I am trying to instrument a jar file (main.jar) with javaagent.jar using BCEL. basically where ever I find any aload in bytecode, I m trying to insert a function call to a static function called Fun() in class "someclass" using

// this code is in BCEL same can be written using javaassist 

if (opcode instanceof aload) { iFactory.createInvoke("someclass", "fun", Type.VOID, new Type[]{}, Constants.INVOKESTATIC); 

my "someclass" class reside in javaagent.jar

on executing

java  -javaagent:javaagent.jar -jar main.jar

or

java  -javaagent:javaagent.jar -jar main.jar javaagent.jar

or (I created a separate jar for my "someclass" called someclasscontained.jar)

java   -javaagent:javaagent.jar -cp "someclasscontained.jar;main.jar "

I am getting

Exception in thread "main" java.lang.NoClassDefFoundError: someclass

error. i tried with -bootclasspath/p option but still not working. does anyone has any clue?

(1) all jar resides in same folder 2) used fully qualified class name 3) checked silly mistakes