How to convert ConstraintViolationException 500 error to 400 bad request?

Question

If I use a constraint like this @NotNull and then in the controller

public User createUser(
            @Validated
            @RequestBody User user) {}

It gives a really nice 400 exception with details.

But if I use my own custom validator like this:

public User createUser(
            @UserConstraint
            @RequestBody User user) {}

It throws a 500 server error like this:

javax.validation.ConstraintViolationException: createUser.user: Error with field: 'test35'
    at org.springframework.validation.beanvalidation.MethodValidationInterceptor.invoke(MethodValidationInterceptor.java:117) ~[spring-context-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.security.access.intercept.aopalliance.MethodSecurityInterceptor.invoke(MethodSecurityInterceptor.java:69) ~[spring-security-core-5.1.6.RELEASE.jar:5.1.6.RELEASE]

Is there a way to get nice 400 message to the response?

Ideally the 400 message should be the same as Spring's validation JSON

{
    "timestamp": "2019-10-30T02:33:15.489+0000",
    "status": 400,
    "error": "Bad Request",
    "errors": [
        {
            "codes": [
                "Size.user.lastName",
                "Size.lastName",
                "Size.java.lang.String",
                "Size"
            ],
            "arguments": [
                {
                    "codes": [
                        "user.lastName",
                        "lastName"
                    ],
                    "arguments": null,
                    "defaultMessage": "lastName",
                    "code": "lastName"
                },
                25,
                1
            ],
            "defaultMessage": "size must be between 1 and 25",
            "objectName": "user",
            "field": "lastName",
            "rejectedValue": "",
            "bindingFailure": false,
            "code": "Size"
        }
    ],
    "message": "Validation failed for object='user'. Error count: 1",
    "path": "/api/v1/users"
}

Answer 1

Yes, you can create a custom error handler so you can add anything on your response and status as well. This is the simple way to change the status:

1.- Simple way to change status when ConstraintViolationException is thrown.

import javax.validation.ConstraintViolationException;

@ControllerAdvice
public class CustomErrorHandler {

    @ExceptionHandler(ConstraintViolationException.class)
    public void handleConstraintViolationException(ConstraintViolationException exception,
            ServletWebRequest webRequest) throws IOException {
        webRequest.getResponse().sendError(HttpStatus.BAD_REQUEST.value(), exception.getMessage());
    }
}    

2.- Custom way to put the response when a ConstraintViolationException occurs.

@ControllerAdvice
public class CustomErrorHandler {

    @ExceptionHandler(ConstraintViolationException.class)
    public ResponseEntity<CustomError> handleConstraintViolationException(ConstraintViolationException exception) {
        CustomError customError = new CustomError();
        customError.setStatus(HttpStatus.BAD_REQUEST);
        customError.setMessage(exception.getMessage());
        customError.addConstraintErrors(exception.getConstraintViolations());
        return ResponseEntity.badRequest().body(customError);
    }
}