private void addFallback(final String key, final FallbackHolder holder) {
        FallbackHolder oldObj = fallsRegisters.get(key);
        if (Objects.nonNull(oldObj)) {
            return;
        }
        FallbackRegisterTask registryTask = new FallbackRegisterTask(key, this);
        fallsRegisters.put(key, holder);
        timer.add(registryTask);
        LOG.info("Add to Fallback and wait for execution, {}:{}:{}", holder.getNamespaceId(), holder.getSelectorName(), holder.getUriList());
    }
Register uri string.

@param selectorName the selector name
@param uriList      the uri list
@return the string
shenyu-admin/src/main/java/org/apache/shenyu/admin/service/register/FallbackShenyuClientRegisterService.java