@Override
    public boolean isReadable(
            Class<?> type,
            Type genericType,
            Annotation[] annotations,
            MediaType mediaType) {
        if (!hasMatchingMediaType(mediaType)) {
            return false;
        }

        if (!isAssignableFrom(type, DEFAULT_UNREADABLES)) {
            return false;
        }

        return isValidType(type, annotations);
    }
Method that JAX-RS container calls to try to check whether values of
given type (and media type) can be deserialized by this provider.
fastjson1-compatible/src/main/java/com/alibaba/fastjson/support/jaxrs/FastJsonProvider.java