How to create a `javaagent` executable jar

ExampleAgent.java

import java.lang.instrument.Instrumentation;

/**
 * Let's say you have an existing application that is an executable jar file (e.g. app.jar)
 * Define this class a directory of your choosing.
 * Then create the following manifest.txt file:
 *  <code> $ echo "Premain-Class: ExampleAgent" > manifest.txt</code>
 * Then create the jar file for this class:
 *  <code> $ jar cmf manifest.txt example-agent.jar *.class</code>
 * Lastly, start your existing app.jar like so:
 *  <code> $ java -javaagent:/full/path/to/example-agent.jar -jar app.jar</code>
 */
class ExampleAgent {
  public static void premain(String args, Instrumentation inst) {
    System.out.println("################################ in premain");
  }
}