8.2. Nested conversations

A nested conversation is created by invoking a method marked @Begin(nested=true) within the scope of an existing conversation. A nested conversation has its own conversation context, but can read values from the outer conversation's context. The outer conversation's context is read-only within a nested conversation, but because objects are obtained by reference, changes to the objects themselves will be reflected in the outer context.

When an @End is subsequently encountered, the nested conversation will be destroyed, and the outer conversation will resume, popping the conversation stack. Conversations may be nested to any arbitrary depth.

Certain user activities (workspace management, or the back button) can cause the outer conversation to be resumed before the inner conversation ends. In this case, it is possible to have multiple concurrent nested conversations belonging to the same outer conversation. If the outer conversation ends before a nested conversation ends, Seam destroys all nested conversation contexts along with the outer context.

The conversation at the bottom of the conversation stack is the root conversation. Destroying this conversation will always destroy all descendant conversations. You can achieve this declaratively by specifying @End(root=true).

A conversation can be thought of as a continuable state. Nested conversations allow the application to capture a consistent continuable state at various points in a user interaction, thus ensuring truly correct behavior in the face of backbuttoning and workspace management.

As mentioned previously, if a component exists in a parent conversation of the current nested conversation, the nested conversation will use the same instance. Occasionally, it is useful to have a different instance in each nested conversation, so that the component instance that of the parent conversation is invisible to its child conversations. You can achieve this behavior by annotating the component @PerNestedConversation.