ClassCastException: java.util.HashMap cannot be cast to mypackage.MyLinkedHashMap

[navigateur]

I have a class:

{code}
@Portable(aliasOf=Map.class)
class MyLinkedHashMap extends LinkedHashMap<Something, SomethingElse> {
...
{code}

and I get:

{code}ClassCastException: java.util.HashMap cannot be cast to mypackage.MyLinkedHashMap{code}

...upon trying to return one of these from the server side (but not during marshaller generation). I'm using 2.1.0.Beta1 and I'm not sure if this would've worked in previous versions.

I was previously advised I should use List.class as an alias for a LinkedHashMap implementation to preserve ordering but that gives an invalid type error (cannot convert) during marshaller generation. The same is true for LinkedHashSet, which I also need.

Solution?

[jfuerth]

Unfortunately, this is the way the aliasing facility works in Errai Marshalling: "aliases do not inherit functionality."

The Map marshaller always produces an instance of HashMap when it's demarshalling. Since you have aliased MyLinkedHashMap to Map, you will always get back a HashMap when demarshalling. Not what you want, I know.

If you can do away with the custom subclass, that would be easiest. Errai Marshalling preserves map ordering for field types java.util.LinkedHashMap and java.util.SortedMap.

Otherwise, you will have to create a custom marshaller for MyLinkedHashMap. It's not so bad, because you can extend MapMarshaller. Use LinkedMapMarshaller as your guide:

https://github.com/errai/errai/blob/master/errai-marshalling/src/main/java/org/jboss/errai/marshalling/client/marshallers/LinkedMapMarshaller.java

Hope that helps,

Jonathan

[navigateur]

I'll try that out.

Are there any plans to make this unnecessary? I like subclassing as I've other related functionality & variables. And there are quite a few so I'd have to bloat my code a tiny bit, maybe, with a custom marshaller for each, right? Ideally I'd just be able to do @Portable class MyLinkedHashSet extends LinkedHashSet but I don't know if that'll ever be possible.

[navigateur]

Hi, subclassing MapMarshaller wasn't possible for my custom LinkedHashMap since MapMarshaller is type-bound to a Map<Object, Object>, and my custom one had specified key & value types. Otherwise, where would I need to place the custom marshaller to make it work? Anywhere in my project? Has errai been updated to allow direct marshalling of subclasses of LinkedHashMap since I first asked this?