InjectAgent.java

import com.sun.tools.attach.VirtualMachine;

import java.nio.file.Paths;

public class InjectAgent {

    public static void main(String[] args) throws Exception {
        String PID = args[0];
        String agentJar = Paths.get("retransformer.jar").toAbsolutePath().toString();

        VirtualMachine vm = VirtualMachine.attach(PID);
        try {
            vm.loadAgent(agentJar);
        } finally {
            vm.detach();
        }
    }
}