[Solved] Given this controller method: @PostMapping("/users") public ResponseEntity createUser(@Valid @RequestBody... } What happens if the client sends a request with an empty required field in UserDto? | Spring Boot

Spring Boot - Request and Response Handling

Given this controller method:

@PostMapping("/users")
public ResponseEntity createUser(@Valid @RequestBody UserDto user) {
    return ResponseEntity.ok("User created");
}

What happens if the client sends a request with an empty required field in UserDto?

ASpring Boot returns a 400 Bad Request with validation error details.

BThe request is ignored silently.

CSpring Boot returns a 500 Internal Server Error.

DThe method executes and returns "User created".

Step-by-Step Solution

Solution:

Step 1: Recognize validation on @Valid @RequestBody
The @Valid annotation triggers validation of the UserDto fields before method execution.
Step 2: Understand behavior on validation failure
If a required field is empty, validation fails and Spring Boot returns a 400 Bad Request with error details.
Final Answer:
Spring Boot returns a 400 Bad Request with validation error details. -> Option A
Quick Check:
Validation failure returns 400 error = D [OK]

Quick Trick: Validation errors return 400 Bad Request automatically [OK]

Common Mistakes:

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