Subclass in a field with a concrete type is written, and then dropped on read

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Dal 16/10/2026.

Valutazione

Difficoltà
4/5
Tempo stimato
1-2 giorni
Idoneità per principianti
50/100
Tipo di issue
Bug
Chiarezza
Abbastanza chiara
Stato di attività
Attiva
Stack tecnologico
java
Ambito
backend

Direzione di ricerca

Start with the Java JSON serialization and deserialization paths exercised by the provided ForyJson example, then compare their handling of a concrete declared field whose runtime value is a subclass with the binary module’s behavior. Reproduce the example and trace how the JSON reader chooses the field type. Done means it either preserves the subclass and its breed field or reports clearly that writing would discard subclass data.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

bug
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  • I had searched in the issues and found no similar issues.
Version

1.7.7

Component(s)

Java

Minimal reproduce step

A field has a declared type. The declared type is a concrete class, and the class is not final. The value is an instance of a subclass.

Version 1.7.7 writes the fields of the subclass, which 1.7.6 did not. The read operation still builds the declared type and ignores those fields. The data is therefore in the document, and nothing can read it. Fory gives no error at either step.

import org.apache.fory.Fory;
import org.apache.fory.config.Language;
import org.apache.fory.json.ForyJson;

public class SubclassStateDropped {

    public static class Animal {
        String name = "generic";
        public String toString() { return "Animal(name=" + name + ")"; }
    }

    public static class Dog extends Animal {
        String breed = "lab";
        public Dog() { name = "rex"; }
        public String toString() { return "Dog(name=" + name + ", breed=" + breed + ")"; }
    }

    public static class Owner {
        private Animal pet = new Dog();
        public Owner() { }
        public String toString() { return "Owner(pet=" + pet + ")"; }
    }

    public static void main(String[] args) {
        Owner original = new Owner();

        ForyJson json = ForyJson.builder().withFieldMode(true).build();
        byte[] doc = json.toJsonBytes(original);
        System.out.println("fory-json wrote : " + new String(doc));
        System.out.println("fory-json read  : " + json.fromJson(doc, Owner.class));

        Fory core = Fory.builder().withLanguage(Language.JAVA).requireClassRegistration(false).build();
        System.out.println("fory-core read  : " + core.deserialize(core.serialize(original)));
    }
}
What did you expect to see?

One of two results.

In the first result, fory-json reads the document it wrote and gives Owner(pet=Dog(name=rex, breed=lab)). The binary module gives this result for the same object, as the third line of the output shows, so it is the behaviour the project has already established.

In the second result, fory-json refuses the write operation. The error message tells the user that the runtime type is a subtype of the declared type, and that a write operation discards data.

Fory JSON has no open polymorphism, and we know that this is a design decision. That makes the second result the one we expected. In both results the application can find that Fory made a decision.

What did you see instead?

Owner(pet=Animal(name=rex)), and no error from either step.

The document holds "breed":"lab". The value of name is "rex", which the constructor of Dog assigns, so the object written was the Dog. The read operation builds an Animal and ignores breed. No part of the API tells the application that the field was discarded.

Anything Else?

No response

Are you willing to submit a PR?
  • I'm willing to submit a PR!
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