Java Historian says: I was a reviewer for Effective Java 3rd Edition and EnumSet is the canonical example of the Serialization Proxy pattern, so I tried to make sure the pattern was implemented as perfectly as possible. 8192935: Fix EnumSet's SerializationProxy javadoc All of us who try to make java serialization work right have a mental model of the many things that might go wrong. Serialization of Class objects has never been part of my own mental model - I've only ever considered instances.
On Tue, Jun 18, 2019 at 5:32 AM Peter Levart <peter.lev...@gmail.com> wrote: > Hi, > > I recently stumbled on an exception thrown when deserializing stream > produced on JDK 8 and read with JDK 11. I narrowed the problem down to > serialization/deserialization of a public EnumSet.class object. There > were several changes made to EnumSet in the Mercurial history of jdk > repo, but I think the following two broke the serialization: > > http://hg.openjdk.java.net/jdk/jdk/rev/d0e8542ef650 > http://hg.openjdk.java.net/jdk/jdk/rev/a7e13065a7a0 > > It is interesting to note that before those two changes were made, there > was a chance to fix the problem reported by newly added serial lint > warnings. Unfortunately they were just silenced: > > http://hg.openjdk.java.net/jdk/jdk/rev/501d8479f798 > > +@SuppressWarnings("serial") // No serialVersionUID due to usage of > + // serial proxy pattern > > It is true that serialization of instances of Serializable classes is > not broken by changes to them when they implement serial proxy pattern > (i.e. writeReplace() method) even if they don't itself declare a private > static final long serialVersionUID field, but this is not true of Class > objects representing those Serializable classes. It is even more > controversial that serialization of Class objects representing > non-Serializable classes is never broken (which is understandable as > they don't have a habit of declaring serialVersionUID fields). > > Both of the above braking changes were made post JDK 8 release, so > deserialization of JDK 8 (and older) streams is affected in all JDK 9 + > releases or vice versa. > > So, what shall be done. I suggest adding serialVersionUID field to > EnumSet vith a value that corresponds to JDK 8 serialization format and > later backport this change to JDK 11. > > What do you think? > > > Regards, Peter > > > PS: ImmutableCollections nested classes also implement serial proxy > pattern and don't declare serialVersionUID fields, but they are not > public, so it is less chance that Class objects representing them could > be used in serial streams, although it is not impossible. For example: > > objectOutputStream.writeObject(Set.of().getClass()); > >
