Jackson deserialization errorhandling in spring-framework - spring

Question

I'm looking for a clean way to handle Jackson Deserialization errors for REST web requests.
More precisely: I have an Enum in a incoming DTO object, mapped from JSON. But if the user sends a wrong value, a 400 Bad Request is returned. I would like to return a 422 Unprocessable Entity with a correct message.
One option would be to accept a String, and use bean validation. However, it's not possible to pass all enum values as a list to the annotation (not a constant), so I would need to pass all enum values separately and keep them up to date. This will be very error prone over the whole application. I'm looking for a more structural way to handle this.

Answer 1

I solved this by using a String in the DTO and using a public #interface EnumValueas annotation.
The EnumValue:
#ReportAsSingleViolation
#Documented
#Retention(RetentionPolicy.RUNTIME)
#Constraint(validatedBy = EnumValueValidator.class)
#Target(ElementType.FIELD)
public #interface EnumValue {
Class<? extends Enum> value();
String message() default "The input contains validation errors.";
Class<?>[] groups() default { };
Class<? extends Payload>[] payload() default { };
}
The validator:
public class EnumValueValidator implements ConstraintValidator<EnumValue, String> {
private Class<? extends Enum> enumClass;
private String message;
#Override
public void initialize(final EnumValue constraintAnnotation) {
this.enumClass = constraintAnnotation.value();
this.message = constraintAnnotation.message();
}
#Override
public boolean isValid(final String value, final ConstraintValidatorContext context) {
boolean valid = false;
for (final Enum enumValue : enumClass.getEnumConstants()) {
if (enumValue.name().equals(value)) {
valid = true;
}
}
if (!valid) {
context.buildConstraintViolationWithTemplate(message) //
.addConstraintViolation();
}
return valid;
}
}