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Spring Boot REST Controller🌱 Beginner
A controller handles incoming web requests. @RestController marks a class whose methods return data (serialized to JSON) directly — the foundation of a REST API.
A basic controller
HelloController.java
@RestController
public class HelloController {
@GetMapping("/hello")
public String hello() {
return "Hello, Spring Boot!";
}
}Run the app and open http://localhost:8080/hello. @RestController = @Controller + @ResponseBody, so return values become the response body.
Returning JSON automatically
Return an object or list and Spring converts it to JSON with Jackson — no manual serialization.
UserController.java
@GetMapping("/user")
public User getUser() {
return new User(1, "Asha"); // -> {"id":1,"name":"Asha"}
}Controlling the status & headers
Wrap the body in ResponseEntity when you need a specific status code or headers.
UserController.java
@PostMapping("/users")
public ResponseEntity<User> create(@RequestBody User u) {
User saved = service.save(u);
return ResponseEntity.status(HttpStatus.CREATED).body(saved); // 201
}
@GetMapping("/users/{id}")
public ResponseEntity<User> find(@PathVariable Long id) {
return service.find(id)
.map(ResponseEntity::ok) // 200
.orElse(ResponseEntity.notFound().build()); // 404
}Tip: For a real API, keep controllers thin — they receive the request, delegate to a service, and return a response. Put business logic in the service layer, not the controller.
Spring Boot Key Takeaway: Spring Security enforces non-repudiation and access control via security filter chains, protecting against CSRF and unauthenticated endpoints.
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