Spring Webflow integration with Spring MongoDB issues

[marcovmx]

Hi, I wrote a custom ConversationManager having a Repository object using a MongoTemplate. I am getting a NullPointerException when storing the FlowExecution object, the reason is 'messagesMemento' contains LinkedHashMap entry containing a null key ({null=[]}). The exception is thrown when SpringMongo tries to call getClass() on that null key. It makes no sense to store a null key entry for one side and for another, I don't know if having such entry has some use.

The only solution I found for now is to skip storing flash scope objects (since fortunately I don't use flash scope) by rewriting FlowExecutionImpl and commenting out the code inside "saveFlashMessages(RequestContext)" and guarding for null in getFlashScope() in method "createMessageContext(MessageSource)" which is highly discouraged.

Here is a link to the post I wrote in the SpringMongo forum:
http://forum.springsource.org/showth...MongoConverter

I am using SpringWebflow 2.3.0.RELEASE and SpringMongo 1.0.0.RELEASE.

Thanks,
Marco

[marcovmx]

I expected to have an answer to this thread from any of the spring web flow team members, since I considered this issue to be sensitive because it makes two of the spring modules incompatible and not possible to integrate. How could (spring) mongodb could actually store a null key entry coming from a spring web flow object?

[Rossen Stoyanchev]

the reason is 'messagesMemento' contains LinkedHashMap entry containing a null key ({null=[]})

Could you provide a bit more detail on how this comes about?

[marcovmx]

Thanks for responding Rossen,

Well, I have a Spring Webflow configuration with a custom conversation manager using a custom conversation reopository to store conversations with spring mongo db.

class CustomConversation implements Conversation {
	...
	public void unlock() {
		lock.unlock();
		lockCount--;
		if (lockCount == 0) {
			if (!ended) {
				repository.saveConversation(this);
			}
			CustomConversationHolder.removeConversation(getId());
		}
	}
	...

@Repository
public class CustomConversationRepository implements ConversationRepository {
	...

	
	public void saveConversation(Conversation conversation) {
		logger.debug("Saving conversation: " + conversation);
		mongoTemplate.save(conversation);
	}
	...

I didn't do anything else in special, just storing the conversations (I did not manipulate Flow Execution objects). I get a NPE when I start the flow. Digging into the source code I realized of the symptom described above. The 'messagesMemento' object gets created all by the Spring Web Flow framework, and at some point it stores an entry in its map containing a null key, and that is not possible to be stored in mongodb.

I hope that explains better.

Thanks,
Marco

[quorak]

hey Marco,

did you find a solution? Do you mind sharing your code. I'm very curious how you implemented the Mongo Conversation Abstraction.

best
tobias