public String getItemValue(final String key) {
        OpenItemDTO openItemDTO = this.apolloOpenApiClient.getItem(
                apolloConfig.getAppId(),
                apolloConfig.getEnv(),
                apolloConfig.getClusterName(),
                apolloConfig.getNamespace(),
                key);
        if (Objects.isNull(openItemDTO)) {
            return null;
        }
        if (openItemDTO.getKey().equals("timeout")) {
            LOG.error("apollo client getItemValue time out");
            throw new ShenyuException("apollo client getItemValue time out");
        }
        return openItemDTO.getValue();
    }
get item value.
@param key item key
@return item value
shenyu-admin-listener/shenyu-admin-listener-apollo/src/main/java/org/apache/shenyu/admin/listener/apollo/ApolloClient.java