I have a date input box in my lift application, and I want to check that a user-entered date is in correct format: dd/mm/yyyy.
How can I write a regex check for this in scala? I've looked at pattern matching examples - but that seems over-complicated.
PS: I don't have to use regex, any other alternatives are welcome!
SimpleDateFormat is ugly and (more disturbingly) non-thread-safe. If you try to simultaneously use the same instance in 2 or more threads then expect things to blow up in a most unpleasant fashion.
JodaTime is far nicer:
import org.joda.time.format._
val fmt = DateTimeFormat forPattern "dd/MM/yyyy"
val input = "12/05/2009"
val output = fmt parseDateTime input
If it throws an IllegalArgumentException, then the date wasn't valid.
As I suspect you'll want to know the actual date if it was valid, you may want to return an Option[DateTime], with None if it was invalid.
def parseDate(input: String) = try {
Some(fmt parseDateTime input)
} catch {
case e: IllegalArgumentException => None
}
Alternatively, use an Either to capture the actual exception if formatting wasn't possible:
def parseDate(input: String) = try {
Right(fmt parseDateTime input)
} catch {
case e: IllegalArgumentException => Left(e)
}
UPDATE
To then use the Either, you have two main tactics:
map one of the two sides:
parseDate(input).left map (_.getMessage)
//will convert the Either[IllegalArgumentException, DateTime]
//to an Either[String, DateTime]
fold it:
parseDate(input) fold (
_ => S.error(
"birthdate",
"Invalid date. Please enter date in the form dd/mm/yyyy."),
dt => successFunc(dt)
)
Of course, the two can be composed:
parseDate(input).left map (_.getMessage) fold (
errMsg => S.error("birthdate", errMsg), //if failure (Left by convention)
dt => successFunc(dt) //if success (Right by convention)
)