datetime - Custom date format cannot be parsed. (Java)

Question

I have to use a custom date format in Java. It contains microseconds although Java doesn't provide support for microseconds. Because of that I filled the time pattern with zeroes, which work fine when formatting, but I cannot parse date-strings with that pattern.

Is there a simple workaround or must I handle microseconds on my own (with String functions)?

@Test
public void testDateFormat() throws ParseException {
    DateFormat format = new SimpleDateFormat("yyyy-MM-dd-HH.mm.ss.SSS000");
    String theDate = format.format(new Date());
    // this will fail:
    format.parse(theDate);
}

java.text.ParseException: Unparseable date: "2010-01-25-12.40.35.769000"

Answer 1

Your problem is that the pattern used in SimpleDateFormat unfortunately have different meanings depending on whether it is used as a parser or as a formatter. As a formatter, your pattern does what is expected, the output will end with the millisecond value formatted as three digits followed by three 0 characters, e.g:

2010-01-25-14.17.47.307000

Used as a parser, the "SSS" pattern will however match an arbitrary number of digits and parse the above example as 307000 ms. After having parsed the ms field, the parser will still look for a "000" substring and fail with an exception, since you've reached the end of the input string, without fulfilling the requirements of the pattern.

Since there is no pattern for a μs value in SimpleDateFormat, you will have to write your own wrapper to strip the input string for the last three 0 characters, before feeding it to SimpleDateFormat.