JMX and Jolokia

Reference: okminseok.blogspot.com, github.com/eugenp

What is JMX?

• A technology that defines a complete architecture and a set of design patterns for monitoring and managing Java Applications

• Think of it as an API that allows you to monitor the state of a running application and change its settings

  • It enables managing applications at runtime

  • It has been included as a standard feature since JDK 1.5

    • It was originally created to provide various features for application management

JMX Terminology

• ManagedResource

  • A resource that is the target of management

• MBean (Managed Bean)

  • A class instantiated in the JVM through dependency injection to represent a resource

  • Provides monitoring and management capabilities for Java applications

  • Provides an interface for accessing and manipulating ManagedResources

• MBean Server

  • A Java Class that manages MBeans

  • MBeans are registered with the MBean server, and the MBean server manages all remote managers that access resources

  • An element that acts as a mediator between MBeans, applications in the same JVM, and external systems

  • All interactions with MBeans are done through the MBean Server

• Management Application

  • An application that manages applications built using JMX

• Notification

  • A Java object that wraps events, alerts, and information generated by MBeans

• Instrumentation

  • Resources managed by MBeans

Getting Started with JMX

• To manage resources through JMX, you need to create Managed Beans called MBeans, and

  • Register the created MBeans with the MBean Server

    • The MBean Server acts as an agent that manages registered MBeans

    • The MBean server is launched internally within the implemented application

• There are rules for implementing MBeans:

  1. You must create a pair of interface and implementation,

  2. The name of the MBean interface must end with "MBean"

• If you only want to monitor exposed variables, you can omit the setter

ex)

import java.lang.management.ManagementFactory;

public interface MonitoringBean {
    long getStorageSize();
}

public class Monitoring implements MonitoringBean {
    @Override
    public long getStorageCount() {
        return ...;
    }
}

// boot up MBean server
Monitoring monitoring = new Monitoring();

// Create an MBeanServer instance from the ManagementFactory class
MBeanServer server = ManagementFactory.getPlatformMBeanServer();

ObjectName jmxObjectName = new ObjectName("com.chloe.example:type=basic,name=monitor");
server.registerMBean(monitoring, jmxObjectName);

• ObjectName has a structure of domain and key

  • By convention, the domain uses the Java package name to avoid naming conflicts

  • Keys can have multiple key=value pairs separated by commas

Jolokia and JMX

• Generally, only Java code can directly access the JMX API, but there are adaptors that convert the JMX API to standard protocols

  • One of them is Jolokia, which converts the JMX API to HTTP

• Jolokia is an agent that can be deployed in a JVM,

  • It exposes MBeans through REST-like HTTP endpoints,

  • Making all information easily available to non-Java applications running on the same host

    • In a standard JVM, it can be deployed as an agent,

    • In Java EE, it can be deployed as a WAR, OSGI, or Module agent