Custom annotation to validate string against enum type

Question

I am trying to write a custom annotation that would validate a String against a specific Enum. I am using Hibernate Validator API. The desired use-case would look like follows.

@MessageTypeOf(MessageType.NETWORK)
private String message;

The String should be validated against the value given from the toString() method of the enum given as the enum argument (in this case, MessageType.NETWORK).

I have written a validator and looks like this.

public class MessageTypeValidator implements ConstraintValidator<MessageTypeOf, String> {

    private Set<String> values;

    @Override
    public void initialize(MessageTypeOf constraintAnnotation) {
        values = Arrays.asList(MessageType.values())
                .stream()
                .map(v -> v.toString())
                .collect(Collectors.toSet());
    }

    @Override
    public boolean isValid(String s, ConstraintValidatorContext constraintValidatorContext) {
        if (s == null) return false;

        return values.contains(s);
    }
}

And the annotation.

@Target({ FIELD, METHOD, PARAMETER, ANNOTATION_TYPE, TYPE_USE })
@Retention(RUNTIME)
@Constraint(validatedBy = MessageTypeValidator.class)
@Documented
public @interface MessageTypeOf {

    String message() default "{org.hibernate.validator.referenceguide.chapter06.CheckCase." +
            "message}";

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

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

    MessageType value();

    @Target({ FIELD, METHOD, PARAMETER, ANNOTATION_TYPE })
    @Retention(RUNTIME)
    @Documented
    @interface List {
        MessageType[] value();
    }
}

However, this would validate if a string is part of the enum (any value), where as I need to validate against a specific one. Could someone suggest how to do that?

Is there a reason you're not just using the enum as the field type directly? — chrylis -cautiouslyoptimistic-
– chrylis -cautiouslyoptimistic-, Commented Dec 18, 2017 at 22:27

JB Nizet · Accepted Answer · 2017-12-18 22:21:41Z

1

So, basically, the only valid value of the property would be MessageType.NETWORK.toString(), is that right? That's quite strange (expecting the client to provide a string that can only have one valid value), but anyway, you just need to check that:

public class MessageTypeValidator implements ConstraintValidator<MessageTypeOf, String> {

    private String validValue;

    @Override
    public void initialize(MessageTypeOf constraintAnnotation) {
        this.validValue = constraintAnnotation.value().toString();
    }

    @Override
    public boolean isValid(String s, ConstraintValidatorContext constraintValidatorContext) {
        return this.validValue.equals(s);
    }
}

answered Dec 18, 2017 at 22:21

JB Nizet

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