Content type 'application/x-www-form-urlencoded;charset=UTF-8' not supported for @RequestBody XXX

解决办法是前台ajax需要添加contentType: "application/json;charset-UTF-8"

let data = [];
function determine() {
        //准备ajax数据
        let group = {number,showTime,hiddenTime,times,interval};
        data.push(group);
    }
$.ajax({
            type: 'POST',
            url: '/control/startGroup',
            //转换成json字符串
            data:JSON.stringify(data),
            dataType: 'json',
            contentType: "application/json;charset-UTF-8"
        });

因为后端Java使用了@RequestBody

public void controlGroup(@RequestBody List<GroupDTO> data) 

另

参考

@RequestBody和@RequestParam区别
https://www.cnblogs.com/hanszhao/p/10166277.html