Reuse implemented business classes in a web applications

Question

I have implemented my domain layer classes and i have used them in a java application. Now i want to use same classes in a java web application,but i don't know how can i do it? In the java application we make and run some objects in main(class and method) and use them while program is running. for example an object that hold a collection of data that will be needed for all user requests. My question is: How can i create and hold such objects and data that should be available for all users and clients.

Answer 1

Place them in the application context. I.e. in a Servlet call getServletContext().setAttribute("name", yourCollection);

Then they can be retrieved by getServletContext().getAttribute("name")

Answer 2

You could create a singleton which represents the common application logic, initialising and cleaning up the common information and objects on web-app startup and shutdown.

All servkets can use the application singleton to retrieve and store.

To initialise and cleanup on web-app startup and shutdown you can define an administrative servlet which has the load-on-startup flag set in the deployment descriptor web.xml managing the application singleton from the init() and destroy() methods.