jconsole

​Some good resources/tutorials:
https://www.youtube.com/watch?v=iixQAYnBnJw
​https://www.toptal.com/java/hunting-memory-leaks-in-java

I'm not going to talk too much about what it is, it's all here:                                               
​ ​https://docs.oracle.com/javase/1.5.0/docs/guide/management/jconsole.html

This post is primarily to learn how to use it.

Start off with a Java program that runs indefinitely and creates objects.

import java.time.Instant;

class Jmap{
                String name;
                
                public Jmap(String name) {
                        this.name = name;
                        System.out.println("New Object with name " + name + " created");
                }
                
                @Override
                public void finalize() {
                        System.out.println("Obkect with name " + name + " destroyed");
                }
                
                @Override
                public String toString() {
                        return this.name;
                }
        }


public class JMapTutorial {
        

        public static void main(String[] args) {
                Jmap j;
                while(true) {
                        try {
                                Thread.sleep(10000);
                                j = new Jmap(Instant.now().toString());
                        } catch (InterruptedException e) {
                                
                                //e.printStackTrace();
                        }
                }
        }

}

​Find the Java process running using command:

ps -ef | grep java

look for what you want to monitor, in this case I had (the PID I need is in red):

501 90817   555   0 12:31PM ??         0:00.33 /Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/bin/java -Dfile.encoding=UTF-8 -classpath /Users/gulanurmatova/eclipse-workspace/bin JMapTutorial


Run the JCONSOLE:

$ jconsole 90817

Output of the program  run below and the screenshot of the Jconsole - everything makes sense so far - create, create, create, bunch of clean-ups and then again create, create, create. Let's see what happens next...