Steve's 101 pcs of info.: Web / application server

Web server refers to a computer or program that responds HTTP requests from a client (browser e.g. IE or Firefox). The HTTP response usually consists of HTML document (i.e. web page) and other raw file such as image. A commercial web server should include other features like HTTPS (allowing encrypted connection), logging, authentication / authorization etc. Wikipedia gives a comparison of web server software.

Application server is distinguished from web servers by the extensive use of server-side dynamic content & frequent integration with database engines. It handles the business logic & data access fo the application. The term refers to web-based applications such as e-commerce & content management system.

One particular and prominent example is the Sun Microsystems J2EE platform. J2EE includes Enterprise JavaBean (EJB) that implements business logic, Servlet for the request-response model, JavaServer Page (JSP) that puts servlet code into a text-based document, as well as Java Message Service (JMS) / Java Transaction (JTA) / JavaMail / Java Naming & Directory Interface (JNDI) etc. APIs. The Sun Java System Application Server Platform Edition 8 is a fully compliant implementation of the J2EE 1.4 platform. It includes two technologies -- JSP Standard Tag Library (JSTL) and JavaServer Faces -- and a list of tools, e.g. admin console & asadmin, a command-line AS admin utility.

Other well-known Java enterprise edition application servers are Tomcat (Apache), JBoss (Red Hat), WebLogic (BEA) etc. See also a wider list of application servers at Wikipedia, including non-Java based products e.g. .NET framework (Microsoft).

Started off as a servlet reference implementation by a software architect at Sun Microsystems, Tomcat implements the Servlet & JSP specifications and provides an environment for Java code to run in cooperation with a web server.