Hi and thanks for using our agent 
In order to trace a span (JDBC span in this instance), it needs to made within a traced transaction (see more in our data model documentation).
Since this is done from the Main class, there is no active transaction. If you want to test such code, you can use our public API to create a transaction before and end end it after you make the DB query.
Alternatively, you can test your code from within a Servlet running on a supported servlet container.
I hope this helps,
Eyal.