Yes you can do that:

Boolean started = (Boolean) getServer().getAttribute(new ObjectName("jboss.system:type=Server"), "Started");

As soon as JBoss has completely finished start up "started" is true.

The implementation of getServer() depends on how you want to access the server: within an MBean, any class within the VM JBoss runs or remote. For example if you want to get a reference remotely via RMI:

InitialContext context = new InitialContext(properties);
Object o = context.lookup("jmx/invoker/RMIAdaptor);
RemoteMBeanServer mbeanServer = new RMIConnectorImpl((RMIAdaptor) o);

Thorsten