update on my own issue.
I made it work with AOP precompilation instead of using javaagent.
of course, I had to get over some hurdles of the jar library issue in oc4j.
The above error means you are missing javassist.jar from the agent classpath, or some other jar it requires
i knew the missing class it was complaining about is in javassist.jar file, and I made sure all the jars are in the classpath, that was the basic step everyone would do.
finally, i opened oc4j.jar of oc4j, i noticed it used some special way of load all the library jar in the boot xml.
anyway, AOP precompilation worked like a charm.