2021-09-22_token `jsontoken.start_object`

json之list参数传给springboot,4点内容

1.参考文章https://blog.csdn.net/qq_44865979/article/details/118091997

2.错误提示：JSON parse error: Cannot deserialize value of type java.util.ArrayList<实体类> from Object value (token JsonToken.START_OBJECT)

json对象转换成Java对象时，发生错误。可能的原因是json数据的写法出错了。

3.json数据中的属性对应的是java实体类的属性，而不是参数名字。也就是参数名不应该出现在json数据中。

例如：

User对象包含username,userage,userpwd 3个属性
1.public  ResponseBean insertUser(@RequestBody User newUser)
json是{"username":"...","userage":"...","userpwd":"..."}
2.public  ResponseBean insertUser(@RequestBody List<User> userlList)
json是[
{"username":"...","userage":"...","userpwd":"..."},
{"username":"...","userage":"...","userpwd":"..."},
 ...
]
而不是{
    "UserlList":[
               {"username":"...","userage":"...","userpwd":"..."},                     
               {"username":"...","userage":"...","userpwd":"..."},
                ...
                ]
   }
Scloolclass对象包含classId,className,list<User> userlList 3个属性
3.public  ResponseBean insertScloolclass(@RequestBody Scloolclass sc)
json是{
    "classId":"...",
    "className":"...",
    "userlList":[
               {"username":"...","userage":"...","userpwd":"..."},                     
               {"username":"...","userage":"...","userpwd":"..."},
               ,...
                ]
}
    
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4.如果不知道json数据的写法时，可以先在后台向前台输出json数据，然后通过观察，发现json数据的写法。

例如

    @PostMapping(value = "/insertSchedule",produces = "application/json;charset=UTF-8")
    //不知道List<Schedule_detail> detailList参数的json格式。
    public  ResponseBean insertSchedule(@RequestBody List<Schedule_detail> detailList){
        for (Schedule_detail sd:detailList) {
            System.out.println(sd);
        }
        return new ResponseBean(200,"success",detailList);
    }
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@PostMapping(value = "/insertSchedule",produces = "application/json;charset=UTF-8")
   // 后台输出List<Schedule_detail> detailList参数的json格式
    public  ResponseBean insertSchedule(){
        List<Schedule_detail> detailList = new ArrayList<Schedule_detail>();
        Schedule_detail s1= new Schedule_detail();
        s1.setSch_detail_id(1);
        Schedule_detail s2= new Schedule_detail();
        s1.setSch_detail_id(2);
        
        detailList.add(s1);
        detailList.add(s2);
        
        for (Schedule_detail sd:detailList) {
            System.out.println(sd);
        }
        return new ResponseBean(200,"success",detailList);
    }
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输出结果为：可以看出List<Schedule_detail> detailList参数的json格式是[{},{}…]，
而不是{“detailList”:[{},{},…]}

{
    "code": 200,
    "msg": "success",
    "data": [
        {
            "sch_detail_id": 1,
            "course_id": null,
            "course_name": null
        },
        {
            "sch_detail_id": 2,
            "course_id": null,
            "course_name": null
        }
    ]
}
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