How to Apply Multiple Date Formats to DateTimeFormatter in Java

We can apply multiple date formats to a DateTimeFormatter using optional sections.

Suppose we’re working with the following date formatter.

DateTimeFormatter formatter1 = DateTimeFormatter
  .ofPattern("yyyy-MM-dd HH:mm:ss");

We want to include a formatter that can parse a different date format, which might look something like this:

DateTimeFormatter formatter2 = DateTimeFormatter
  .ofPattern("ddMMMyyyy:HH:mm:ss.SSS");

1. Entirely different date formats

We can use the optional sections pattern to create multiple optional sections, each delimited by square brackets [].

DateTimeFormatter formatter = DateTimeFormatter
  .ofPattern("[yyyy-MM-dd HH:mm:ss][ddMMMyyyy:HH:mm:ss.SSS]");

This method allows for entire sections of the parsed string (i.e. that enclosed in the brackets []) to be missing.

LocalDateTime.parse("2022-07-14 03:00:00", formatter)
LocalDateTime.parse("14Jul2022:03:00:00.123", formatter)

2. Mildly different date formats

If only a subsection of the format string will be different, we can use the optional section for a substring of the date format.

DateTimeFormatter formatter = DateTimeFormatter
  .ofPattern("yyyy-MM-dd HH:mm:ss[.SSSSSSSSS][.SSS]");

The above DateTimeFormatter will match second, millisecond, and nanosecond timestamps.

LocalDateTime.parse("2022-07-14 03:00:00", formatter)
LocalDateTime.parse("2022-07-14 03:00:00.123", formatter)
LocalDateTime.parse("2022-07-14 03:00:00.123456789", formatter)