Using Joda Date & Time API to parse multiple formats

I'm parsing third party log files containing date/time using Joda. The date/time is in one of two different formats, depending on the age of the log files I'm parsing.

Currently I have code like this:

try {
    return DateTimeFormat.forPattern("yyyy/MM/dd HH:mm:ss").parseDateTime(datePart);
} catch (IllegalArgumentException e) {
    return DateTimeFormat.forPattern("E, MMM dd, yyyy HH:mm").parseDateTime(datePart);
}

This works but contravenes Joshua Bloch's advice from Effective Java 2nd Edition (Item 57: Use exceptions only for exceptional conditions). It also makes it hard to determine if an IllegalArgumentException occurs due to a screwed up date/time in a log file.

Can you suggest a nicer approach that doesn't misuse exceptions?

You can create multiple parsers and add them to the builder by using DateTimeFormatterBuilder.append method:

DateTimeParser[] parsers = { 
        DateTimeFormat.forPattern( "yyyy-MM-dd HH" ).getParser(),
        DateTimeFormat.forPattern( "yyyy-MM-dd" ).getParser() };
DateTimeFormatter formatter = new DateTimeFormatterBuilder().append( null, parsers ).toFormatter();

DateTime date1 = formatter.parseDateTime( "2010-01-01" );
DateTime date2 = formatter.parseDateTime( "2010-01-01 01" );

Joda-Time supports this by allowing multiple parsers to be specified - DateTimeFormatterBuilder#append

Simply create your two formatters using a builder and call toParser() on each. Then use the builder to combine them using append.