can we write main() in jsp

how can we write main() in JSP?then how it will execute?

Yes, but why in the world would you want to do this?
You can put a main method in a jsp just like you can put any other method. The purpose of it eludes me, however. Especially since scriptlets are bad practice.

A JSP is just a kind of servlet, you know. A servlet is a java class. You can put a main method in at will. There's just no point to it.

You could not use a main() method for any kind of testing because a JSP depends on executing in the servlet container environment with a request and response , etc etc objects created by that environment.

Testing outside the servlet environment can be very helpful but you need to write classes that don't depend on the container.

Bill