Bean validation after setter? - bean-validation

Question

I want to validate the trimmed string length, like:
#Size(min = 5, max = 20, message = "Please enter a valid username (5-20 characters)")
String userName;
Given user name foo (6 chars), it will be trimmed to foo (3 chars) in the setter method, however, validate against the raw input seems a bit of useless.

Answer 1

Instead of altering the validation procedure, you could write your own constraint which wraps the expected validation logic.
I have found such an implementation of a #TrimmedSize annotation at the auto-trader-spring-spike project:
package com.autotrader.frameworks;
import javax.validation.Constraint;
import javax.validation.Payload;
import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import static java.lang.annotation.ElementType.*;
#Documented
#Constraint(validatedBy = TrimmedSizeValidator.class)
#Target({METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER})
#Retention(RetentionPolicy.RUNTIME)
public #interface TrimmedSize {
String message() default "size too small";
Class<?>[] groups() default {};
int min() default 0;
Class<? extends Payload>[] payload() default {};
}
And the validator:
package com.autotrader.frameworks;
import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;
public class TrimmedSizeValidator implements ConstraintValidator<TrimmedSize, String> {
private int length;
public void initialize(TrimmedSize trimmedSize) {
length = trimmedSize.min();
}
public boolean isValid(String value, ConstraintValidatorContext constraintValidatorContext) {
if (value == null || value.length() == 0) {
return false;
}
return value.trim().length() >= length;
}
}
It uses an Apache License 2.0, but even then you could write this code from scratch once you've seen it.