I didnt know much about CtMethod.instrument() and ExprEditor and its edit methods before. You can use them to solve the above problem:

// Suppose you want to know from where the insertBefore code of 'myCtMethod' is running, You can add a boolean 
// field to the class for this purpose. unfortunately, we need a FIELD for every 'instrumented' method because Javassist DOES NOT ALLOW access to LOCAL VARIABLES 
// including those added using its own addLocalVariable() method. In our case, I call 
// the boolean field as 'inHandler'. Set it to false upon initialization.
  
   myCtMethod.instrument(new ExprEditor() {
   public void edit(Handler myHandler) throws CannotCompileException {
    try {
   
     // insertBefore inserts the statement before the catch block is entered. You can even change the exception here, i think.
     // Here I set inHandler to true signifying entry into the catch block.
     myHandler.insertBefore("inHandler = true;");  // inHandler is an (added) field of the CtClass containing myCtMethod
     
     // Below statement prints some description of the handler object, if needed.
     myHandler.insertBefore("System.out.println(\"Instrumentation detected presence of a Handler for " + myHandler.getType().getName() + " at line number " + myHandler.getLineNumber()+"\");");
    } catch (NotFoundException ntfnde) {
     ntfnde.printStackTrace();
    }
   }
  });


// The below if statement will distinguish between normal code and exception handler code and execute accordingly
  sayCtM.insertAfter("if (inHandler == true) System.out.println(\"Running within a handler.\"); else System.out.println(\"Running in normal code\");");

Message was edited by: Arvind K