How to load JavaAgent and run method from it?

Question

I'm new in JavaAgent concept, so maybe this issue isn't complicated. But I hope some discussion and knowledge arrangement will be helpful (not only for me).

So - what I want to do? I would like to load external jar library when I start my application. This external library is under development and versioned on ARM (Nexus) and contains functionalities which are essential in my_app.

My attempt:

1. Download wanted version of lib (no problem here - got proper func_version.jar in right place)

2. I add in parent dir of downloaded jar class JavaAgent.java:

   import java.lang.instrument.*;
   
   public class JavaAgent {  
       private static Instrumentation inst;  
   
       public static Instrumentation getInstrumentation() { return inst; }  
   
       public static void premain(String agentArgs, Instrumentation inst) {  
           System.out.println(inst.getClass() + ": " + inst);  
           System.out.println("JavaAgent LOADED!");
           JavaAgent.inst = inst;  
       }  
   }  
   

3. Modify META-INF/MANIFEST.MF in lib (added line: Premain-Class: JavaAgent)

4. Try to load JavaAgent by passing it as JVM parameter:

   java -javaagent:/home/func_1.0.1.jar /home/my_app/MyStartup
   

MyStartup.java contains main method for my_app.

I know this steps are not enough (can't see any result yet). But is it a right approach? And what else do I need to do to see wanted "JavaAgent LOADED!" on console output? Some work with Java ClassLoader is needed?