使用Scala Option验证命令行参数

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)

Answer 1

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

Answer 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
  }
}