Handling Exceptions in Play Framework

Question

I would like to have some suggestions on exception handling mechanism. I currently have the traditional try catch finally but I understand that it is not functional in style. So what is the best functional way of handling exceptions. I tried looking into the Scala arm, but it is just a functional wrapper around the try catch finally I suppose! Suggestions? Here is my Play controller where I want to handle the exception that is thrown and send a plain String back to the client!

def testmethod = Action(parse.maxLength(10 * 1024 * 1024, parser = parse.anyContent)) { implicit request =>
    request.body match {
      case Left(_) => EntityTooLarge
      case Right(body) => {
        println(request.headers.toSimpleMap)
        val js = // Get the value from the request!!!

        val resultJsonfut = scala.concurrent.Future { longRunningProcess(js) }

        Async {
          if(request.headers.toSimpleMap.exists(_ == (ACCEPT_ENCODING, "gzip"))) {
            resultJsonfut.map(s => {
              val bytePayload = getBytePayload(s) // How to handle exceptions thrown by getBytePayLoad????
              Ok(bytePayload)
            })
          } else {
            resultJsonfut.map(s => Ok(s))
          }
        }
      }
    }
  }

Peter · Accepted Answer · 2014-02-25T13:36:16.883

You could create a method that you would call to handle exception inside your Actions, this method would look something like this:

def withExceptionHandling(f: => Result)(implicit request: Request[AnyContent]): Result = 
    try{ f }catch{ case e: Exception => InternalServerError("Something bad happened")}

And then you would use it like this:

def testmethod = Action(parse.maxLength(10 * 1024 * 1024, parser = parse.anyContent)) { implicit request => 
  withExceptionHandling {
    request.body match {
      case Left(_) => EntityTooLarge
      case Right(body) => {
        println(request.headers.toSimpleMap)
        val js = // Get the value from the request!!!

        val resultJsonfut = scala.concurrent.Future { longRunningProcess(js) }

        Async {
          if(request.headers.toSimpleMap.exists(_ == (ACCEPT_ENCODING, "gzip"))) {
            resultJsonfut.map(s => {
              val bytePayload = getBytePayload(s) // How to handle exceptions thrown by getBytePayLoad????
              Ok(bytePayload)
            })
          } else {
            resultJsonfut.map(s => Ok(s))
          }
        }
      }
    }
  }
}

This will prevent you from explicitly trying and catching on each of your Actions.

That sounds like an idea. But how do you handle closing of streams that we normally do in the finally block? — joesan, Feb 25 '14 at 13:37
Check this question, seems it handles exactly what you needs in terms of closing streams/releasing resources... http://stackoverflow.com/questions/8865754/scala-finally-block-closing-flushing-resource — Peter, Feb 25 '14 at 13:49

Handling Exceptions in Play Framework

1 Answers1