When using @RestController, is a new instance of the service created for each HTTP request or is the same object used?

When using the @RestController annotation in Spring Boot services, they are typically singletons by default. This means that for each HTTP request, a new instance of the controller or service is not created; instead, the same object is used.

Spring manages the lifecycle of beans and by default creates them as singletons, which improves performance and conserves resources.

If you need to create a new instance for each request, you can change the scope of the bean, for example, using the @Scope("request") annotation.

Example:

@Service
public class MyService {
    // singleton service by default
}

@RestController
public class MyController {
    private final MyService myService;

    public MyController(MyService myService) {
        this.myService = myService;
    }

    @GetMapping("/hello")
    public String hello() {
        return "Hello";
    }
}

Here, MyService and MyController are singletons, with one instance for the entire application.