Java JDBC connection status

Nothing. Just execute your query. If the connection has died, either your JDBC driver will reconnect (if it supports it, and you enabled it in your connection string--most don't support it) or else you'll get an exception.

If you check the connection is up, it might fall over before you actually execute your query, so you gain absolutely nothing by checking.

That said, a lot of connection pools validate a connection by doing something like SELECT 1 before handing connections out. But this is nothing more than just executing a query, so you might just as well execute your business query.

Your best chance is to just perform a simple query against one table, e.g.:

select 1 from SOME_TABLE;

Oh, I just saw there is a new method available since 1.6:

java.sql.Connection.isValid(int timeoutSeconds):

Returns true if the connection has not been closed and is still valid. The driver shall submit a query on the connection or use some other mechanism that positively verifies the connection is still valid when this method is called. The query submitted by the driver to validate the connection shall be executed in the context of the current transaction.