@Controller vs @RestController in Spring MVC

Direct Answer

@Controller marks a Spring MVC controller; its methods can render views or write response bodies. @RestController combines @Controller with class-level @ResponseBody, so its handler return values are written through HttpMessageConverters by default. JSON is common but not required. A @Controller method can also return data by adding @ResponseBody or ResponseEntity.

Code Example

// @Controller — returns a VIEW NAME, resolved to HTML by ViewResolver
@Controller
class PageController {
    @GetMapping("/home")
    public String home(Model model) {
        model.addAttribute("user", "Alice");
        return "home"; // -> templates/home.html (Thymeleaf)
    }
}

// @RestController = @Controller + @ResponseBody — returns DATA as JSON
@RestController
@RequestMapping("/api")
class UserApi {
    @GetMapping("/users/{id}")
    public User getUser(@PathVariable Long id) {
        return new User(id, "Alice"); // -> {"id":1,"name":"Alice"}
    }
}

record User(Long id, String name) {}

The same DispatcherServlet routes both — only the implicit @ResponseBody behavior differs.

Common Mistakes & Pitfalls

• Forgetting @ResponseBody: Using @Controller for REST endpoints and not adding @ResponseBody to methods. Spring tries to resolve the returned object as a view name, resulting in "template not found" errors. You see 404s or "Could not resolve view" exceptions.
• Mixing Annotations: Using @RestController but trying to return view names — doesn't work because @ResponseBody is applied to all methods.
• Not Understanding Jackson: Freshers don't realize @RestController triggers automatic JSON serialization. They manually build JSON strings or use ObjectMapper explicitly when Jackson does it automatically for POJOs.