JsonTypeInfo.As.EXISTING_PROPERTY does not seem to work while serializing an object

[shrey-garg]

Hi,

I am trying to serialize an object into json so that I can send the type info in an existing field of the class. I am using v2.6.2 and also tried using 2.8.x, but the problem still persists.

    B b = new B();
    b.setSomething("Test");
    String o = JSONObjectMapper.getObjectMapper().writeValueAsString(b);
    System.out.println(o);
    String s = "{ \"type\":\"B\", \"something\":\"else\" }";
    A a = JSONObjectMapper.getObjectMapper().readValue(s, A.class);
    System.out.println(a instanceof B);

Class A:

    @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "type")
    @JsonSubTypes({
            @JsonSubTypes.Type(value = B.class, name = "B")
    })
    public abstract class A {
          public String type;

          public String getType() {
                return type;
          }

          public void setType(String type) {
                this.type = type;
          }
   }

Class B:

    public class B extends A {
            private String something;

            public String getSomething() {
                   return something;
             }

           public void setSomething(String something) {
                   this.something = something;
           }
    }

The output of the above program is:

    {"something":"Test","type":null}
    true

The type field is not being set when serializing but it's being recognized while deserializing the Object.

If I change EXISTING_PROPERTY to PROPERTY, it's working as expected and adding "type" twice, once with the info and once without.

[kulabun]

B b = new B();
b.setSomething("Test");
String o = JSONObjectMapper.getObjectMapper().writeValueAsString(b);
System.out.println(o);
String s = "{ \"type\":\"B\", \"something\":\"else\" }";
A a = JSONObjectMapper.getObjectMapper().readValue(s, A.class);
System.out.println(a instanceof B);

Where do you set property "type" for b? Nowhere, so it is null. Existing property used, so providing valid value is your responsibility.

The type field is not being set when serializing

Do you mean serializer have to set it for your bean? Change it's state? The one and only responsibility of serializer is extract your data and output it to specified format. That it what it does.

[shrey-garg]

Where do you set property "type" for b? Nowhere, so it is null. Existing property used, so providing valid value is your responsibility.

Do you mean serializer have to set it for your bean? Change it's state? The one and only responsibility of serializer is extract your data and output it to specified format. That it what it does.

Thanks for the clarification, makes sense.