Parse java.time trying multiple patterns

Question

We have a library where users can pass in dates in multiple formats. They follow the ISO but are abbreviated at times. So we get things like "19-3-12" and "2019-03-12T13:12:45.1234" where the fractional seconds can be 1 - 7 digits long. It's a very large number of combinations. DateTimeFormatter.parseBest doesn't work because it won't accept "yy-m-d" for a local date. The solutions here won't work because it assumes we know the pattern - we don't. And telling people to get their string formats "correct" won't work as there's a ton of existing data (these are mostly in XML & JSON files). My question is, how can I parse strings coming in in these various pattersn without have to try 15 different explicit patterns? Or even better, is there some way to parse a string and it will try everything possible and return a Temporal object if the string makes sense for any date[time]? JavaScript questions and answers, JavaScript questions pdf, JavaScript question bank, JavaScript questions and answers pdf, mcq on JavaScript pdf, JavaScript questions and solutions, JavaScript mcq Test , Interview JavaScript questions, JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)

Answer 1

Without a full specification it is hard to give a precise recommendation. The techniques generally used for variable formats include: Trying a number of known formats in turn. Optional parts in the format pattern. DateTimeFormatterBuilder.parseDefaulting() for parts that may be absent from the parsed string. As you are aware, parseBest. I am assuming that y-M-d always come in this order (never M-d-y or d-M-y, for example). 19-3-12 conflicts with ISO 8601 since the standard requires (at least) 4 digit year and 2 digit month. A challenge with 2-digit year is guessing the century: is this 1919 or 2019 or might it be 2119? The good news: presence and absence of seconds and varying number of fractional digits are all built-in and pose no problem. From what you have told us it seems to me that the following is a fair shot. DateTimeFormatter formatter = new DateTimeFormatterBuilder() .appendPattern("[uuuu][uu]-M-d") .optionalStart() .appendLiteral('T') .append(DateTimeFormatter.ISO_LOCAL_TIME) .optionalEnd() .toFormatter(); TemporalAccessor dt = formatter.parseBest("19-3-12", LocalDateTime::from, LocalDate::from); System.out.println(dt.getClass()); System.out.println(dt); Output: class java.time.LocalDate 2019-03-12 I figure that it should work with the variations of formats that you describe. Let’s just try your other example: dt = formatter.parseBest( "2019-03-12T13:12:45.1234", LocalDateTime::from, LocalDate::from); System.out.println(dt.getClass()); System.out.println(dt); class java.time.LocalDateTime 2019-03-12T13:12:45.123400 To control the interpretation of 2-digit year you may use one of the overloaded variants of DateTimeFormatterBuilder.appendValueReduced(). I recommend that you consider a range check on top of it.