VisualVM is JDK tool based on NetBeans platform, NetBeans profiler, and a handful of plug-ins which let us profile any Java application running in JDK 6 or 7. VisualVM does not works with older JDK or any JRE either 6 or 7. Starting from JDK 6 update 7 visualVM is included in the Sun JDK distribution.
Downloading and installing latest version of visualVM is straight forward, just point to Download Page grab the zip file, extract the zip file content and you are ready to go. Follow the installation instruction (4 very easy steps) here
Now, to monitor GlassFish HTTP service we need to install a visualVM plugin that can interact with GlassFish application server through its JMX/ AMX API to gather the statistics and let us view them live in our desktop application. Run visualVM using the provided script in the bin directory, Open Tools>Plugins menu item and from the available plug-ins section select VisualVM-GlassFish and press install button to install the plug-in. Restart VisualVM and now we are ready to connect to a GlassFish instance.
Now we have two options, we can either monitor a local Glassfish instance or we can select to monitor a remote Glassfish instance. All local JVM are listed under the local node and in order to create a remote connection we need to register the host under the Remote node by right clicking on the node and adding the remote host, in my case I add 192.168.1.100. Now on the remote host we may have several JXM enabled applications running, each application on its own port. Default JMX port for GlassFish application server is 8686, therefore to add a GlassFish application server running on 192.168.1.100 we can right click on its node under the Remote node and select add JMX connection, a window will open which asks you to provide the connection information including port number and credentials. default administration credentials for GlassFish are admin/ adminadmin as username/ password.
Now that The remote GlassFish is registered the right side panel should be similar to the fillowing figure
In my case I have a remote and a local GlassFish instances, When you double click on an instance a window will open that shows all monitoring information which VisialVM can gather about the running application in different panels, something similar to the following figure
This page shows general information about the JVM which we are going to monitor and some of the plug-in specific configuration which we may need to change. Make sure that you turn the HTTP Service monitoring level and WebContainer Monitoring Level to High or LOW which will result in GlassFish gathering monitoring statistics about the HTTP Service.
Now let your application server get some hit from the clients and then switch to HTTP Service Tab in order to get a general overview of your Server HTTP Service performance. Failed, Incoming, Average connections, Keep Alive, and File Cache performance can be monitored here. Following Figure shows HTTP Service Tab
Now the funny part begins, Assuming that we have a dozen of application hosted in the same GlassFish instance we expect to be able to monitor each application separately to see how HTTP service is performing for that particular application. It is easy and do-able in no more than 3 steps. Under the GlassFish node you can see Model and under the Model you can see different web applications that you have hosted in your server, double clicking on any of those applications result in viewing the HTTP Service statistics for that particular application. For example If I double click on the admingui I will get a result page similar to the next figure.
The fun part continues further I tell you that you can monitor different servlets used in your application separately. for example I can expand the admingui node and double click on ThemeServlet to get an statistical view similar to the next figure.
All statistical information which are shown includes two major factors, processing time and error/ request count. in addition to average processing time, maximum processing time, and so on.