DateFormat parse method usage

Question

Hi all,
I am using the following code to parse the date String object to Date Object -
======================================================================
if(dateString == null || dateString.trim().equals(""))
return null;
DateFormat dateFormatter = DateFormat.getDateInstance(DateFormat.SHORT,
Locale.getDefault());
Date d = null;
try
dateFormatter.setLenient(false);
d = dateFormatter.parse(dateString);
catch(ParseException pe)
e.printStackTrace();
=================================================================
This code works perfectly for all formats of String objects I give except for the format - "12/12/12/1" in which case it converts to following date object -
"Wed Dec 12 00:00:00 IST 2012" although its an invalid date String.
Please let me know how I could have correct validation done in such cases or if this is the right behavior for DateFormat class.
Thanks in advance!!

Answer 1

I'm not going to comment on how exactly the parse method does its business, but I can suggest you use a regex pattern to validate the input you will send the parse method.
Here is some info from the CodeProject website on date validation(Note that this is aimed at .NET - but regex works the same in Java as it does in .NET [i think]):
Dates: As with numbers, we need two validators: a key-press validator, and a completion validator. The key-press validator can be pretty simple, if we limit how our user enters the date. Let’s say that we want to validate for the U.S. date format mm/dd/yyyy. Here is a validator that will do that:
^([0-9]|/)*$
The regex reads: “Match any string that contains a sequence of zero or more characters, where each character is either a digit or a slash.” This validator will give the user immediate feedback if they enter an invalid character, such as an ‘a’.
Copy that regex to Regex Tester and give it a try. Note that the validation fails if the user enters dashes, instead of slashes, between the parts of the date. How could we increase the flexibility of our regex to accommodate dashes? Think about the question for a minute before moving on.
All we need to do is add a dash to the alternates group:
^([0-9]|/|-)*$
We could add other alternates to make the regex as flexible as it needs to be.
The completion validator does a final check to determine whether the input matches a complete date pattern:
^[0-2]?[1-9](/|-)[0-3]?[0-9](/|-)[1-2][0-9][0-9][0-9]$
The regex reads as follows: "Match any string that conforms to this pattern: The first character can be a 0, 1, or 2, and it may be omitted. The second character can be any number and is required. The next character can be a slash or a dash, and is required…” And so on. This regex differs from the ones we used before in that it specifies each character of the pattern—the pattern is more of a template than a formula.
Note the first character of the regex: ‘[0-2]’. This character points out that we can limit allowable digits to less than the full set. We can also expand them; for example, ‘[0-9A-F]’ would allow any hexadecimal digit. In fact, we can use this structure, known as a character class, to specify any set of characters we want. For example, the character class ‘[A-Z]’ allows capital letters, and ‘[A-Za-z]’ allows upper or lower-case letters.
Our date regex also points out some of the limitations of regex validation. Paste the date regex shown into Regex Tester and try out some dates. The regex does a pretty good job with run-of-the-mill dates, but it allows some patently invalid ones, such as ‘29/29/2006’, or ‘12/39/2006'. The regex is clearly not ‘bulletproof’.
We could beef up the regular expression with additional features to catch these invalid dates, but it may be simpler to simply use a bit of .NET in the completion validator:
bool isValid = DateTime.TryParse(dateString, out dummy);
We gain the additional benefit that .NET will check the date for leap year validity, and so on. As always, the choice comes down to: What is simpler? What is faster? What is more easily understood? In my shop, we use a regex for the key-press validator, and DateTime.TryParse() for the completion validator.
Oh - and there is another regex validator:
^[0-9]{4}-(((0[13578]|(10|12))-(0[1-9]|[1-2][0-9]|3[0-1]))|(02-(0[1-9]|[1-2][0-9]))|((0[469]|11)-(0[1-9]|[1-2][0-9]|30)))$
which matches the yyyy-mm-dd date format and also validates month and number of days in a month. Could be improved as currently all leap year dates (yyyy-02-29) will validate.
Sorry if I couldn't be of more help...
Edited by: JoKiLlSyA on Oct 9, 2008 11:22 PM