Anledningen är att drivrutinen inte har laddats i biblioteken, den instansieras inte i anslutningen så anslutningen misslyckades:
try {
String connectionURL = "jdbc:mysql://host/db";
Connection connection = null;
Class.forName("com.mysql.jdbc.Driver").newInstance();
connection = DriverManager.getConnection(connectionURL, "username", "password");
if(!connection.isClosed())
out.println("Successfully connected to " + "MySQL server using TCP/IP...");
connection.close();
}catch(Exception ex){
out.println("Unable to connect to database"+ex);
}