DWR

Suppose you want to create a method that can return generic "database rows" from server to client.
A DWR method with this signature can be created to accomplish this task:

public Map<String, Object> getRowsFromDb();

now if you then need to return updated date back from client to server, another method can be created with this signature:

public void updateData(Map<String, Object> data);

The problem is that DWR can convert Map<String, Object> to JSON, but cannot convert JSON back to Map<String, Object>.
Considering the informations contained in JSON, DWR should be able at least to convert incoming JSON to String, Boolean, float, or Map.

For more info refer to thread "Passing parameters of type Map<String, Object>" in the DWR mailing list.