Java Reference
In-Depth Information
D
At some point, an
EJB
client will complete this workflow or abort it and must
remove the
EJB
from existence. It does so by calling the
ejbRemove()
method. This
method does two things. First, it invokes the
removeEJBMBean()
method, which
unregisters the MBean that was exposing the
EJB
for management. This way, even
if the remaining operations of this method fail, the MBean will not exist. The sec-
ond task for
ejbRemove()
is to delete its persistent state from the database.
These next few methods are the reason you wrote this Enterprise JavaBean. The
installEJBMBean()
EJB
method creates and initializes a
WorkflowManager
MBean
to expose the remote interface methods from this
EJB
. To do this, the
EJB
must
create an instance of the MBean. It does so by calling the constructor that takes
two arguments: a
String
value acting as the
clientid
value that initialized the
EJB
, and a
String
value that represents the
JNDI
name used to look up the home
interface of this
EJB
. Once the
WorkflowManager
MBean looks up the home inter-
face, it can use the
clientid
value to find the appropriate
WorkflowBean
EJB
to
expose for management.
After creating a
WorkflowManager
MBean instance, the
EJB
must register it on
a MBean server. How to acquire an MBean server depends on the application
server containing your application. To encapsulate the MBean server discovery,
the
EJB
provides a
getMBeanServer()
method, which stubs out the code necessary
to acquire the MBean server.
After acquiring an
MBeanServer
instance, the
EJB
must register its new
Work-
flowManager
MBean. Recall that the
ObjectName
class is a
JMX
class that acts as a
key on the MBean server to a particular MBean instance. It contains a domain
name and a property list that makes it unique across the
MBeanServer
instance. To
create an instance of the
ObjectName
class, you use the constructor that accepts a
domain name and a single key and value argument. Now that you have an MBean
instance, an
MBeanServer
instance, and an
ObjectName
instance, you can register
the MBean by invoking the MBean server's
registerMBean()
method.
The
ejbRemove()
method invokes the
removeEJBMBean()
method before it deletes
its state from the database. The
removeEJBMBean()
method looks up an instance of
the
MBeanServer
(just like the install method) by invoking the
getMBeanServer()
method. It also creates an instance of
ObjectName
that represents the
EJB
's MBean,
and calls the
unregisterMBean()
method to remove it.
E
F
14.5.2
Constructing the WorkflowManager MBean
Let's recap what you have accomplished. You have created an entity bean that rep-
resents a client's state as it moves through a business workflow. The
Workflow
EJB
,
