how to catch all the errors in any scalatra action?

Question

I am using scalatra to "export" a MongoDB data to JSon, my actions are very simple, like:

   get("/") {
      val title = db.get_collection("main", "api", "title")
      send_json(title)
    }

I want to send a HTTP error and a text if something go wrong, on the other side it will be converted to something meaninful to the user. So the method becames:

   get("/") {
     try {
      val title = db.get_collection("main", "api", "title")
      send_json(title)
     } catch {
      case e:java.util.NoSuchElementException => send_error("DB malformed", InternalError)
      case e:com.mongodb.MongoException => send_error("Can not connect to MongoDB", InternalError)
      case e => send_error("Internal Error", InternalError)
    }
  }

The try catch is bigger that the actual method and I need to do this for every method, the class become at first sight an ugly collection of try catch. There is any way to avoid or minimize the bad looking and distracting try catch all over the code? I am new to Scala (and Java BTW) so I guess I am missing something.

I dont want the DB object to send JSON, so having the try catch on the db.get_collection method is not an option.

knub · Answer 1 · 2014-09-05T17:09:01.910

46

There's a special route handler for this:

error {
  case e: Throwable => {
    redirect("/")
  }
}

By changing the case statement you can switch on the error type.

edited Sep 05 '14 at 17:09

answered Feb 06 '13 at 15:13

knub

3,892
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1

This is the idiomatic method for handling errors in Scalatra, though it's missing from the documentation. – afternoon Mar 14 '13 at 16:17

Daniel C. Sobral · Accepted Answer · 2012-02-29T15:59:22.453

6

Well, I don't know Scalatra enough, but the catch block is a partial function, so you could do something like this:

val errorHandling: PartialFunction[Throwable, Unit] = {
  case e:java.util.NoSuchElementException => send_error("DB malformed", InternalError)
  case e:com.mongodb.MongoException => send_error("Can not connect to MongoDB", InternalError)
  case e => send_error("Internal Error", InternalError)
}

get("/") {
  try {
   val title = db.get_collection("main", "api", "title")
   send_json(title)
  } catch errorHandling
}

edited Feb 29 '12 at 15:59

answered Feb 28 '12 at 14:56

Daniel C. Sobral

295,120
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my final solution was: `val errorHandling: PartialFunction[Throwable, Unit] = {` If I use errorHandler, I got an error about that name to need to be override. It also seemed to need java.lang.Throwable instead of Exception – user1216071 Feb 29 '12 at 04:04
@user1216071 Ok, I fixed the code accordingly, so others won't have to figure it out (if they happen to miss your comment). – Daniel C. Sobral Feb 29 '12 at 15:59

how to catch all the errors in any scalatra action?

2 Answers2