The primary role of the application server is to take care of the business logic. Java applications servers also enable deployment and execution of servlets, the compilation of Java server pages, access to databases and the management of the users' state. Application servers can be loaded on any machine. Often, one or more servers are set up for deployment.
Journal of Object Technology
Lyon, Douglas A., "Creating Servlets with Intellij V8" (2009). Engineering Faculty Publications. 66.
Douglas Lyon, “Creating Servlets with Intellij V8”, Journal of Object Technology, Volume 8, no. 2 (March 2009), pp. 15-28