kryo5 upgrade

[Aklakan]

GitHub issue resolved (no issue created yet).

Pull request Description: Upgrade to kryo5. Need yet to test whether spatial indexes created with kryo4 can be loaded with kryo5. Also, there was an inconsistent use of ConcurrentHashMap and LinkedHashMap that was revealed when a test case failed with kryo5.
In my first experiments I was not able to load a spatial index created with kryo4 using kryo5.

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See the Apache Jena "Contributing" guide.

[Aklakan]

I was not able to load a spatial-index created with kryo4 using kryo5 - it fails to deserialize the ConcurrentHashMap whose registration was missing. Kryo4 auto-registered classes in that case, whereas kryo5 by default requires registration. There is a flag kryo5.setRegistrationRequired(false); but this does not make loading work.

The question is whether to schedule a kryo5 upgrade for Jena6.

[afs]

The question is whether to schedule a kryo5 upgrade for Jena6.

Probably, yes. It is safer.

A major version change to Jena comes every 2 years when the supported java version changes so the opportunity is now.

Running both, while possible, is a maintenance cost.

Even if Kryo4 works now, bug fixes and security fixes will likely be to kryo5 first. I don't see much development around kryo4.

Choosing Kryo5 does not impact applications using Kryo4 elsewhere in their codebase.

[afs]

No rush - trying to get all the "bumps" done early in the 6. cycle,; this one is isolated so not getting in the way of anything outside of geosparql - can this merged now or are there other changes necessary?

[Aklakan]

There are a couple of small QoL improvements that I should add to avoid confusion.

I think it is still possible to read the metadata (from kryo's perspective a plain string) of spatial indexes created with kryo4 using kryo5.

• If so, then i can add a check whether the version field is 2.0.0 and raise an exception that this format is no longer supported. Deleting the spatial index file should re-create it on Fuseki start up.
• I should use a different version value for kyro5 in the metadata, such as 3.0.0.

[Aklakan]

I added the version check - with an old index it now outputs:

org.apache.jena.geosparql.spatial.SpatialIndexException: Spatial index version 2.0.0 is no longer supported.
Move or delete this file to allow for creation of a new index in its place: /foo/bar/spatial.index
	at org.apache.jena.geosparql.spatial.index.v2.SpatialIndexIoKryo.load(SpatialIndexIoKryo.java:219)