JSR-303 validation in Spring controller and getting @JsonProperty name

Question

I do validation with JSR-303 in my Spring app, it works as needed.

This is an example:

@Column(nullable = false, name = "name")
    @JsonProperty("customer_name")
    @NotEmpty
    @Size(min = 3, max = 32)
    private String name;

And REST API clients use customer_name as name of input field that send to API bud validation field error org.springframework.validation.FieldError returns name as name of the field.

Is there some way hot to get JSON-ish name that is specified in @JsonProperty? Or do I have to implement own mapper to map class fields name into its JSON alternative?

Edit1: Renaming class fields into names that correspond to JSON names is not alternative (for many reasons).

Rheinland

This answer may give you some insights on how to parse a constraint violation and then use Jackson to find the actual JSON property name. – Whitman

Answer 1

This can now be done by using PropertyNodeNameProvider.

Clypeate

From my initial experimentation, this works for customizing the bean validation ConstraintValidation property names, but fails when Spring converts it to a FieldError, since it expects the actual field name and not the JSON property name. – Transparent

@M.Justin that is true. I opened an issue: github.com/spring-projects/spring-framework/issues/24811 for that, but no response yet. The workaround is to extend org.springframework.validation.beanvalidation.LocalValidatorFactoryBean, and override getRejectedValue to return empty string. This works only if you later (in some @ControllerAdvice) create your own error representation, and not depend on the Spring provided one. – Clypeate

For FieldErrors the only solution I found was to access the private ConstraintViolation from Spring ViolationFieldError via reflection. See the Answer I added. – Comedian

Answer 2

For MethodArgumentNotValidException and BindException I have written a method that tries to access the private ConstraintViolation from Spring ViolationFieldError via reflection.

  /**
   * Try to get the @JsonProperty annotation value from the field. If not present then the
   * fieldError.getField() is returned.
   * @param fieldError {@link FieldError}
   * @return fieldName
   */
  private String getJsonFieldName(final FieldError fieldError) {
    try {
      final Field violation = fieldError.getClass().getDeclaredField("violation");
      violation.setAccessible(true);
      var constraintViolation = (ConstraintViolation) violation.get(fieldError);
      final Field declaredField = constraintViolation.getRootBeanClass()
          .getDeclaredField(fieldError.getField());
      final JsonProperty annotation = declaredField.getAnnotation(JsonProperty.class);
      //Check if JsonProperty annotation is present and if value is set
      if (annotation != null && annotation.value() != null && !annotation.value().isEmpty()) {
        return annotation.value();
      } else {
        return fieldError.getField();
      }
    } catch (Exception e) {
      return fieldError.getField();
    }
  }

This code can be used in methods handling BindExceptions @ExceptionHandler(BindException.class) within a Class with @ControllerAdvice:

@ControllerAdvice
public class ControllerExceptionHandler {

  @ExceptionHandler(BindException.class)
  public ResponseEntity<YourErrorResultModel> handleBindException(final BindException exception) {
    for (FieldError fieldError : exception.getBindingResult().getFieldErrors()) {
      final String fieldName = getJsonFieldName(fieldError);
   ...
}

Comedian

You don't have to use introspection to get at the violation: just use if (fieldError.contains(ConstraintViolation.class) { var violation = fieldError.unwrap(ConstraintViolation.class); ...} – Theone

Answer 3

Here is the function that gets value from @JsonProperty annotation.

private String getJsonPropertyValue(final FieldError error) {
    try {
        if (error.contains(ConstraintViolation.class)) {
            final ConstraintViolation<?> violation = error.unwrap(ConstraintViolation.class);
            final Field declaredField = violation.getRootBeanClass().getDeclaredField(error.getField());
            final JsonProperty annotation = declaredField.getAnnotation(JsonProperty.class);

            if (annotation != null && annotation.value() != null && !annotation.value().isEmpty()) {
                return annotation.value();
            }
        }
    } catch (Exception ignored) {
    }

    return error.getField();
}

Then in your exception handler

@ExceptionHandler(MethodArgumentNotValidException.class)
@ResponseStatus(HttpStatus.BAD_REQUEST)
public ResponseEntity<?> validationExceptionHandler(MethodArgumentNotValidException e) {
    final Map<String, String> errors = new HashMap<>();
    e.getBindingResult().getAllErrors().forEach((error) -> {
        String fieldName = getJsonPropertyValue((FieldError) error);
        String errorMessage = error.getDefaultMessage();
        errors.put(fieldName, errorMessage);
    });
    System.out.println(errors); // put this in your response
    return ResponseEntity.badRequest().build();
}

Amphigory

Answer 4

There is no way to achieve this currently. We have an issue for this in the reference implementation: HV-823.

This would address the issue on the side of Hibernate Validator (i.e. return the name you expect from Path.Node#getName()), it'd require some more checking whether Spring actually picks up the name from there.

Maybe you'd be interested in helping out with implemeting this one?

Tungus

A while ago I wrote this answer. It's about how to parse a constraint violation and then use Jackson to find the actual JSON property name. – Whitman

Spring got the "field" name from SpringValidatorAdapter.determineField(ConstraintViolation<Object> violation), and as per Javadoc: The default implementation returns the stringified property path. By default in Spring application, the actual instance of SpringValidatorAdapter is of subclass LocalValidatorFactoryBean. – Labarum