Bean validation - validate optional fields - spring

Question

Given a class that represents payload submitted from a form, I want to apply bean validation to a field that may or may not be present, for example:
class FormData {
#Pattern(...)
#Size(...)
#Whatever(...)
private String optionalField;
...
}
If optionalField is not sent in the payload, I don't want to apply any of the validators above, but if it is sent, I want to apply all of them. How can it be done?
Thanks.

Answer 1

So usually all of these constraints consider null value as valid. If your optional filed is null when it's not part of the payload all should work just fine as it is.
And for any mandatory fields you can put #NotNull on them.
EDIT
here's an example:
class FormData {
#Pattern(regexp = "\\d+")
#Size(min = 3, max = 3)
private final String optionalField;
#Pattern(regexp = "[a-z]+")
#Size(min = 3, max = 3)
#NotNull
private final String mandatoryField;
}
#Test
public void test() {
Validator validator = getValidator();
// optonal field is null so no violations will rise on it
FormData data = new FormData( null, "abc" );
Set<ConstraintViolation<FormData>> violations = validator.validate( data );
assertThat( violations ).isEmpty();
// optional field is present but it should fail the pattern validation:
data = new FormData( "aaa", "abc" );
violations = validator.validate( data );
assertThat( violations ).containsOnlyViolations(
violationOf( Pattern.class ).withProperty( "optionalField" )
);
}
You can see that in the first case you don't get any violations as the optional field is null. but in the second exmaple you receive a violation of pattern constraint as aaa is not a string of digits.