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Java Custom Serialization

Asked 2011-09-03T02:29:10.120
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I have an object that contains a few unserializable fields that I want to serialize. They are from a separate API that I cannot change, so making them Serializable is not an option. The main problem is the Location class. It contains four things that can be serialized that I'd need, all ints. How can I use read/writeObject to create a custom serialization method that can do something like this:

// writeObject:
List<Integer> loc = new ArrayList<Integer>();
loc.add(location.x);
loc.add(location.y);
loc.add(location.z);
loc.add(location.uid);
// ... serialization code

// readObject:
List<Integer> loc = deserialize(); // Replace with real deserialization
location = new Location(loc.get(0), loc.get(1), loc.get(2), loc.get(3));
// ... more code

How can I do this?

java serialization
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If it must be Java serialization, the only way I know of is to redefine the readObject() and writeObject() in all classes having a reference to an instance of Location as shown in Momo's answer. Note that this will not allow you to serialize a Location[], and require you to subclass all Collection<Location> appearing in your code. Moreover, it requires the fields of type Location to be marked transient, which will exclude their definitions from being written to the serialization stream, possible foiling the detection of incompatible class changes.

A better way would be to simply override ObjectOutputStream.writeObject. Alas, that method is final. You could override ObjectOutputStream.writeObjectOverride() instead, but that method can not delegate the default implementation, ObjectOutputStream.writeObject0() because that method is private. Of course, you could invoke the private method using reflection, but ...

Therefore, I recommend verifying your constraints. Does it have to be Java serialization? Can you really not change the definition of class Location?

If you have the source code to class Location, it's quite trivial to add implements Serializable and add it to your classpath. Yes, you'll have to do this again whenever you upgrade the library, but it might be better than the alternative ...

answered 2011-09-03T07:56:31.237

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