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Understanding Seam Nested Conversations and Timeouts

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State management has always been a challenge for web application developers. Handling interactions at an application level instead of a request level is what conversations manage. Jacob Orshalick discusses Seam's conversation model with an explanation of how nested conversations work with Seam's demo booking example, a hotel booking application.

Seam's conversation model provides a simplified approach to continuations. If you are familiar with the concept of a continuation server you are aware of the capabilities they provide including seamless back-buttoning and automatic state management. A user session has many continuations that are simply snapshots of state during execution and the continuations can be reverted to at any time. If you are not familiar with this concept, not to worry, Seam makes it simple.

This is just part of the model, Seam also allows the conversation nesting:

Nesting a conversation provides a state container that is stacked on the state container of the original or outer conversation. Any objects that are set into the nested conversation's state container do not affect the objects accessible in the parent conversation's state container. This allows each nested conversation to maintain its own unique state.

Orshalick goes through the ways to define a nested conversation as well as make sure it has properly cleaned up. An example of extending the Seam booking example using JBoss Developer Studio concludes a descriptive example of nested conversations.

Nested conversations isn't the only thing that Jacob Orshalick has been clearing the air about with Seam, he has also discussed the topic of conversation timeouts:

Conversation timeout seems to be a commonly misunderstood Seam concept. I often see postings on the Seam forums claiming that the conversation-timeout doesn't work! Well, actually it does, you simply have to understand the semantics.

Using same examples as with nested conversations, Orshalick shows that when dealing with multiple conversations only the background conversation is affected by the conversation timeout. With this being said, the foreground conversation would timeout when the session itself times out.

Orshalick's concluding thoughts:

Seam offers a very attractive approach to state management through its simple conversation model. Complicated issues developers struggled with in the past including multi-window operation and back-buttoning are handled seamlessly.

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