Java Reference
In-Depth Information
As mentioned earlier, the M-let service provides for this situation by allowing
you to expand its codebase. By using its
addURL()
methods, you can add to the
list of searchable
URL
s for classes and resources. After
URL
s are added, you can
access classes at the new locations, even in order to create MBeans. For exam-
ple, follow these steps to create the
HelloWorld
MBean again without using an
M-let file:
Make sure the agent process is stopped.
1
Restart the agent using the command from section 10.3.2.
2
Connect to the
HTML
adapter of the agent and select the
MLet
MBean.
3
Invoke the MBean's
addURL()
method with the file
URL
pointing to the
ch2.jar file. In our case, this value is file://c:/jmxbook/ch10/ch2.jar.
4
After receiving the success message, go to the Admin View of the adapter.
5
Enter the appropriate parameters to create a
HelloWorld
MBean. For the
Class Loader entry, enter the
ObjectName
value for the M-let service:
MLetAgent:name=mlet
.
6
Execute the
create
request. You should receive a success message.
7
Go back to the Agent View, and you should see the new
HelloWorld
MBean in the MBean list.
8
If you experience any errors with the MBean
create
request, be sure you typed
in the correct value for the added
URL
pointing to the ch10.jar file. You can ver-
ify the value you entered by viewing the
URLs
attribute of the
MLet
MBean.
10.4 Wrapping the M-let service to
p
rovide notifications
You should know enough about the M-let service now that you could begin
including it in your
JMX
applications to expand their codebases and increase
their usefulness. However, if you used the M-let service with any frequency, you
might notice that the service does not emit any notifications. For example, you
cannot emit a notification indicating that a remote class was loaded. If your
agent persists notifications for later analysis of the agent's activity, you will prob-
ably want to include the activity of the M-let service. Otherwise, you will be miss-
ing valuable information from the activity log of your agent.
This section builds an MBean that wraps the M-let service to provide notifica-
tions for the M-let events that could occur. Figure 10.4 illustrates this idea.
