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1. Introduction

• JMX - Java Management extensions
  • export standard metrics and custom metrics using MBeans to a monitoring system
  • understand how your application is performing
    • memory
    • cpu
    • threads
    • API calls in a REST endpoint

2. Why need this?

• Large scale java applications
  • gather performance information
    • number of users connected
• could provide a monitoring interface
• any class that exports data to JMX is called a Managed Bean(MBean). These MBeans publish their metrics to a MBean Server provided by the Java platform.

3. Components

3.1 MBean

• Objects with methods that return information and export the information via the MBeanServer
• Mainly have 4 types
  • Standard MBean
    • create an interface with getter
  • Dynamic MBean
    • implements getters and setters to retrieve or modify the metric that can be auto discovered by implementing the javax.management.DynamicMBean interface
  • Model MBean
    • Generic, dynamic in runtime to instrument the resources
  • Open MBean
    • Using a predefined set of java classes

4. Example

// Create an interface that the MBeanServer will retrieve information 
public interface SystemStatusMBean {
   Integer getNumberOfSecondsRunning();
   String getProgramName();
   Long getNumberOfUnixSecondsRunning();
   Boolean getSwitchStatus();
}

Actual Implementation

    public class SystemStatus implements SystemStatusMBean {
   private Integer numberOfSecondsRunning;
   private String programName;
   private Long numberOfUnixSecondsRunning;
   private Boolean switchStatus;
   private Thread backgroundThread;

   public SystemStatus(String programName) {
       // First we initialize all the metrics
       this.backgroundThread = new Thread();
       this.programName = programName;
       this.numberOfSecondsRunning = 0;
       this.numberOfUnixSecondsRunning = System.currentTimeMillis() / 1000L;
       this.switchStatus = false;

       // We will use a background thread to update the metrics
       this.backgroundThread = new Thread(() -> {
           try {
               while (true) {
                   // Every second we update the metrics
                   numberOfSecondsRunning += 1;
                   numberOfUnixSecondsRunning += 1;
                   switchStatus = !switchStatus;
                   Thread.sleep(1000L);
               }
           } catch (Exception e) {
               e.printStackTrace();
           }
       });
       this.backgroundThread.setName("backgroundThread");
       this.backgroundThread.start();
   }

5. Operations and attributes

Class properties exported through MBeans are called attributes, and methods exported through MBeans are called operations.

• TotalCompilationTime
  • Total time spent doing in JIT compilation
• Garbage Collector - CollectionCount
  • Number of garbage collection events fired since the JVM launch
• Garbage Collector - CollectionTime
• FreePyhsicalMemorySize
• CommitedVirtualMemorySize
  • The amount of memory that is guaranteed to be available for use by JVM
• ProcessCpuTime
  • Time CPU has spent running the process
• PeakThreadCount
  • maximum number of threads being executed at the same time since the JVM was started or the peak was reset
• ThreadCount
  • the number of threads running at the current moment

Reference

1. https://sysdig.com/blog/jmx-monitoring-custom-metrics/

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