Serialize an existing Java object with circular dependencies

Question

I have an object from a class I cannot modify.

The object has a circular dependency.

I would like to serialize the object, but I don't have access to java source code, as it's in a library.

In C++ I could create a subclass, override the virtual methods, then cast down to get the desired behavior. In Java this is not possible.

What options do I have besides creating a new POJO class and copying over every field by hand?

You can use reflection and copy all fields recursively, while using an `IdentityHashMap` for resolving cycles. However, I'm sure, someone already did it: https://stackoverflow.com/a/5294224/581205 — maaartinus, Dec 30 '17 at 22:57

score 0 · Answer 1 · answered Dec 28 '17 at 23:24

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Serialization using Serializable is a bit smelly anyway. I'd prefer using an external serializer, using either JSON (e.g. Jackson, GSON) or a binary format (e.g. Kryo). Either way, you can write custom serializers in all of these that resolve your circular dependencies.

answered Dec 28 '17 at 23:24

Sean Patrick Floyd

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How do you resolve circular dependencies without annotating the class? – Andrew Prock Dec 29 '17 at 01:08
All of the technologies I listed support external serializers that resolve the dependencies externally. How you do it is up to you, but examples would be to serialize a List of Objects as a List of Object IDs, and deserialize it again by loading those objects by these IDs from your persistence layer – Sean Patrick Floyd Dec 29 '17 at 02:56
Do you have an example? – Andrew Prock Dec 29 '17 at 05:08
No, but those websites I linked to do. – Sean Patrick Floyd Dec 29 '17 at 17:25

score 0 · Answer 2 · answered Dec 28 '17 at 23:51

I'd opt for Jackson, even if you are going to be the only one reading/writing your objects. Many advantages, up to and including:

Diagnosing/debugging the serialized JSON makes life easy.
Staying on this well-trodden path means solutions to any questions are a Google away, e.g., http://www.baeldung.com/jackson-deserialization

Serialize an existing Java object with circular dependencies

2 Answers2