java - Try to use Agent in Webapplication for bytecode Manupulation -

i'm not in java have webapplication running on wildfly. have 3 threads call function insert logs in in , function saves logs database , after every thread sends time how long did takes this. send data programm wrote has 3 threads call 1 of 3 server threads.

so try bytecode manipulation every thread on server saves datetime call log function waits 1 second , returns time needed.

1 thread write in logfile before or after waitet 1 second. part wait second , call log function want inject every 3 threads bytecode manipulation.

public class mytransformer implements classfiletransformer {   @override public byte[] transform(classloader loader, string classname, class redefiningclass, protectiondomain protectiondomain, byte[] bytes) throws illegalclassformatexception {      return transformclass(redefiningclass, bytes); }  private byte[] transformclass(class classtotransform, byte[] b) {     classpool pool = classpool.getdefault();     ctclass cl = null;     try {         cl = pool.get("de.soptim.ws.myapplication");     } catch (javassist.notfoundexception e) {         e.printstacktrace();     }     try {          assert cl != null;         ctmethod[] methods = cl.getmethods();         (int = 0; < methods.length; i++) {             if (methods[i].isempty() == false) {                 changemethod(methods[i]);             }         }         b = cl.tobytecode();     } catch (exception e) {         e.printstacktrace();     } {         if (cl != null) {             cl.detach();         }     }     return b; }  private void changemethod(ctmethod method) throws notfoundexception, cannotcompileexception {      if (method.hasannotation(loggable.class)) {         method.insertbefore("threadlogger.info(\"added bytecode !!!\");");         method.insertafter("threadlogger.info(\"added bytecode !!!\");");     } }} 

thats transformer class should increase code methods need checks method has @loggable annotation adds code it("at moment it's log statments checking if works")

my biggest problem don't know how call agent ... googled hwo call agent @ runtime agentmain() think dind't understood how works.

agent class

public class logagent  {  public static void agentmain(string agentargs, instrumentation inst) {     system.out.println("starting agent");     inst.addtransformer(new mytransformer()); }} 

hope understand problem :) , if answere pleas try stay noob friendly :d.

you don't call agent explicitly, should specify additional argument jvm :

java -javaagent:jarpath[=options]

where jarpath path jar containing agent. jvm invoke premain method before main method of java program.

and transform method called before classloading jvm (you don't call explicitly).

last remark : should implement premain method, not agentmain. agentmain used during attaching running vm, while premain used when start jvm -javaagent method.

and make sure jar have valid manifest, described : https://docs.oracle.com/javase/8/docs/api/java/lang/instrument/package-summary.html

i haven't using javaassit cannot code valid, instrumenting webapp server wildfly harder normal java app (mostly due classloaders visibility , hierarchy).

see :

http://www.tomsquest.com/blog/2014/01/intro-java-agent-and-bytecode-manipulation/ tutorials javaagents