registering private inner classes

[ua stan]

Hi

how would I register class with kryo if it's private inner class? I'm getting this error 

Caused by: java.lang.IllegalArgumentException: Class is not registered: java.util.Collections$EmptyList

at com.esotericsoftware.kryo.Kryo.getRegisteredClass(Kryo.java:319)

at com.esotericsoftware.kryo.Kryo.writeClass(Kryo.java:374)

at com.esotericsoftware.kryo.serialize.FieldSerializer.writeObjectData(FieldSerializer.java:173)

... 35 more

[Martin Grotzke]

Hi,

you can use https://github.com/magro/kryo-serializers for this, it
provides several serializers for standard jdk classes, for
Collections.EMPTY_LIST there's the CollectionsEmptyListSerializer.

To register the serializer you have to add

kryo.register( Collections.EMPTY_LIST.getClass(), new
CollectionsEmptyListSerializer() );

Cheers,
Martin

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[ua stan]

Hi

Thanks for the help. However the question wasn't quite correct. Since this is my first try with Kryo I didnt figure out at first, this code does trick

kryo.register(Collections.EMPTY_LIST.getClass());

So standard serialized works out good. And this CollectionsEmptyListSerializer is for optimization, which is handy but not my goal right now.

Thank you

stan

[Martin Grotzke]

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Great it works for you,

cheers,
Martin

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[ua stan]

Hi

kryo complaints with message  Caused by: java.lang.IllegalArgumentException: Class is not registered: ...

How would you get over this if class in error message is package private, like in example below

Caused by: java.lang.IllegalArgumentException: Class is not registered: java.util.concurrent.locks.ReentrantLock$NonfairSync

[Martin Grotzke]

Hi,

this error pops up as the ReentrantLock is serialized using FieldSerializer.

You can write a custom serializer for ReentrantLock that correctly
handles this class and register this serializer for ReentrantLock at kryo.

I'd say that this is also a good idea as with the fieldserializer it
might happen that you serialize/deserialize it in a locked state, but
probably you'd expect such stuff to start "fresh" / unlocked when
deserialized.

Often the methods for java serialization (writeObject/readObject) in
such classes show you how to implement the custom serializer.

There's already a project that provides several serializers for standard
jdk types: https://github.com/magro/kryo-serializers
So this might also be a good home for a ReentrantLockSerializer if it
wouldn't make it into kryo itself.

Cheers,
Martin

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