How to deserialize an object persisted in a db now when the object has different serialVersionUID

Question

My client has an oracle data base and an object was persisted as a blob field via objOutStream.writeObject, the object now has a different serialVersionUID (eve

Answer 1

If you've got multiple versions of the class stored in the database, it might be pretty tricky to deserialize and upgrade them all to a consistent serialization format in a single pass.

If possible, you might alter the table with a column to flag whether the serialized object has been processed yet. Then make passes over the table for each serialVersionUID, where you try to process any objects that haven't been dealt with yet. You can catch the InvalidClassException and go on to the next record if your updater encounters a serialized object that it doesn't handle, making a note of the version number so that you can make another pass.

This is a little tedious, but very simple.

Java serialization has some very nice features to support evolution of classes. However, you have to be aware of what you are doing. It may be that all of the objects actually have the same data, but no attention was paid to maintaining the version ID.

You could continue to use serialization once you get all of the objects updated to the same version. Just be careful as you add new fields to the class that they make sense with their default values (booleans are false, Objects are null, ints are zero, etc).