@Size(min, max) but not required

问题

Hi In my spring webapp I have a password variable which I want to be at least 0 characters or more than 6 and less than 20. I know that there is annotation:

 @Size(min=6, max=20)

but I have no idea how to add possibility that password can be 0 characters. Will somebody help me with this?

回答1:

Given the comment, you can use StringTrimmerEditor to convert empty string to null, and then @Size check will not trigger (null is considered as valid in @Size).

In your controller add following method:

@InitBinder
public void initBinder(WebDataBinder binder) {
    binder.registerCustomEditor(String.class, new StringTrimmerEditor(true));
}

Note that StringTrimmerEditor also trims input from spaces, and if you only want one property to be affected by this editor use registerCustomEditor(Class<?> requiredType, String propertyPath, PropertyEditor propertyEditor).

回答2:

If you want a String which is either empty ("") or between 6 and 20 characters long, you could specify a regular expression using the @Pattern constraint:

@Pattern(regexp="(^$|.{6,20})")

回答3:

You can use ConstraintComposition, at least in Hibernate Validator 5.

回答4:

I think you want a nullable field, but that also could be min = 6 and max = 20. AFAIK, @Size should only activate if the field is non-null.

If you're sending an empty string "", it will be validated.

来源：https://stackoverflow.com/questions/11550324/sizemin-max-but-not-required