DAO pattern - where do transactions fit in?

Question

So I\'ve got this generic DAO thing going on and at face value it appears to be ok. It\'s basically modeled after the CaveatEmptor sample application from the Hibernate guys.

Answer 1

In a web app, what I do to demarcate transactions is to take advantage of the HTTP request/response cycle, where each atomic business operation executes in the scope of one of these cycles, in a single dedicated thread.

Whatever web framework is used (Struts, JSF, GWT, etc.), there typically exists a "seam" where transaction demarcation can be performed. In Struts, it can be a base Action class. In GWT, it can be a base RemoteServiceImpl class.

So, use that central point of access to open the transaction (before allowing the application-specific code to execute), and to terminate it with a commit if no exceptions bubbled up or a rollback otherwise (after the application-specific code was executed).

I applied this strategy extensively in a large and complex business web app, and it proved to work very well.