private String getSubNodeKeyName(final String prefix, final String fullPath, final String separator) {
        if (prefix.length() > fullPath.length()) {
            return null;
        }
        String pathWithoutPrefix = fullPath.substring(prefix.length());
        return pathWithoutPrefix.contains(separator) ? pathWithoutPrefix.substring(1) : pathWithoutPrefix;
    }
get keyPrefix map.

@param prefix    key prefix.
@param separator separator char
@param map prefix map
@return sub map
shenyu-sync-data-center/shenyu-sync-data-etcd/src/main/java/org/apache/shenyu/sync/data/etcd/EtcdClient.java