如何将 JSON 中 Java 对象的实例类型发送到 Java Spring-Server Post 请求？

Question

I have a baseclass and three extending classes. For example:

BaseClass:

public BaseClass {
 int id;
} 

public SubClass extends BaseClass {
 int sub1;
}

public SubClass2 extends BaseClass {
 int sub2;
}

Now i want to send a json file to my spring server and the server must check if it is a SubClass-type or a SubClass2-type

    @PostMapping(value = "/test", consumes = MediaType.APPLICATION_JSON_VALUE, produces = MediaType.APPLICATION_JSON_VALUE)
    public ResponseEntity<?> create(@RequestBody List<BaseClass> entry);

sending JSON:

{
    "id": 1,
    "sub1": 1
},
{
    "id": 2,
    "sub2": 2
}

I except a List of BaseClasses but try to cast them in the specific subclass. How can i do this? Following did not work.

if (abc instanceof SubClass) {
                log.info("abc is instance of SubClass");
} else if (abc instanceof SubClass2) {
                log.info("abc is instance of SubClass2");
} 

Answer 1

If you will accept BaseClass Spring will map your json to be compliant with only BaseClass ignoring all the other fields. So your check for subclasses will not work at all.

The simplest solution is to accept data as plain text and after that manually try to map it to your models using GSON or something similar like this

new Gson().fromJson("{
    "id": 1,
    "sub1": 1
}", SubClass.class);

But it is a bad way to handle this. Your approach need to be changed architecturally. The simplest way to do it is to introduce data field to you model like this

{
    "id": 1,
    "data": {
         "key": "sub1",
         "value": 1
     },
},

public Data {
 String key;
 int value
} 

public BaseClass {
 int id;
 Data data;
} 

this way you will be able to check

if (abc.data.key.equals("sub1")) {
                log.info("abc is sub1");
} else if (abc.data.key.equals("sub1")) {
                log.info("abc is sub2");
} 

This will require a bit more complex further implementation, but it will work.

Hope it helps.