Java 关于反序列化继承 class 的一些问题

Question

When I tried to send a object from postman to restcontroller, it couldnnot deserialize as expected. My code:

BaseClass:

@Data
@MappedSuperclass
@NoArgsConstructor
@AllArgsConstructor
@SuperBuilder
public class BaseClass  implements Serializable{

    private static final long serialVersionUID = -93167525523223059L;
    
    private String id;

}

User:

@Data
@NoArgsConstructor
@AllArgsConstructor
@SuperBuilder
public class User extends BaseClass{

    private static final long serialVersionUID = -93167525523563033L;
    
    private String name;
    
    private String email;
   
    // ...other fields
}

@Data
@NoArgsConstructor
@AllArgsConstructor
@SuperBuilder
public class Group extends BaseClass{

    private static final long serialVersionUID = -93167115523563033L;
    
    private String name;
    
    private Set<User> users;

    // ...other fields
}

RestController

    @PutMapping("/{id}")
    public void updateGroup(@PathVariable String id, @RequestBody Group group) {
        // some code @debug// 
        return null;
    }

When I made a request using Postman, my request body was:

{
    "id": "group1",
    "users": [
    {
        "id": "user1"
    },
    {
        "id": "user2"
    },
    {
        "id": "user3"
    }]
}

I debuged in @debug and find that the @RequestBody group had only a user{id=user1}

I did some research and knew one solution. If I changed the request body to

{
    "id": "group1",
    "users": [
    {
        "id": "user1",
        "name": "name1"
    },
    {
        "id": "user2",
        "name": "name2"
    },
    {
        "id": "user3",
        "name": "name3"
    }]
}

It worked. And I found that, it seems, when deserializing, the key to identify user is the (name, email), in the User, not the id, in the BaseClass. So my question is, is it what I think right? If so, how to change my code to get three users when I only deliver the id. In my current project, User has a lot properties, so I just want to send some few fields, not all. So I don't want to send the name, email and other fields.

Answer 1

By default, the json deserialization process considers all the attributes of a class to be present in the given json string. If there is a need for only specific attributes and if rest of them are to be made optional, then javax.annotation.Nullable annotation can be used for non-mandatory attributes something like this:

public class User extends BaseClass {
    private String name;

    @Nullable
    private String email;
    /*..*/
}

Further more, in order to have a fine control on the object hierarchy you can also make use of Jackson Library and define your object hierarchy as below:

Base class:

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "id")
@JsonSubTypes(value = {
    @JsonSubTypes.Type(name = "group", value = Group.class),
    @JsonSubTypes.Type(name = "user", value = User.class)})
public class BaseClass {
    private String id;
}

Sub classes:

@JsonTypeName(value = "user")
public class User extends BaseClass {
    /*..*/
}

@JsonTypeName(value = "group")
public class Group extends BaseClass {
    /*..*/
}