Free Yourself from the Tyranny of Null

Catching.scala

try {
  Some(Integer.parseInt(header))
} catch {
  case e: NumberFormatException => None
}

ContrivedExample.scala

// The mb prefix stands for maybe
def contrivedExample(mbNumber: Option[Int]): Int = {
  val step1 = possiblyNumber.map(number => number + 5)
  val step2 = step1.filter(number => number > 0)
  step2.getOrElse(0)
}

ExpandedOut.scala

def getIntFromHeader(mbRequest: Option[Request], key: String): Option[Int] = {
  mbRequest.flatMap { request =>
    request.headers.flatMap { headers =>
      headers.get(key).flatMap {  header =>
        catching(classOf[NumberFormatException]).opt(Integer.parseInt(header))
      }
    }
  }
}

FlatMap.scala

val mbHeaders: Option[Map[String, String]] = // ...
val mbHeader = mbHeaders.flatMap(headers => headers.get(key))

RequestOption.java

class Request {
    // ...

    Option<Map<String, String>> headers;

    // ...
}

/**
 * @param request The request object to look in
 * @param headerName the header name to look for
 */
public Option<Integer> getIntFromHeader(Option<Request> request, String headerName) {
  if(request.isDefined && request.get().getHeaders.isDefined() {
    // Ideally our data structures would be returning Option rather than null
    Option<String> header = Option.fromNull(request.get().getHeaders().get().get(headerName));
    if(header.isDefined()) {
      try {
        return new Some<Integer>(Integer.parseInt(header.get()));
      } catch(Exception e) {
        return new None<Integer>();
      }
    }
  }
  return new None<Integer>();
}

RequestScala.scala

class Request {
  // ...

  val headers: Option[Map[String, String]]

  // ...
}

def getIntFromHeader(mbRequest: Option[Request], key: String): Option[Int] = for {
  request <- mbRequest
  headers <- request.headers
  header <- headers.get(key) //returns an option
  intVal <- catching(classOf[NumberFormatException]).opt(Integer.parseInt(header))
} yield {
  intVal
}