How to set Unmodifiable collection serializer of Kryo in Spark code

Question

I am using Kryo serialization in Spark (v1.6.1) in Java and while serializing a class which has a collection in its field, it throws the following error -

Caused by: java.lang.UnsupportedOperationException
         at java.util.Collections$UnmodifiableCollection.add(Collections.java:1055)
         at com.esotericsoftware.kryo.serializers.CollectionSerializer.read(CollectionSerializer.java:102)
         at com.esotericsoftware.kryo.serializers.CollectionSerializer.read(CollectionSerializer.java:18)
         at com.esotericsoftware.kryo.Kryo.readObject(Kryo.java:648)
         at com.esotericsoftware.kryo.serializers.FieldSerializer$ObjectField.read(FieldSerializer.java:605)
         ... 27 more

I found out that this is because the default CollectionSerializer of Kryo can not deserialize the collection, because its not modifiable and we should use UnmodifiableCollectionsSerializer instead.

How do I mention specifically in spark code to use UnmodifiableCollectionsSerializer for Kryo?

My current configuration is -

SparkConf conf = new SparkConf().setAppName("ABC");
conf.set("spark.serializer", "org.apache.spark.serializer.KryoSerializer");
conf.registerKryoClasses(new Class<?>[] {*list of classes I want to register*});

Stoned

Answer 1

In case anybody else face this issue, here is the solution - I got it working by using javakaffee kryo serializers.

Add the following maven dependency:

<dependency>
        <groupId>de.javakaffee</groupId>
        <artifactId>kryo-serializers</artifactId>
        <version>0.42</version>
</dependency>

Write a custom kryo registrator to register UnmodifiableCollectionsSerializer

    public class CustomKryoRegistrator implements KryoRegistrator {
        @Override
        public void registerClasses(Kryo kryo) {        
             UnmodifiableCollectionsSerializer.registerSerializers(kryo);
        }
   }

Set spark.kryo.registrator to the custom registrator's fully-qualified name

conf.set("spark.kryo.registrator", "com.abc.CustomKryoRegistrator");

References -

https://github.com/magro/kryo-serializers

Spark Kryo: Register a custom serializer

Stoned

Thanks Pooja Mazumdar . This solution worked like charm !! – Homoousian