Can a remote service return a remote object?

Question

Hi all,
please consider a business logic for a typical forum service :
public interface ForumManager extends Remote
Forum createNewForum(String Name);
Forum getForum(String Name);
public interface Forum extends Remote
void postNewArticle(String Title, String Content);
Article [] getArticles();
public class Article implements Serializable
There are two interfaces of remote objects: ForumManager and Forum, both of two interfaces are extended from interface Remote. I created two classes implementing these interfaces respectively, and created two stub classes from the implementation with rmic.
As the logic, a ForumManager creates and manages forums on the server. A client can retrieve a remote stub of a forum instance from the manager stub, and post articles to the forum stub. The forum stub then sends the new articles to the real ForumImpl on the server, and the real implementation of Forum on the server then save the articles into disks or DBs. So, you can see, the most important thing is that clients have to be able to get the stub of a forum.
Codes in createForum() of the implementation class of ForumManager is like this:
ForumImpl TheNewForum = new ForumImpl(this.getRef());
// ^ Because ForumImpl is a remote object, without a ref, it can not be marshaled.
ForumTable.put(Name, TheNewForum);
return TheNewForum;
The problem is, the Forum instance my client retrieved from FourmManagerImpl_Stub (gotten from Naming.lookup()) is a ForumImpl, but not a Forum_Stub. So that articles posted to the forum will not be sent to the server, and different clients can not share articles with each other. I found a bunch of documents about RMI, but they did not illustrated how to retrieve a stub of a remote object from another remote object (like a manager). If you know how to cope this problem, please tell me.
Edited by: DBPZ on Apr 2, 2008 3:33 AM

Answer 1

why does this base class exist?It's really only there to support stubs. The only thing it gives you over Object is the remote equality semantics, and only stubs need that. (It also provides the RemoteReference but only RMI needs that, internally, you don't.)
When should we use RemoteObject instead of UnicastRemoteObject?Never, but if you do, or you use Object (or indeed anything other than UnicastRemoteObject and Activatable), you have to export it yourself as indicated above.