Using Scala Option to validate command line argument

Question

I am using Apache commons CLI for command line parsing in a Scala utility application. One of the arguments is a database port number (--port=) that overrides the default "5432" (for PostgreSQL). I am trying to use the Option class to assist in the validation. Here is the code I came up with. Is there a better way to do the validation?

val port = Option(commandLine.getOptionValue("port", "5432")) map {
  try {
    val value = Integer.parseInt(_)
    if (value < 1 || value > 65535) throw new NumberFormatException
    value
  } catch {
    case ex: NumberFormatException =>
      throw new
        IllegalArgumentException("the port argument must be a number between 1 and 65535")
  }
} get

The port number must be an integer between 1 and 65535, inclusive.

Would it be better to do this? Why or why not?

val port = Option(commandLine.getOptionValue("port")) map {
  try {
    val value = Integer.parseInt(_)
    if (value < 1 || value > 65535) throw new NumberFormatException
    value
  } catch {
    case ex: NumberFormatException =>
      throw new
        IllegalArgumentException("the port argument must be a number between 1 and 65535")
  }
} getOrElse(5432)

What I'm missing in the std lib is a method String => Option[Int]. — ziggystar
– ziggystar, Commented Sep 22, 2011 at 12:32
@ziggystar: If you can use Scalaz, it has a method parsent: String => Validation[NumberFormatException, Int]. Calling toOption on the validation will give you Option[Int]. — missingfaktor
– missingfaktor, Commented Sep 22, 2011 at 12:40

agilesteel · Accepted Answer · 2011-09-22 12:05:14Z

7

I admit I'm not 100% sure, what you want to be thrown in case something goes wrong, or if the 5432 is a default port for every wrong value, but here is what I would do:

def getPort(candidate: Option[String]) = candidate
   .map { _.toInt } // throws NumberFormatException
   .filter { v => v > 0 && v <= 65535 } // returns Option[Int]
   .getOrElse { throw new IllegalArgumentException("error message") } // return an Int or throws an exception

answered Sep 22, 2011 at 12:05

agilesteel

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3 Comments

Ralph Over a year ago

I initially had something similar (with the map(_.toInt)), but I did not want to have to duplicate the error message.

Ralph Over a year ago

I think the code should throw an exception if the port is illegal. It should only use 5432 if no port was provided.

agilesteel Over a year ago

Then you can define the given method with a default value: def getPort(candidate: Option[String] = Some("5432")) = ...

huynhjl · Accepted Answer · 2011-09-22 14:32:01Z

2

I guess it's a good time for me to explore Validation.

import scalaz._
import Scalaz._

val port = {
  def checkRange(port: Int): Validation[String, Int] = {
    if (port < 1 || port > 65535) "port not in [1-65535]".fail
    else port.success
  }
  commandLine.getOptionValue("port", "5432")
    .parseInt.flatMap(checkRange) match {
    case Failure(e) => throw new IllegalArgumentException(e.toString)
    case Success(port) => port
  }
}

answered Sep 22, 2011 at 14:32

huynhjl

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