Dynamic regex for date formats

Question

Is there an existing solution for dynamically creating regular expressions from a given date format template? The supported date format format does not matter (Joda DateTimeFormat, java.text.SimpleDateTimeFormat or others).

i.e. for a specific date and time format (for example, "dd / MM / yyyy hh: mm"), it will generate the appropriate regular expression to match the time dates in the specified formats.

Answer 1

I assume that you have a limited alphabet from which your temporary formats can be created. This means that "HH" will always be “hours” on a 24-hour clock, "dd" always a day with a start zero, etc.

Due to the consistent nature of the time format, you can try tokenize a string of the format "dd/mm/yyyy HH:nn" into the array ["dd", "/", "mm", "/", "yyyy", " ", "HH", ":", "nn"] . Then go and form a template string from this array, replacing "HH" with "([01][0-9]|2[0-3])" and so on. Predesign these template atoms into a lookup table / array. All parts of your array that are not in the lookup table are literals. Select them according to the rules of regular expressions and add them to the template line.

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EDIT: as a side effect of a regular expression solution, when you put all the "regular expressions" of your lookup table in parsers and track their order in a given format string, you can use subheadings to extract the necessary components from the match and feed them into a function CreateDate, thereby completely skipping the ParseDate part.

Answer 2

If you are looking for a basic date check. this code matches this data.

 \b(0?[1-9]|[12][0-9]|3[01])[- /.](0?[1-9]|1[012])[- /.](19|20)?[0-9]{2}\b 10/07/2008 10.07.2008 1-01/2008 10/07/08 10.07.2008 1-01/08 

Code via regexbuddy

Answer 3

SimpleDateFormat already does this with the parse() method.

If you need to parse multiple dates from a single line, start with a regular expression (even if it matches too condescendingly) and use parse() for all possible matches found by the regular expression.

Answer 4

Below is the js / jQuery code for dynamically generating a regular expression for the date format Only, not for the date Time (the development version has not yet been fully tested.)

Date format must be in "DMY"

eg.
DD-MM-GG,
DD-MM-YYYY,
YYYY-MM-DD,
YYYY-DD-MM,
MM-DD-YYYY,
MM-DD-GG,
DD / MM / YY,
DD / MM / YYYY,
YYYY / MM / DD,
YYYY / DD / MM,
MM / DD / YYYY,
MM / DD / YY
Or other formats, but created with the symbol [DMY]

 var dateFormat = "DD-MM-YYYY"; var order = []; var position = {"D":dateFormat.search('D'),"M":dateFormat.search('M'),"Y":dateFormat.search('Y')}; var count = {"D":dateFormat.split("D").length - 1,"M":dateFormat.split("M").length - 1,"Y":dateFormat.split("Y").length - 1}; var seprator =''; for(var i=0; i<dateFormat.length; i++){ if(["Y","M","D"].indexOf(dateFormat.charAt(i))<0){ seprator = dateFormat.charAt(i); }else{ if(order.indexOf(dateFormat.charAt(i)) <0 ){ order.push(dateFormat.charAt(i)); } } } var regEx = "^"; $(order).each(function(ok,ov){ regEx += '(\d{'+count[ov]+'})'+seprator; }); regEx = regEx.substr(0,(regEx.length)-1); regEx +="$"; var re = new RegExp(regEx); console.log(re); 

NOTE. No validation checks for months / days for example. the month should be 01-12 or the date should be 01-31