SimpleDateFormat with only milliseconds

Question

I must use a SimpleDateFormat to parse a date in Java. I'm using an existing library that takes a date as String and a SimpleDateFormat instance to parse it. Everything is fine, but I'm having trouble if the date format consists in only milliseconds since epoch time (1/1/1970), i.e. UNIX time in milliseconds. Using new SimpleDateFormat("SS") or new SimpleDateFormat("SSS") didn't work:

Code to reproduce the strange SimpleDateFormat behavior:

TimeZone.setDefault(TimeZone.getTimeZone("GMT")); // just for the test
long currTimeInMilli = System.currentTimeMillis();

SimpleDateFormat msSDF = new SimpleDateFormat("SS");  // same result with SimpleDateFormat("SSS")
SimpleDateFormat secSDF = new SimpleDateFormat("ss");

System.out.println(msSDF.parse("" + currTimeInMilli));
System.out.println(secSDF.parse("" + (currTimeInMilli / 1000)));
System.out.println(new SimpleDateFormat("EEE MMM dd HH:mm:ss zz yyyy").format(currTimeInMilli));

Produced output:

Mon Dec 15 07:46:20 GMT 1969    <-- should be like two other lines (?)!
Mon Apr 28 20:55:19 GMT 2014    <-- OK
Mon Apr 28 20:55:19 GMT 2014    <-- OK

Is it normal? How can I set up a SimpleDateFormat able to parse milliseconds elapsed since the epoch?

Notes:

• I cannot use other libraries like Joda-time
• I cannot use new Date(long pNbMilli) to construct the date (legacy library is taking a SimpleDateFormat instance as input)
• I found this filed JDK bug but not sure it is directly bound to this issue...

Answer 1

The S pattern won't properly handle a number of milliseconds greater than Integer.MAX_VALUE, as bizarre as that may seem for a quantity normally expressed as a long.

If you really must use an existing API that demands a DateFormat you can always hack it in:

SimpleDateFormat msSDF = new SimpleDateFormat("SSS") {

            @Override
            public Date parse(String source) throws ParseException {
                return new Date(Long.parseLong(source));
            }

}; 

(May need to also provide a hacked implementation of format(string) too depending on what your legacy API actually does of course.)