code: public static String paramsToString(String charset, String... params) {
          StringBuffer sb = new StringBuffer();
          try {
              for (int i = 0; i < params.length - 1; i = i + 1) {
                  sb.append("&");
                  sb.append(URLEncoder.encode(params[i], charset));
                  sb.append("=");
                  sb.append(URLEncoder.encode(params[i + 1], charset));
              }
          } catch (UnsupportedEncodingException e) {
              e.printStackTrace();
          }
          return sb.substring(1);
      }
docs: convert parameters to string
  
  @param charset
  编码
  @param params
  parameter
  @return 拼接后的字符串