Scala/Lift check if date is correctly formatted

Question

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 reg

Answer 1

I wouldn't use a regex, but SimpleDateFormat (which isn't that simple, as we will see).

A regular expression which handles to allow 28 and 30 as day, but not 38, different month-lengths and leap years, might be an interesting challenge, but not for real world code.

val df = new java.text.SimpleDateFormat ("dd/MM/yyyy")

(I assume M as in big Month, not m as in small minute).

Now, let's start with an error:

scala> df.parse ("09/13/2001")                                
res255: java.util.Date = Wed Jan 09 00:00:00 CET 2002

hoppla - it is very tolerant, and wraps months around to the next year. But we can get it with a second formatting process:

scala> val sInput = "13/09/2001"
sInput: java.lang.String = 13/09/2001

scala> sInput.equals (df.format (df.parse (sInput))) 
res259: Boolean = true

scala> val sInput = "09/13/2001"                     
sInput: java.lang.String = 09/13/2001

scala> sInput.equals (df.format (df.parse (sInput))) 
res260: Boolean = false

I hope you aren't bound to regex, and can use it.