When learning Spring Boot, one of the most confusing things is seeing controllers written in many different ways.

Sometimes a method returns a DTO.

Sometimes ResponseEntity<T> .

Sometimes void , String , ModelAndView , CompletableFuture , Mono , and more.

At first it feels random.

But each return type has a specific purpose.

This article is a practical cheat sheet to quickly understand the most common controller patterns in Spring Boot REST APIs.

What Is a Controller?

A controller handles HTTP requests.

Its job is simple:

Receive the request

Call the service layer

Return a response

Example:

@RestController @RequestMapping ( "/api/users" ) public class UserController {

}

Enter fullscreen mode

Exit fullscreen mode

Most Common HTTP Annotations

Annotation HTTP Method Purpose

@GetMapping GET Retrieve data

@PostMapping POST Create data

@PutMapping PUT Replace/update completely

@PatchMapping PATCH Partial update

@DeleteMapping DELETE Delete data

1.…