private Map<String, JavaType[]> getRequestCache() {
        return requestClassCache.computeIfAbsent(getCurrentClassLoader(), k -> new ConcurrentHashMap<>());
    }
Fetch request class for cache according  service and method

@param service    interface name
@param methodName method name
@return request class
codec/codec-jackson/src/main/java/com/alipay/sofa/rpc/codec/jackson/JacksonHelper.java