JavaCard OS

I have to write a simple JCVM in C language,but I am experiencing a problem. Such as method invoke,if I invoke a method in a package,the byte-code is in the cap file. But if it is in JavaCard API like apdu.getbuffer(),how can I implement it? I just need to implement a simple version of JavaCard API, please help.

1. Change your applet build process to intercept the generated classes before JAVA CARD bytecode conversion, and make a jar;
2. Dynamically load this jar in a driver program;
3. Using reflection , call the entry point "install()" in the loaded class - this will call the applet constructor and try to call back register() - you will have to implement this API and others.

Thank you for your help. Now I am confused about a basic question.
Does the java card API stored in a card in cap file form?

It is up to your implementation.