code: public static String join(String[] strings, String separator) {
          if (strings == null || strings.length == 0) {
              return EMPTY;
          }
          StringBuilder sb = new StringBuilder();
          for (String string : strings) {
              if (isNotBlank(string)) {
                  sb.append(string).append(separator);
              }
          }
          return sb.length() > 0 ? sb.substring(0, sb.length() - separator.length()) : StringUtils.EMPTY;
      }
docs: 连接字符串数组
  
  @param strings   字符串数组
  @param separator 分隔符
  @return 按分隔符分隔的字符串