Thursday, August 30, 2007

Seam Error Messages

I've been reading JBoss Seam : Power and Simplicity Beyond Java EE (Amazon link) and working through the examples from Michael Yuan's site.

After playing with the example from Chapter 6 : A Simple Stateful Application, I decided to change the ManagerAction class from a session scoped variable to a conversation scoped variable.

I changed "@Scope(SESSION)" to "@Scope(CONVERSATION)", added a "@Begin" to the "sayHello()" method, and added "@End" to the "startOver()" method and redeployed.

I had breakpoints set inside the sayHello and startOver methods and was debugging in Eclipse Europa.  I wanted to watch the memory addresses of the ManagerAction over multiple submits to verify that different browser tabs would spawn different conversations.

The change didn't work.  I got,

14:22:29,544 FATAL [application] javax.ejb.EJBException: java.lang.IllegalStateException: begin method invoked from a long running conversation, try using @Begin(join=true) on method: sayHello

I decided to follow the error message's advice.  It worked -- nice error message!

I started two conversations in two browser tabs, the urls displayed differenct conversation ids, and Eclipse showed different memory addresses when I hit the breakpoints.  However, when I entered different one word names, "Bill" and "Mickey" (I was listening to DeadPod) and tried different responses to the prompt, I encountered a problem.  When I would choose the "Oops, let me go back and change" option the name would be the same in both windows.

I checked the Person object, and it was session scoped.  I removed the @Scope annotation and everything worked as expected.

Hibernate often throw nice error messages, and I'm glad to see that has been carried over to Seam.  Nice work!

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