Java正则表达式验证日期范围

Question

I having problems to generate a regex for a range of dates. For example this range [2015-11-17, 2017-10-05] , How can I do? to validate if having a date belogns to that range using regex.

And second question if is possible to have a generic regex which I can use for several range of date, only replacing few values in the regex with the new ranges I have, and the regex continues validating a range of dates , but with the new ranges. Thanks in advance for help =)

Answer 1

Do not use Regex

As the comments state, Regex is not appropriate for a range of dates, nor any span of time. Regex is intended to be “dumb” in the sense of looking only at the syntax of the text not the semantics (the meaning).

java.time

Use the java.time framework built into Java 8 and later.

Parse your strings into LocalDate objects.

LocalDate start = LocalDate.parse( "2015-11-17" );

Compare by calling the isEqual, isBefore, and isAfter methods.

Note that we commonly use the Half-Open approach in date-time work where the beginning is inclusive while the ending is exclusive.

These issues are covered already in many other Questions and Answers on Stack Overflow. So I have abbreviated my discussion here.

Answer 2

Just for completeness: You can actually use regular expressions to recognize any finite set of strings, such as a specific date range, however it would be more of an academic exercise than an actual recommended usage. However , if you happen to be programming some arcane hardware it could actually be necessary.

Assuming the input is always a valid date in the given format, the regex for your example could consist of:

2015-0[1-9].* - 2015 January to September

2015-10.* - 2015 October

2015-11-0[1-9] - 2015 November 1 to 9

2015-11-1[0-7] - 2015 November 10 to 17

2016.* - all dates of 2016

Add analogously for 2017, make a disjunction using | (a|b|c|...), apply escaping of the regex implementation you use and then you have your date checker. If the input is not guaranteed to be a valid date it gets a bit more complicated but is still possible.