Extending @NotEmpty to accept other classes

Question

I've been trying to make a custom validator so i can just use the @NotEmpty annotation for specific classes (java.util.Calendar or CommandItem in this case). But i get an exception:

javax.validation.UnexpectedTypeException: No validator could be found for type: com.bla.DocumentCommandItem 

Now, the only thing i can think of as to why it doesn't work is that the @NotEmpty annotation itself declares this:

@Constraint(validatedBy = { })

So there is no direct association to the Validator class. But then how does it validate Strings and Collections?

This is my Validator class:

    public class DocumentNotEmptyExtender implements ConstraintValidator<NotEmpty,DocumentCommandItem> {

@Override
public void initialize( NotEmpty annotation ) {
}

@Override
public boolean isValid( DocumentCommandItem cmdItem, ConstraintValidatorContext context ) {
    if ( !StringUtils.hasText( cmdItem.getId() ) && (cmdItem.getFilename() == null || cmdItem.getFilename().isEmpty()) ) {
        return false;
    } else {
        return true;
    }
}

}

Is this even possible?

(as a side note... I've also received this exception when i was making my own similar annotation, but that one mysteriously disappeared. )

Thanks!

Answer 1

You have to register your validator in a constraint mapping file like this:

<constraint-mappings
    xmlns="http://jboss.org/xml/ns/javax/validation/mapping"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation=
        "http://jboss.org/xml/ns/javax/validation/mapping validation-mapping-1.0.xsd">

    <constraint-definition annotation="org.hibernate.validator.constraints.NotEmpty">
        <validated-by include-existing-validators="true">
            <value>com.foo.NotEmptyValidatorForDocumentCommandItem</value>
        </validated-by>
    </constraint-definition>
</constraint-mappings>

This mapping file must be registered in META-INF/validation.xml:

<validation-config xmlns="http://jboss.org/xml/ns/javax/validation/configuration"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://jboss.org/xml/ns/javax/validation/configuration">

    <constraint-mapping>/your-mapping.xml</constraint-mapping>
</validation-config>

You can learn more in the Hibernate Validator reference guide and the Bean Validation specification.

Answer 2

The solution is listed above by @Gunnar

It caused a few unexepected things though...

NotEmpty is basically a wrapper for the @NotNull and @Size(min=1) constraints. So there is no actual @NotEmpty implementation.

Making my own @NotEmpty implementation for DocumentCommandItem caused 2 things:

• Validator triggering a NotNull and Size validation (and thus a 'no validator found' for the Size-DocumentCommandItem combo
• More importantly, Size-String validations started to fail because it could not find an implementation for it.

So my final solution for this problem:

Make a @Size implementation for DocumentCommandItem And Make a @NotEmpty implementation for String

(and possibly i'll have to make another @NotEmpty for Collections)