jboss seam and jbpm async nodes

In a jboss seam project i wanted to use async nodes in a jbpm workflow. You can add "async=true" to any node in you jbpm process definition. This makes the workflow continue in the background so your user interface does not have to wait for the complete workflow to complete.

I accomplished this by starting the JbpmThreadServlet by adding in the web.xml:

 <!-- Jpbpm Thread listener which will do async continuations & Timer -->

 <servlet>
     <servlet-name>JbpmThreadsServlet</servlet-name>
     <servlet-class>org.jbpm.web.JbpmThreadsServlet</servlet-class>
     <load-on-startup>1</load-on-startup>
 </servlet>
 <servlet-mapping>
     <servlet-name>JbpmThreadsServlet</servlet-name>
     <url-pattern>/jbpmthreads</url-pattern>
 </servlet-mapping>

When your web application starts, jbpm will spawn off a thread that will continue your workflow. This thread is also being used for sending out email notifications of task nodes.

A problem that rises here is that your action handlers don't have access to the seam contexts. To solve this problem I made a abstract action handler which will startup the seam lifecycle from a such an actionHandler if it does not exist. This code comes from the seam 2.0.0 framework which actually support this. I haven't tried it out still.

The code for the actionHandler is:

import org.jboss.seam.contexts.Contexts;
import org.jboss.seam.contexts.Lifecycle;
import org.jboss.seam.core.BusinessProcess;
import org.jbpm.graph.def.ActionHandler;
import org.jbpm.graph.exe.ExecutionContext;
import org.jbpm.taskmgmt.exe.TaskInstance;

public abstract class SeamContextualActionHandler implements ActionHandler {

        abstract public void executeInSeam(ExecutionContext context)
                        throws Exception;

        public void execute(final ExecutionContext context) throws Exception {

                try {
                        if (Contexts.isEventContextActive()
                                        || Contexts.isApplicationContextActive()) //not sure about the second bit (only needed at init time!)
                        {

                        } else {
                                Lifecycle.beginCall();
                                try {
                                        initProcessAndTask(context);
                                        executeInSeam(context);
                                } finally {
                                        Lifecycle.endCall();
                                }
                        }
                } catch (RuntimeException re) {
                        throw re;
                } catch (Exception e) {
                        throw new RuntimeException(e);
                }
        }

        private static void initProcessAndTask(ExecutionContext context) {
                BusinessProcess businessProcess = BusinessProcess.instance();
                businessProcess.setProcessId(context.getProcessInstance().getId());
                TaskInstance taskInstance = context.getTaskInstance();
                if (taskInstance != null) {
                        businessProcess.setTaskId(taskInstance.getId());
                }
        }

}

Your actionHandlers should extend this class and implement the executeInSeam() method instead of the execute method from the ActionHandler interface.