ServletContext is a interface which helps us to communicate with the servlet container. There is only one ServletContext for the entire web application and the components of the web application can share it. The information in the ServletContext will be common to all the components. Remember that each servlet will have its own ServletConfig. The ServetContext is created by the container when the web application is deployed and after that only the context is available to each servlet in the web application.
Web application initialization:
The Context init parameters are available to the entire web application not just to the single servlet like servlet init parameters.
How can we do the mapping of the Context init parameters in web.xml
In the servlet code we will write this as
ServletContext context = getServletContext();
Recommend the tutorial