Web server is a computer where the web content is stored. Basically web server is used to host the web sites but there exists other web servers also such as gaming, storage, FTP, email etc.

An application server works with a web server to handle requests for dynamic content, such as servlets, from web applications. A web server uses a web server plug-in to establish and maintain persistent HTTP and HTTPS connections with an application server.

Ex. Apache, Microsoft’s Internet Information Services (IIS) and Nginx

Web Server Working

Web server respond to the client request in either of the following two ways:

• Sending the file to the client associated with the requested URL.
• Generating response by invoking a script and communicating with database

Key Points-

• When client sends request for a web page, the web server search for the requested page if requested page is found then it will send it to client with an HTTP response.

• If the requested web page is not found, web server will the send an HTTP response:Error 404 Not found.
• If client has requested for some other resources then the web server will contact to the application server and data store to construct the HTTP response.

Application Server-

An application server is a Java™ Virtual Machine (JVM) that runs user applications. The application server collaborates with the web server to return a dynamic, customized response to a client request. The client request can consist of servlets, JavaServer Pages (JSP) files, and enterprise beans, and their supporting classes.

An application server executes and provides user and/or other app access when utilizing the installed application’s business/functional logic.

Key required features of an application server include data redundancy, high availability, load balancing, user management, data/application security and a centralized management interface. Moreover, an application server may be connected by enterprise systems, networks or intranet and remotely accessed via the Internet.

Ex.  Jboss, Weblogic, Websphere, Glassfish, Tcat Server, Apache Geronimo