If using simply the default RestTemplate (by using just new RestTemplate()) and pass it with an url with https, does that mean the connection is using TLS ?
TestRequest request = getTestRequest();
RestTemplate r = new RestTemplate();
String url = "https://FQDN/path/resource";
ResponseEntity<String> resp = r.postForEntity(url, request, String.class);
System.out.println("resp - " + resp.getBody());
I have tried with something like below and the call is successful. Actually, if I change the url to http, the call doesn't work. However, I got confused after getting to learn from somewhere that to use https, it would have to use something like secured RestTemplate (and set some TLS config setting). But from my testing, it seem like by using the default RestTemplate (and pass it with an https url), it would already work.
Yes, RestTemplate can connect to HTTPS endpoints out of the box. If you need mTLS where the client also authenticates itself, you need to configure it.