Validate json values in response body before sending to spring controller to avoid response code 400

Question

My Spring controller accepts application json response body as an object parameter. I don't see where I can intercept the json to validate the values before Spring controller receives it and complains when it doesn't cast.

Example: User sends json to endpoint - /createUser

Expecting: {"username":"johndoe", "pin": 1234} Receives: {"username": 1234, "pin": "johndoe"}

If string is sent for int or vice versa, server will show status 400. I'd like to validate the data myself and provide a custom json that details the values that are incorrectly set.

Thanks in advance!

Answer 1

You could create your own class for the @RequestBody param in your controller and make a validation on them. You could use some supported annotations or create on your own. But don't forget to put the @Valid next to the @RequestBody, that's the key. E.g

@RestController
public class UserController {

    @PostMapping("/users")
    ResponseEntity<String> addUser(@Valid @RequestBody User user) {
        // persisting the user
        return ResponseEntity.ok("User is valid");
    }
    
    // standard constructors / other methods
    
}

For more information, you could find them here validation, create your own validator.