解決辦法是前臺(tái)ajax需要添加contentType: "application/json;charset-UTF-8"

let data = [];
function determine() {
        //準(zhǔn)備ajax數(shù)據(jù)
        let group = {number,showTime,hiddenTime,times,interval};
        data.push(group);
    }
$.ajax({
            type: 'POST',
            url: '/control/startGroup',
            //轉(zhuǎn)換成json字符串
            data:JSON.stringify(data),
            dataType: 'json',
            contentType: "application/json;charset-UTF-8"
        });

因?yàn)楹蠖薐ava使用了@RequestBody

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

另

參考

@RequestBody和@RequestParam區(qū)別
https://www.cnblogs.com/hanszhao/p/10166277.html