How can I run a piece of Script inside an already running Java Process

Question

Today, I was using AdaptJ Stacktrace tool. I am wondered how can it run a BeanShell script inside an already running process! The process is not run in debug mode. Even, the JVM is run with attach mechanism disabled! After all, the class path does not contain the BeanShell jar files. But you can easily select a running java process, open a BeanShell console and run whatever command you want inside the running process.