Practical Guidelines for Java Serial Version ID and Serialization
Here are practical guidelines for using Java serialization and Serial
- Add Serial Version IDs to Your Classes Immediately
- How To Compute a Version ID
Add Serial Version IDs to Your Classes Immediately
You should add a Serial Version ID to your Serializable classes as
soon as you create them. This guarantees that if you make
changes to the class and save the class at different times that you
won't end up with different serial version IDs in the saved files.
For example, if you save a object of Class C version 1 (C1) which
doesn't have a version ID, then you modify it to version 2 (C2) and
save it, you'll have two saved files, one with C1 and one with C2
objects. At this point no matter what serial version ID you put in
the class, you will be unable to deserialize one of the saved files.
The caveat to versioning your Serializable classes is that you are
then restricted to making so-called "compatible" changes -- adding
fields or methods for example, but not removing fields or methods.
How To Compute a Version ID
serialver tool comes with Sun's Java Development Kit
(JDK). It take a full class name on the command line and returns the
serial version ID for that compiled class, or can be run with the
"-show" parameter to launch a small interactive GUI.
So if your class is
and you'll get output like this:
com.frequal.Foo: static final long serialVersionUID = -6618469841127325812L;
Take the code starting with "static" and place it inside your class
with other static variables. Now the serial version ID is locked in
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