What is a RestController in Spring MVC?

@RestController is a convenience annotation combining @Controller and @ResponseBody, meaning every handler method's return value is written directly to the HTTP response body - typically serialized to JSON by Jackson - instead of being resolved to a view template.

@RestController
@RequestMapping("/api/books")
public class BookController {
    @GetMapping("/{id}")
    public Book getBook(@PathVariable Long id) {
        return bookService.findById(id);
    }
}

Without @RestController (using plain @Controller instead), returning a Book object from a method annotated only with @GetMapping would be treated as a view name to resolve, which usually isn't what you want for a REST API. @RestController is the standard choice for building JSON-based backend services.

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