是否可以在运行时获取Java类的serialVersionUID

Question

It's well known that runtime will genereate serialVersionUID field for your class, if you failed to explicitly define it.

But is it possible to get this value in runitme? Is it possible in runtime, having reference to .class , obtain it's serialVersionUID ?

Answer 1

 Integer i = new Integer(5);
 long serialVersionID = ObjectStreamClass.lookup(i.getClass()).getSerialVersionUID();

Above is the sample code to get serial version id of the class at runtime.

Answer 2

What I want: to force my code [to] change serialVersionUID automatically ... when I change internal structure of these classes.

No you don't. You want to keep the serialVersionUID the same forever, and to restrict the internal changes to what can be handled automatically by Serialization, for which you need to consult the Versioning chapter of the Object Serialization Specification. Changing the serialVersionUID on every class change is an urban myth which unfortunately has been far too widely propagated and accepted.

And your proposed solution won't work either. 'Skipping deserialization instances of old versions of [a] class' isn't a solution to anything. Serialization will already have rejected it with an exception if the serialVersionUIDs don't agree. Anything you do after that is already too late.

This is sounding like an XY problem. You want to do X, you think Y is the answer, so you ask about Y, when you should be asking about X. For the correct solution see above.

Answer 3

Sure you can. serialVersionUID is a regular static variable, so you can access it when you want. The only problem is that it is typically defined as private or protected , so you can access it from the class itself only. To access it from outside you can use reflection:

Class<?> clazz = obj.getClass();
Field f = clazz.getDeclraredField("serialVersionUID");
f.setAccessible(true);
long uid = (long)f.getValue();