TimeZone validation in Java

Question

I have a string, I need to check whether it is a standard time zone identifier or not. I am not sure which method I need to use.

String timeZoneToCheck = \"UTC\"         


        

Answer 1

Since TimeZone#getTimeZone(String id) returns a default if the value is invalid (rather than returning an invalid time zone), if the reinterpreted value does not match the initial value, it wasn't valid.

private static boolean isValidTimeZone(@Nonnull String potentialTimeZone)
{
    // If the input matches the re-interpreted value, then the time zone is valid.
    return TimeZone.getTimeZone(potentialTimeZone).getID().equals(potentialTimeZone);
}

Answer 2

You can write it in one line

public boolean validTimeZone(String timezone) {
    return Set.of(TimeZone.getAvailableIDs()).contains(timezone);
}

Alternatively, you can make a static field for it

private static final Set<String> TIMEZONES = Set.of(TimeZone.getAvailableIDs())

public boolean validTimeZone(String timezone) {
    return TIMEZONES.contains(timezone);
}

Answer 3

You can use TimeZone.getAvailableIDs() to get list of supported Id

for (String str : TimeZone.getAvailableIDs()) {
    if (str.equals("UTC")) {
        //found
    }
}