "procedural" try/catch blocks. Something like this:

     case class ExceptionB(id: String, original: ExceptionA) 
         extends Exception(s"Badness happened with id $id", original)
     def outer(): Try[ReturnType] = 
       val id = getId()
       Try {
         inner 
       } recover { 
         case e: ExceptionA if iWannaNewException => throw new Exception(s"Id: id")
         case e: ExceptionA => throw ExceptionB(id, e)
      }

CodePudding user response：

You can also use Either structure. This structure can return Right(value) if function completes without error or Left(message) containing information about error. You can adapt your code like below one:

def inner(): Either[String, Int] = {
  if (checkSomeStuff()) Left("Cannot assigne identifier")
  else Right(doSomeStuff())
}

def outer(): Either[String, Int] = {
  inner() match {
    case Left(error)  => {
      println("There is an error: "   error) 
     // you can also throw new Exception(s"Some info about $error") here
    }
    case Right(identifier) => {
      println("Identifier : "   identifier) 
      doSomeStuffWithId()  // do some staff for id
    }
  }
}

If you want to use Exceptions you need to choose who will handle the error case (in the inner or in the outer function).