Tienes que empezar a probar cosas.
Examinar la excepción (las de SQL pueden llegar encapsuladas), hacer un ping desde código a la BBDD, usar otra query que no tenga que ver, probar esa misma query directamente en mysql, si usas una PreparedStatement probar con Statement...
http://stackoverflow.com/questions/2...tions-link-fai Cita: If you get a SQLException: Connection refused or Connection timed out or a MySQL specific CommunicationsException: Communications link failure, then it means that the DB isn't reachable at all. This can have one or more of the following causes:
IP address or hostname in JDBC URL is wrong.
Hostname in JDBC URL is not recognized by local DNS server.
Port number is missing or wrong in JDBC URL.
DB server is down.
DB server doesn't accept TCP/IP connections.
DB server has run out of connections.
Something in between Java and DB is blocking connections, e.g. a firewall or proxy.