Publish server metrics via JMX using a Byteman Helper

In this tutorial we will learn how to unleash the power of Byteman by registering an Helper class which can trace some server attributes and publish them via JMX.

If you are new to Byteman I'd suggest reading the Base Documentation and the following tutorials we have published:

So we know the basics of Byteman. We will create an Helper class which will monitor a basic WebListener:

package com.sample;

import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionListener;
import javax.servlet.http.HttpSessionEvent;

@WebListener
public class SessionCounter implements HttpSessionListener {

    private int activeSessions = 0;

    public void sessionCreated(HttpSessionEvent se) {
        activeSessions++;

    }

    public void sessionDestroyed(HttpSessionEvent se) {
        if (activeSessions > 0) {
            activeSessions--;
        }
    }

    public int getActiveSessions() {
        return activeSessions;
    }

}

Now suppose we want to publish the count of activeSession without adding any line of code to the Web application. We will code an Helper class named JMXHelper that extends the org.jboss.byteman.rule.helper.Helper class. The base Helper class is responsible for handling a Byteman Rule file, providing the base syntax of it.

In our case, we will need additional functionalities as we want to publish an MBean, with the activeSessions, via JMX. Here is our JMXHelper class:

package org.jboss.byteman.sample.helper;

import org.jboss.byteman.rule.Rule;
import org.jboss.byteman.rule.helper.Helper;

import javax.management.MBeanServer;
import javax.management.ObjectName;

import java.lang.management.ManagementFactory;

import javax.management.StandardMBean;

public class JMXHelper extends Helper {
    static Data user = new Data("activeCount", 1);
  

    private static boolean DEBUG;

    public static void activated() {
        DEBUG = Boolean.getBoolean("org.jboss.byteman.sample.helper.debug");
        if (DEBUG) {
            System.err.println("JMXHelper  activated");
        }
    }

    public static void installed(Rule rule) {
        if (DEBUG) {
            System.err.println("JMXHelper installed, " + rule);
        }
    }

    protected JMXHelper(Rule rule) {
        super(rule);

    }

    public void registerHelperMBean(String name) {
        MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
        synchronized (this) {

            try {
                ObjectName oname = new ObjectName(name);

                if (mbs.isRegistered(oname) == false) {

                    StandardMBean mbean = new StandardMBean(user, DataMBean.class);

                    mbs.registerMBean(mbean, oname);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public void traceToJMX(int active) {

        user.setValue(active);
        System.out.println("Number of Active Sessions: " + active);
    }

}

The method which is responsible for registering the MBean is registerHelperMBean which requires to be invoked at Server start. The other method is traceToJMX which merely sets the MBean attribute which will be passed from our Rule. Within the Helper class we referenced a Java Bean named DataMBean which is an ordinary Java Bean, fit to be used as StandardMBean:

package org.jboss.byteman.sample.helper;

 public interface DataMBean {
       
    public int getValue();
    
    public void setValue(int value);

    public String getAttribute();

    public void setAttribute(String attribute);
}

Now we will code our rule file- we will name it session.btm:

RULE Register Helper mbean
CLASS org.jboss.modules.Main
METHOD main
HELPER org.jboss.byteman.sample.helper.JMXHelper
AT EXIT
IF TRUE
DO registerHelperMBean("org.jboss.byteman:helper=JMXHelper")
ENDRULE


RULE Count Active Sessions
CLASS com.sample.SessionCounter
HELPER org.jboss.byteman.sample.helper.JMXHelper

METHOD sessionCreated(HttpSessionEvent)
AT EXIT

BIND count:int = $0.getActiveSessions();

IF true
DO traceln("Session count "+count);
traceToJMX(count);
 

ENDRULE

The first rule is used to register our MBean class through the JMXHelper. It fires when the application server starts.

The second rule is activated when the method sessionCreated of the SessionCounter class exits. At this point the number of activeSession is stored in the Rule variable named count and passed to the JMXHelper which will eventually update the MBean.

In order to run this Rule, you have to provide to the JAVA_OPTS the path to the Rule file and to the Helper class, which was packaged in a JAR file named Helper.jar and placed in /home/jboss/dist/ .

JAVA_OPTS="$JAVA_OPTS -Dorg.jboss.byteman.transform.all -javaagent:/home/jboss/byteman-download-3.0.3/lib/byteman.jar=script:/home/jboss/byteman-download-3.0.3/sample/scripts/session.btm,boot:/home/jboss/dist/ByteHelper.jar,boot:/home/jboss/byteman-download-3.0.3/lib/byteman.jar"

Update the above shell with the path to your files. Now start the application server and deploy the Web application which contains the SessionCounter class. You should be able to see on the Console, as soon as you invoke some JSP files:

INFO  [stdout] (default task-49) Number of Active HTTP Sessions: 2

Troubleshooting Byteman

Hint: If you are experiencing issues in firing your rules, include as well the -Dorg.jboss.byteman.verbose in the JAVA_OPTS 

Now open JConsole (or any other tool which is able to inspect the MBeans on the application server) and verify that the attribute is correctly updated in the MBean tree: 

Byteman helper tutorial

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