code: @RequestMapping("/refund")
      public String refund(HttpServletRequest request){
          Map<String, String> receives = new HashMap<>();
  
          // TODO 这里还是建议直接从request中获取map参数，兼容支付宝修改或增减参数
          for (AlipayField f : AlipayFields.REFUND_NOTIFY){
              receives.put(f.field(), request.getParameter(f.field()));
          }
  
          logger.info("refund notify params: {}", receives);
          if (!alipayService.notifyVerifyMd5(receives)){
              System.out.println("refund sign verify failed");
              return "FAIL";
          }
  
          // TODO business logic
  
          logger.info("refund notify success");
          return "SUCCESS";
      }
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