code: public static String encodedEntry(String bucket, String key) {
          String encodedEntry;
          if (key != null) {
              encodedEntry = UrlSafeBase64.encodeToString(bucket + ":" + key);
          } else {
              encodedEntry = UrlSafeBase64.encodeToString(bucket);
          }
          return encodedEntry;
      }
docs: EncodedEntryURI格式，其中 bucket+":"+key 称之为 entry
  
  @param bucket
  @param key
  @return UrlSafeBase64.encodeToString(entry)
  @link http://developer.qiniu.com/kodo/api/data-format