NullableEnumConverter.java

NullableEnumConverter.java

public class NullableEnumConverter implements ModelConverter {

    @Override
    public Schema<?> resolve(AnnotatedType type, ModelConverterContext context, Iterator<ModelConverter> chain) {

        var schema = chain.next().resolve(type, context, chain);

        if (isNull(schema)) {
            return schema;
        }

        var javaType = Json.mapper().constructType(type.getType());

        if (!javaType.isEnumType()) {
            return schema;
        }

        var annotation = findAnnotation(type, javaType);

        if (nonNull(annotation) && schema instanceof StringSchema) {
            var stringSchema = (StringSchema) schema;
            stringSchema.addEnumItem(null);
        }

        return schema;

    }

    Annotation findAnnotation(AnnotatedType type, JavaType javaType) {
        var annotation = javaType.getRawClass().getAnnotation(NullableEnum.class);

        if (annotation != null) {
            return annotation;
        }

        for (var contextAnnotation : type.getCtxAnnotations()) {
            if (contextAnnotation.annotationType().equals(NullableEnum.class)) {
                return contextAnnotation;
            }
        }

        return null;
    }

    @Retention(RetentionPolicy.RUNTIME)
    public @interface NullableEnum {
    }
}