Parsing dates in multiple formats in Joda-Time
Joda-Time is without a doubt the best way to work with dates and times in Java, unless you happen to be working exclusively on Java 8+, where you can use the new java.time library, also known as JSR 310.
With Joda you can easily parse dates, times and timestamps using DateTimeFormatter. For example you can use:
DateTimeFormatter formatter = DateTimeFormat.forPattern("yyyy-MM-dd");
LocalDate date = formatter.parseLocalDate("2015-12-25");
assertEquals(2015, date.getYear());
assertEquals(12, date.getMonthOfYear());
assertEquals(25, date.getDayOfMonth());
However, the library doesn’t have a method such as “tryParse”: it only has various versions of parseLocalDate, parseLocalTime, parseDateTime which all throw IllegalArgumentException if the given string doesn’t match the format.
So, what if you need to parse a date in one of two possible formats? You can obviously do something like this:
private static final List<DateTimeFormatter> FORMATTERS =
Arrays.asList(
DateTimeFormat.forPattern("dd/MM/yyyy"),
DateTimeFormat.forPattern("yyyy-MM-dd"));
public static LocalDate parseDate(String inputString)
throws IllegalArgumentException {
for (DateTimeFormatter formatter : FORMATTERS) {
try {
return formatter.parseLocalDate(inputString);
} catch (IllegalArgumentException e) {
// Go on to the next format
}
}
throw new IllegalArgumentException("Unsupported date format: " + inputString);
}
@Test
public void testMatchedFormatsReturnTheDate() {
assertEquals(new LocalDate(2015, 12, 25), parseDate("25/12/2015"));
assertEquals(new LocalDate(2015, 12, 25), parseDate("2015-12-25"));
}
@Test(expected = IllegalArgumentException.class)
public void testUnmatchedFormatThrows() {
parseDate("25.12.2015");
}
However, this is not very nice, not to mention not very fast since throwing an exception in Java can be quite expensive.
A better alternative exists though: you can use DateTimeFormatterBuilder to create a DateTimeFormatter with multiple patterns. For example:
private static final DateTimeFormatter DATE_FORMATTER =
new DateTimeFormatterBuilder()
.append(null, new DateTimeParser[]{
DateTimeFormat.forPattern("dd/MM/yyyy").getParser(),
DateTimeFormat.forPattern("yyyy-MM-dd").getParser()})
.toFormatter();
@Test
public void testMatchedFormatsReturnTheDate() {
assertEquals(new LocalDate(2015, 12, 25), DATE_FORMATTER.parseLocalDate("25/12/2015"));
assertEquals(new LocalDate(2015, 12, 25), DATE_FORMATTER.parseLocalDate("2015-12-25"));
}
@Test(expected = IllegalArgumentException.class)
public void testUnmatchedFormatThrows() {
DATE_FORMATTER.parseLocalDate("25.12.2015");
}
This is a simpler alternative to the previous version, not only because it’s more readable (using exception as control flow is not a good design), but also because the returned object simply implements the same interface as a parser for just one format, allowing you to simply not care whether it supports one or more formats. Win-win!