Java Clone object using GSON

Question

I have to clone an object multiple times. My object is non serializable. I am using the following function

@SuppressWarnings("unchecked")
public static  T cloneThroughJson(T t) {
   Gson gson = new Gson();
   String json = gson.toJson(t);
   return (T) gson.fromJson(json, t.getClass());
}
// ...
Object cloned = cloneThroughJson(someObject);

I found that this is returning every time reference to the same object. e.g

Let's say I first call it for cloneThroughJson(x) it returns Y I again call it in the same function cloneThroughJson(x). And it again returns Y.

Do you know how to clone non serializable object in java using deep cloning?

Answer 1

It seems that it is a known issue. Your method will ONLY work if the copied object has a default no-argument constructor. In order to achieve what you want - you need to create an instance creator.

From documentation:

While deserializing an Object, Gson needs to create a default instance of the class Well-behaved classes that are meant for serialization and deserialization should have a no-argument constructor Doesn't matter whether public or private Typically, Instance Creators are needed when you are dealing with a library class that does NOT define a no-argument constructor

Instance Creator Example

private class MoneyInstanceCreator implements InstanceCreator<Money> {
  public Money createInstance(Type type) {
    return new Money("1000000", CurrencyCode.USD);
  }
}

Type could be of a corresponding generic type

• Very useful to invoke constructors which need specific generic type information
• For example, if the Id class stores the class for which the Id is being created.