Convert Date to DateTime using Joda

Question

Is there a way to convert a date in the format "YYYY-MM-dd" to "YYYY-MM-dd HH:mm:ss" using Joda?

Eg: "2016-01-21" to "2016-01-21 00:00:00"

Answer 1

Use DateTimeFormat class from Joda API. It helps you to format the date to the formatting of your choice. You can simply provide the format you want, like in this case you want "YYYY-MM-dd HH:mm:ss". The code below works with JodaTime 2.0 and above.

DateTime date = DateTime.parse("2016-01-21", DateTimeFormat.forPattern("YYYY-MM-dd HH:mm:ss"));

There are two things in play here, first we need to parse the existing string into a DateTime object, which is done via the parse method, it also allows an additional argument, to convert the output into a different format. The longer but easier to understand implementation is given below.

DateTime date = DateTime.parse("2016-01-21");
DateTimeFormatter formatter = DateTimeFormat.forPattern("YYYY-MM-dd HH:mm:ss");
date  = formatter.parseDateTime(string);

Answer 2

Your question is not clear:

Do you want to just format "something representing a date" into a string with time of "00:00:00"?

Or are you trying to convert "something representing a date" into "something representing a date+time, with 00:00:00 as time"?

Or are you trying to convert a java.util.Date to a Joda org.joda.time.DateTime by ignoring the original time and set time to 00:00:00?

Or are you trying to convert a string of date with format of "YYYY-MM-dd" to another String with date+time, with 00:00:00 as time?

Or something else?

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In Joda, the proper way to represent a date is by LocalDate, and the proper way to represent a "date + time" information (but not a instant of time) is by LocalDateTime. DateTime is representing a instant of time. With these basic understanding:

Answer for Q1:

String result = DateTimeFormat.forPattern("YYYY-MM-dd", myLocalDate);

Answer for Q2:

LocalDateTime result = myLocalDate.toLocalDateTime(LocalTime.MIDNIGHT);

Answer for Q3:

DateTime result = new DateTime(javaUtilDate).withTimeAtStartOfDay();

Answer for Q4:

String result = dateString + " 00:00:00";