JSR-303 Bean Validation - 一个验证器的自定义约束多个注释

Question

在编写自定义约束时，可以通过一个验证器实现来验证多个注释。例如，我有几个注释，它们规定了不同的 @size 注释，但我希望它们都指向同一个验证器类，该验证器类进行一些全局检查，即所有都必须匹配某个正则表达式。据我所知，该实现采用一种注释类型。

一个注释

@Target( { METHOD, FIELD, ANNOTATION_TYPE, TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = {UCNValidator.class})
@Documented
@Size(min = 9, max = 9, message = "{exactlength}")
public @interface UCN {

    String message() default "{invalidFormat}";

    Class<?>[] groups() default {};

    Class<? extends Payload>[] payload() default {};

    String fieldName() default "ucn";

}

验证器

public class UCNValidator implements ConstraintValidator<UCN, String>
{

    private String pattern = "[a-zA-Z].*";
    private String fieldName;

    @Override
    public void initialize( UCN constraintAnnotation )
    {
        this.fieldName = constraintAnnotation.fieldName();
    }

    @Override
    public boolean isValid( String value, ConstraintValidatorContext constraintValidatorContext )
    {

        if ( value != null )
        {
            if ( !value.matches(pattern) )
            {
                //do some stuff
                return false;
            }

        }

        return true;

    }

Answer 1

在验证对象的一个​​属性时，似乎没有办法从对象访问其他值。我使用的解决方案是将注释放在类上，然后验证器将获取整个对象以进行验证，您可以仅访问执行验证所需的信息。

这是我写的一个比较对象的两个不同属性的文章：

@Target(TYPE)
@Retention(RUNTIME)
@Constraint(validatedBy = LessThanValidator.class)
@Documented
public @interface LessThan {

    String message() default "{com.bullethq.constraints.LessThan}";

    String bigValueProperty();

    String littleValueProperty();

    Class<?>[] groups() default {};

    Class<? extends Payload>[] payload() default {};
}

那么验证器类是：

public class LessThanValidator implements ConstraintValidator<LessThan, Object> {

    private LessThan constraint;

    public void initialize(LessThan constraintAnnotation) {
        constraint = constraintAnnotation;
    }

    public boolean isValid(Object object, ConstraintValidatorContext cvc) {
        Object bigValue = getValue(object, constraint.bigValueProperty());
        Object littleValue = getValue(object, constraint.littleValueProperty());

        // If one of the values is null, then we do not perform validation.
        if (bigValue == null || littleValue == null) {
            return true;
        }

        if (bigValue instanceof Comparable && littleValue instanceof Comparable) {
            boolean valid = ((Comparable<Object>) bigValue).compareTo(littleValue) > 0;
            if (!valid) {
                // If the values are not valid, then build a custom violations which has the correct path in it.
                cvc.buildConstraintViolationWithTemplate(cvc.getDefaultConstraintMessageTemplate())
                        .addNode(constraint.littleValueProperty())
                        .addConstraintViolation().disableDefaultConstraintViolation();
            }
            return valid;
        }
        throw new IllegalArgumentException("Properties " + constraint.bigValueProperty() + " and " + constraint.littleValueProperty() + " both need to be comparable in " + object.getClass());
    }
}

getValue() 方法只是一个使用反射从对象中获取值的静态方法。