[hibernate-issues] [Hibernate-JIRA] Commented: (HBX-964) add serialVersionUID to entity classes

[jahlborn (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HBX-964?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=31220#action_31220 ] 

jahlborn commented on HBX-964:
------------------------------

i'll throw out a reason for adding a serialVersionUID: because the classes are broken without one.  Point "B)" in the first comment is not really true.  adding a serialVersionUID does not indicate that a class is serializable across versions.  that is indicated by maintaining the *same* serialVersionUID across multiple versions of the class.  as to my original point, a Serializable class without a serialVersionUID is broken because any serialized instance of that class are not guaranteed to be unserializable, ever.  serialVersionUID values are generated on the fly for classes without them, and a jvm is free to generate one however it likes.  so, today i generate a file with my serialized objects.  without touching my classes, i upgrade my jvm (needed a few bug fixes, or, hey, maybe i even switch jvm vendors) and suddenly i can no longer read any objects from that file.  

you should be generating the full serialVersionUID, and that will not imply that the class is serializable across versions because pretty much any change to the class will result in a new serialVersionUID (so the behavior will be correct by default).

> add serialVersionUID to entity classes
> --------------------------------------
>
>                 Key: HBX-964
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HBX-964
>             Project: Hibernate Tools
>          Issue Type: Improvement
>          Components: hbm2java
>    Affects Versions: 3.2beta10
>            Reporter: Dan Allen
>            Priority: Minor
>         Attachments: HBX-964-v1.txt
>
>   Original Estimate: 5 minutes
>  Remaining Estimate: 5 minutes
>
> The serialVersionUID is recommended for classes that implement java.io.Serializable.  The hbm2java task should either set the serialVersionUID to 1L or automatically generate a value. I prefer setting it to 1L because it is easy and it will work, but if you feel motivated, you can look at what Eclipse does to generate this value from the class signature.
> I have included a patch that just sets it to 1L.

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