Most databases support a datetime or timestamp datatype directly. If this is an option, avoid using strings as they cannot be ordered easily (unless you choose a workable format).
JDBC supports DATE, TIME, and TIMESTAMP. If your value represents a point in time, don't split it up.
Of course, you'll always be able to find a case where separating them is a better choice. In the end you have to use your best judgment which usually comes from making the wrong choice and learning from your mistake.
