Why Spring @Autowired field is null and how to fix it?

Hello everyone. I'm new to Spring and encountered an unclear problem. I have a `UserService` service that I want to inject into a controller using the `@Autowired` annotation. But when trying to call a service method, I get a `NullPointerException` — the `userService` field is `null`. Here is my code: ```java public class UserController { @Autowired private UserService userService; public void handleRequest() { userService.getUser(1); // NullPointerException here } } @Service public class UserService { public String getUser(int id) { return "User " + id; } } ``` I also tried using `@Component` on the controller, but that didn't help. I didn't configure anything in `applicationContext.xml` — I thought Spring Boot would handle everything automatically. The project