关于前端传数据正常后端接收到为null的问题

问题遇到的现象和发生背景

问题相关代码，请勿粘贴截图

function getstatistics() {
        //ajax的post方式提交表单
        //$("#itemAddForm").serialize()将表单序列号为key-value形式的字符串
        $.post("/order/getStatistics", $("#statisticsForm").serialize(),
                function(data) {
                    console.log(data);
                    console.log($("#statisticsForm").serialize());
                    if (data.status == 200) {
                        $("#cancelSum").text(data.data.cancel.sum);
                        $("#cancelTotal").text("¥ " + data.data.cancel.total);
                        $("#okSum").text(data.data.complete.sum);
                        $("#okTotal").text("¥ " + data.data.complete.total);
                    } else {
                        $.messager.alert(data.msg);
                    }
                });
    }

@RequestMapping(value = "/getStatistics")
    public Result getStatistics(Map<String, Object> params) throws ParseException {

        // 查取消 未付款取消
        System.out.println(params.get("startDate"));
        params.put("status", OrderConstant.CANCEL_NO_PAY);
        Statistics CANCEL_NO_PAY = orderMainService.getStatistics(new Query(params));

        // 查取消 付款后取消
        params.put("status", OrderConstant.CANCEL_PAY);
        Statistics CANCEL_PAY = orderMainService.getStatistics(new Query(params));

        Statistics cancel = new Statistics();
        cancel.setSum(CANCEL_NO_PAY.getSum() + CANCEL_PAY.getSum());

        double c1 = Double.parseDouble(CANCEL_NO_PAY.getTotal() == null ? "0" : CANCEL_NO_PAY.getTotal());
        double c2 = Double.parseDouble(CANCEL_PAY.getTotal() == null ? "0" : CANCEL_PAY.getTotal());
        cancel.setTotal(PIPIUtils.formatMoney(String.valueOf(c1 + c2)));

        // 查完成
        params.put("status", OrderConstant.COMPLETE);
        Statistics complete = orderMainService.getStatistics(new Query(params));
        complete.setTotal(complete.getTotal() == null ? "0" : PIPIUtils.formatMoney(complete.getTotal()));

        Map<String, Statistics> map = new HashMap<String, Statistics>();
        map.put("cancel", cancel);
        map.put("complete", complete);


        return Result.ok(map);
    }

}

我的解答思路和尝试过的方法

我想要达到的结果

在传之前先检查一下是否能正常打印

加@RequestBody

public Result getStatistics(@RequestBody Map<String, Object> params) 

f12打开控制台，在network里看下你到底传了什么东西

后台接收为null，解决：设置ajax的content-type为application/x-www-form-urlencoded