Springboot show error message for invalid date (YearMonth) formats: eg 2020-15 - spring-boot

Question

I have a project with Spring Boot and I want to show an error response if the given date format is incorrect.
The correct format is yyyy-MM (java.time.YearMonth) but I want to want to show a message if someone sends 2020-13, 2020-111 or 2020-1.
When I've added a custom validator the debugger goes in there with a valid request but not with an incorrect request. I also tried to use the message.properties with the typeMismatch.project.startdate=Please enter a valid date. but I also don't see that message in my response body.
It seems like the application does not understand my incorrect request and then always throws a BAD REQUEST with empty body, which is not strange because it is not a valid date.
Can someone explain me how I can show an errormessage in the response for these incorrect values?
Or is there no other way then use a String and convert that to the YearMonth object so I can show catch and show an error message?
Request object:
#Getter
#Setter
public class Project {
#NotNull(message = "mandatory")
#DateTimeFormat(pattern = "yyyy-MM")
private YearMonth startdate;
}
Controller:
#RestController
#RequestMapping(produces = MediaType.APPLICATION_JSON_VALUE)
public class ProjectController {
#PostMapping(value = "/project", consumes = MediaType.APPLICATION_JSON_VALUE)
public Project newProject(#Valid #RequestBody Project newProject) {
return projectService.newProject(newProject);
}
}
ExceptionHandler:
#RestControllerAdvice
public class GlobalExceptionHandler extends ResponseEntityExceptionHandler {
#SneakyThrows
#Override
protected ResponseEntity<Object> handleMethodArgumentNotValid(MethodArgumentNotValidException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
headers.add("Content-Type", "application/json");
ObjectMapper mapper = new ObjectMapper();
Map<String, String> errors = new HashMap<>();
ex.getBindingResult().getAllErrors().forEach(error -> {
String name;
if (error instanceof FieldError)
name = ((FieldError) error).getField();
else
name = error.getObjectName();
String errorMessage = error.getDefaultMessage();
errors.put(name, errorMessage);
});
return new ResponseEntity<>(mapper.writeValueAsString(errors), headers, status);
}
}

Answer 1

Okay, I made a solution which is workable for me.
I've added the solution below for people who find this thread in the future and has the same problem I had.
Create a custom validator with a simple regex pattern:
#Target({ FIELD })
#Retention(RUNTIME)
#Constraint(validatedBy = YearMonthValidator.class)
#Documented
public #interface YearMonthPattern {
String message() default "{YearMonth.invalid}";
Class<?>[] groups() default { };
Class<? extends Payload>[] payload() default { };
}
public class YearMonthValidator implements ConstraintValidator<YearMonthPattern, String> {
#Override
public boolean isValid(String value, ConstraintValidatorContext context) {
Pattern pattern = Pattern.compile("^([0-9]{4})-([0-9]{2})$");
Matcher matcher = pattern.matcher(value);
try {
return matcher.matches();
} catch (Exception e) {
return false;
}
}
}
Update the request object:
#Getter
#Setter
public class Project {
#NotNull(message = "mandatory")
#YearMonthPattern
private String startdate;
public YearMonth toYearMonth(){
return YearMonth.parse(startdate);
}
}
The DateTimeFormat annotation is replaced with our new custom validator and instead of a YearMonth, make it a String. Now the validator annotation can be executed because the mapping to the YearMonth won't fail anymore.
We also add a new method to convert the String startdate to a YearMonth after Spring has validated the request body, so we can use it in the service as a YearMonth instead of having to translate it each time.
Now when we send a requestbody with:
{
"startdate": "2020-1"
}
we get a nice 400 bad request with the following response:
{
"endDate": "{YearMonth.invalid}"
}