[Simple-support] How can I serialize an unmodifiable list?

[Lecomte, J-F. <JFL...@rh...>]

I get a < NoSuchMethodException > when I try to serialize a list that is wrapped by Collections.unmodifiableList(...) or a list obtained by Arrays.asList(...). The same applies to UnmodifiableList from Google's Guava library.

Here is a snippet that exposes the problem:

public class Main
{
    public static void main(final String[] args) throws Exception
    {
        final ArrayList<Integer> arrayList = new ArrayList<Integer>(Arrays.asList(1, 2, 3, 4));

        testLoadSave(new ObjectToPersist(arrayList)); // Will be successful
        testLoadSave(new ObjectToPersist(Collections.unmodifiableList(arrayList))); // Will throw a NoSuchMethodException
        testLoadSave(new ObjectToPersist(Arrays.asList(5, 6, 7, 8)));
    }

    private static void testLoadSave(final ObjectToPersist objectToPersist) throws Exception
    {
        final Serializer serializer = new Persister();

        final ByteArrayOutputStream out = new ByteArrayOutputStream();
        serializer.write(objectToPersist, out);

        final ByteArrayInputStream in = new ByteArrayInputStream(out.toByteArray());
        final ObjectToPersist objectRead = serializer.read(ObjectToPersist.class, in);

        System.out.println(objectRead);
    }

    public static class ObjectToPersist
    {
        @ElementList(name = "myList", entry = "element")
        private final List<Integer> _myList;

        public ObjectToPersist(
            @ElementList(name = "myList", entry = "element") final List<Integer> myList)
        {
            _myList = myList;
        }

        public List<Integer> getMyList()
        {
            return _myList;
        }

        @Override
        public String toString()
        {
            final StringBuilder builder = new StringBuilder();
            builder.append("ObjectToPersist@");
            builder.append(hashCode());
            builder.append("[_myList=");
            builder.append(_myList);
            builder.append("]");
            return builder.toString();
        }
    }
}


I don't really care about the exact type of the list stored in my object, but I would like to keep it unmodifiable. So far I fixed the problem by modifying "ObjectToPersist" class this way:

        public ObjectToPersist(
            @ElementList(name = "myList", entry = "element") final List<Integer> myList)
        {
            _myList = new ArrayList<Integer>(myList);
        }
        public List<Integer> getMyList()
        {
            return Collections.unmodifiableList(_myList);
        }


But this implies creating a new ArrayList all the time. I would prefer something like this:

        public ObjectToPersist(
            @ElementList(name = "myList", entry = "element") final List<Integer> myList)
        {
            if (myList is already immutable)
                _myList = myList;
            else
                _myList = new ArrayList<Integer>(myList);
        }
        public List<Integer> getMyList()
        {
            return _myList;
        }

Using ImmutableList from Google's Guava library, I could do just this (ImmutableList.copyOf(...)), but it won't serialize... I was wondering if there was a way to support those immutable collections with SimpleXML...

Thanks!
JFL