It’s a very common situation when an application needs some runtime customization, but it’s impossible via settings and you are too lazy to change source code, or you just cannot update your application too often. In that case you may use different script engines in order to change application behavior in runtime. Moreover, the developer doesn’t have to do changes themself. It may be the duty of administrators, analysts, etc
So, I want to describe the way of one java application, from the simplest script engine up to engines with secured sandboxes.