public long getSize(Object t, //
                        Class<?> type, //
                        Type genericType, //
                        Annotation[] annotations, //
                        MediaType mediaType) {
        return -1;
    }
Method that JAX-RS container calls to try to figure out serialized length
of given value. always return -1 to denote "not known".
src/main/java/com/alibaba/fastjson/support/jaxrs/FastJsonProvider.java