[Java] Component types on generic arrays are lost during (de-)serialization

[mtf90]

Search before asking

• I had searched in the issues and found no similar issues.

Version

• 0.5.0-SNAPSHOT from the nightly builds (current HEAD is a80dce6)
• OS: Linux x64
• Java: fails on JDK 11/17/21

Component(s)

Java

Minimal reproduce step

public class App {

    public static void main(String[] args) {
        final Fury fury = Fury.builder().requireClassRegistration(false).build();
        final ArrayWrapper<String> wrapper = new ArrayWrapper<>(String.class, 2);

        wrapper.array[0] = "Hello";

        final byte[] bytes = fury.serialize(wrapper);
        final ArrayWrapper<String> deserialized = (ArrayWrapper<String>) fury.deserialize(bytes);

        deserialized.array[1] = "World";
    }

    static class ArrayWrapper<T> {

        private final T[] array;

        public ArrayWrapper(Class<T> clazz, int capacity) {
            this.array = (T[]) Array.newInstance(clazz, capacity);
        }
    }
}

What did you expect to see?

A successfull run of the program

What did you see instead?

Exception in thread "main" java.lang.ClassCastException: class [Ljava.lang.Object; cannot be cast to class [Ljava.lang.String; ([Ljava.lang.Object; and [Ljava.lang.String; are in module java.base of loader 'bootstrap')

Anything Else?

It appears that the information about the component type (here String.class) are lost and the (de-) serializer simply assumes "Generic Type? => Object!". The problem here is that one cannot simply replace the Array.newInstance(clazz, capacity); with new Object[capacity]; because then the wrapper.array[0] = "Hello"; statement fails with the same error.

Are you willing to submit a PR?

• I'm willing to submit a PR!

[chaokunyang]

Thanks @mtf90 , I can reproduce this bug locally. This is a bug in fury. Fury take Object[] as a final type, it skip writing class info for such types, so the deserialization got wrong type. I fixed it in #1324. Thanks again for reporting this bug.

[mtf90]

Seems like fury is not only blazing fast with serialization but also with bug fixes 😆. Thank you very much for the quick response. Looking forward to test the nightly once this is merged.