如何实现将实体对象还有List同时放到一个json数据中

Question

User user = userService.getById(id);
ArrayList list= moneyService.getList(id);

如何将user 还有 list放到一个json中呢

{
"user": {
"id": "1",
"name": "张三"
},
"monylist": [{
"id": "444",
"num":"300"
}, {
"id": "444",
"num":"400"
}]
}

求帮助