[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-2586) Hibernate Serializable classes do not declare serialVersionUID

[Emmanuel Bernard (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-2586?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_30868 ] 

Emmanuel Bernard commented on HHH-2586:
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I am pretty sure Bloch did not say that all classes implementing Serializable should implement it, that would be pretty bad of him. At least in the second edition, he is not making such assertion.
We had a discussion on this subject (either on the dev list or in JIRA), the outcome was not to rush on manual magic numbers.

""
Please just remember that just because tools (like eclipse and others) warns about a missing serialversionUID it
does not mean it should be there. Simon Kicthing described it well in HBX-444:

"When you declare a serialVersionUID you're also declaring that you are aware of all the issues regarding serialising one version of a class and reimporting the serialized data into a different version of the class, and are promising to update the serialVersionUID whenever you make an *incompatible* change to the class.

However most people don't have a clue what is and what is not a serialization-incompatible-change to a class. In this situation I think the default behaviour (which is that the serialization mechanism declares incompatibility if *any* change occurs to the class) is much safer than having an auto-generated serialVersionUID on the class resulting in potientially corrupted objects on deserialization."
""

> Hibernate Serializable classes do not declare serialVersionUID
> --------------------------------------------------------------
>
>                 Key: HHH-2586
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-2586
>             Project: Hibernate3
>          Issue Type: Bug
>          Components: core
>    Affects Versions: 3.0 alpha, 3.0 beta 1, 3.0 beta 2, 3.0 beta 3, 3.0 beta 4, 3.0 rc 1, 3.0 final, 3.0.1, 3.0.2, 3.0.3, 3.0.4, 3.0.5, 3.1 beta 1, 3.1 beta 2, 3.1 rc 1, 3.1 rc2, 3.1 rc3, 3.1, 3.1.1, 3.1.2, 3.2.0.alpha1, 3.2.0.alpha2, 3.1.3, 3.2.0 cr1, 3.2.0.cr2, 3.2.0.cr3, 3.2.0.cr4, 3.2.0.cr5, 3.2.0.ga, 3.2.1, 3.2.2, 3.2.3
>         Environment: Not specific to any database, platform or Hibernate version.
>            Reporter: Manuel Dominguez Sarmiento
>   Original Estimate: 2 hours
>  Remaining Estimate: 2 hours
>
> None of the Serializable classes in Hibernate declare serialVersionUID (see http://www.hibernate.org/hib_docs/v3/api/serialized-form.html#org.hibernate.collection.AbstractPersistentCollection).
> This is recommended practice for ALL classes that implement the Serializable interface (see Joshua Bloch's Effective Java - Item #54). Adding these fields is trivial and takes little effort, but is a great enhancement if you are serializing Hibernate classes.
> For instance, we upgraded from Hibernate 3.2.2 to 3.2.3 in our production servers. We serialize process state (which sometimes includes references to Hibernate-managed entities) every 30 seconds or so and on shutdown, so in the event of failures or re-deployment, the processes can continue where they left off. We had a huge surprise when deserialization failed completely because AbstractPersistentCollection had slightly changed between the 3.2.2 and 3.2.3 releases, and this caused the automatically-generated default serialVersionUID to change, even though the changes in the serialized form are compatible as far as we can tell.

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