Spring Boot Jackson Databind - Configure Inheritance

Question

Suppose I have a base class A:

public class A {
    public String a;
}

And two child classes B and C:

public class B extends A {
    public String b;
}

public class C extends A {
    public String c;
}

And wrapper of A class:

public class Wrapper {
    public A a;
}

And I have Rest controller that receives client requests as wrapper object:

@RestController
public class SomeController {

    public void foo(@RequestBody Wrapper wrapper) {}

}

The problem is that Jackson casts wrapper field to base class A.

How can I configure it to recieve correct type?

https://github.com/FasterXML/jackson-docs/wiki/JacksonPolymorphicDeserialization — shmosel, May 25 '18 at 01:49
@shmosel I'm having such [error](https://stackoverflow.com/questions/6435062/jackson-deserialization-unexpected-token-end-object) — ivanjermakov, May 25 '18 at 02:13

score 1 · Accepted Answer · answered May 25 '18 at 15:14

Annotate your base class A with type information that tells Jackson how to decide whether a given json object should be deserialized to B.java or C.java.

Ex: With the below code, we are telling jackson that json object for A.class will contain a property with key type whose value can be either "b" or "c". If the value is "b", deserialize the object to B.class, else deserialize it to C.class

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type")  
@JsonSubTypes({  
    @Type(value = B.class, name = "b"),  
    @Type(value = B.class, name= "c")
    })  
class A {
}

Following is the json that you should be using.

{
   "a" : { // This will be deserialized to B.class
      "type": "b",
      // field of B.class
   }
}



{
   "a" : { // This will be deserialized to C.class
      "type": "c",
      // field of C.class
   }
}

I got it right but important thing was that base class cannot be instantiated. Base class should be `abstract` or `interface`. — ivanjermakov, May 26 '18 at 17:38

Spring Boot Jackson Databind - Configure Inheritance

1 Answers1