How can I add a Javaagent to a JVM without stopping the JVM?

Question

I wish to profile a Java application without stopping the application. Can I add a Javaagent somehow while the application is running?

Answer 1

See Starting a Java agent after program start.

It links to http://dhruba.name/2010/02/07/creation-dynamic-loading-and-instrumentation-with-javaagents/ that under "Dynamic loading of a javaagent at runtime" provides working example:

public static void loadAgent() throws Exception {     String nameOfRunningVM = ManagementFactory.getRuntimeMXBean().getName();     String pid = nameOfRunningVM.substring(0, nameOfRunningVM.indexOf('@'));     VirtualMachine vm = VirtualMachine.attach(pid);     vm.loadAgent(jarFilePath, "");     vm.detach(); } 

Note that Java 9 requires -Djdk.attach.allowAttachSelf=true to be present among JVM startup arguments.

Answer 2

You can use ea-agent-loader

With it loading an agent in runtime will look like:

public class HelloAgentWorld {     public static class HelloAgent     {         public static void agentmain(String agentArgs, Instrumentation inst)         {             System.out.println(agentArgs);             System.out.println("Hi from the agent!");             System.out.println("I've got instrumentation!: " + inst);         }     }      public static void main(String[] args)     {         AgentLoader.loadAgentClass(HelloAgent.class.getName(), "Hello!");     } }