Using JConsole to connect to an MBeanServer (JMX agent)

Here's some insights and tips on accessing the JMX Agent using JConsole.

JConsole is the most handy way to connect and test your JMX services since it comes with every JDK from Java 5 onwards. If you have your jdk/bin directory included in your path, it's just a matter of running it from a command prompt by typing:
jconsole

Its usage is pretty straightforward too. Once it's loaded, you can choose to connect from one of 3 options: Local, Remote and Advanced - there's one tab for each of these.

1. Local - If you had registered your MBeans with the default JVM's MBean Server, select the Local tab. Here, the MBeans will be automatically displayed and all that needs to be done is to click on Connect.
2. Remote - I find Advanced is actually simpler than this tab - so skipping this...
3. Advanced - If you had registered your MBean from an application that you deployed on a J2EE server (like Sun One), then there are a few more steps as you have to use the Advanced tab.
• Obtain your JMX connection URL either from the admin console or the server.log (it appears right after the server start-up entry - something like service:jmx:rmi:///jndi/rmi://localhost:8686/management/rmi-jmx-connector).
• Type this into the JMX URL field.
• Enter your server's username and password into those respective fields as well and click connect.

That's it! You're connected. You'll see a whole array of information - there's a chance you'd get overloaded! Head on over directly to the MBeans tab - here you can view all the MBeans successfully registered on this MBeanServer, in the Tree view on the left. Again, don't worry if you can't find yours at first - there might be lots of internal MBeans that the server registers that are crowding the list. Your MBean should appear in its fully qualified form, i.e. <<packagename>>.<<classname>>. Its pretty straightforward from here on - you can easily find your exposed methods / attributes and invoke / change them too.

Ok, seemed pretty easy but in real life, you would most probably run intos ome hiccups even before connecting. Most are obvious enough from the error messages. But what if you needed more details than one-line messags to troubleshoot? Unfortunately, the default Jconsole messages are not very helpful.

This is where you have to override the default values to get full stacktraces and much more.
This is a simple 2 step process:

1. First download my sample log configuration file here.
2. To enable detail messages, start jconsole with an extra argument:
   jconsole.exe -J-Djava.util.logging.config.file=<<properties>>
   where <<properties>> is the name of the downloaded log configuration file.

And you're done. You should get a detailed breakdown of the steps in between and full stacktrace of any errors in the command prompt window from which you launched JConsole.

Using JMX

JMX is an integral part of J2EE but mostly neglected compared to other aspects. Here's some practical learnings.

Understanding
JMX is used to manage your application (or even the application server). It's a very simple 3-step process.

1. You write your Management Beans or MBeans to provide the management functionality.
2. Then your register your MBean with the MBean Agent (MBean Server).
3. Now you can manage your application by connecting to the MBean Server and calling the required functionality.

When to use
The decision of when to forgo the use of configuration files and code to update settings and when to use JMX is not clear-cut. It's definitely a better idea when program management forms a larger part since JMX is very scalable. But I think JMX is an even better idea when you have limited managment requirements and don't want to add a custom user interface module just for the management. In this case, JMX allows you to provide the neccessary interface with just 10 lines of code and use of the ubiquitous JConsole to do the agent connection (see my Using JConsole to connect to an MBeanServer post on how to use JConsole for this).