Too many connections to postgresql heroku with spring

Question

I have hobby-dev plan PostgreSQL database on Heroku and my Spring application that don't use this database. When I deploy my code Heroku say me, that I use 10 database connections of 20. Can you explain why? None of configuration changes from heroku example help me. My test-server do absolutely nothing but hold this connections... Should i write custom Spring config and if I should, how can I do it?

This is my Controller class code, by the way, application.properties is empty.

@Controller
public class MainController {

    @RequestMapping("/")
    public RedirectView redirect() {
        RedirectView redirectView = new RedirectView();
        redirectView.setUrl("https://google.com/");
        return redirectView;
    }
}