Learning Java, 4th Edition

Java Web Applications

So far we’ve used the term web application generically, referring to any kind of browser-based application that is located on a web server. Now we are going to be more precise with that term. In the context of the Java Servlet API, a web application is a collection of servlets and Java web services that support Java classes, content such as HTML or JSP pages and images, and configuration information. For deployment (installation on a web server), a web application is bundled into a WAR file. We’ll discuss WAR files in detail later, but suffice it to say that they are really just JAR archives that contain all the application files along with some deployment information. The important thing is that the standardization of WAR files means not only that the Java code is portable, but also that the process of deploying the application to a server is standardized.

Most WAR archives have at their core a web.xml file. This is an XML configuration file that describes which servlets are to be deployed, their names and URL paths, their initialization parameters, and a host of other information, including security and authentication requirements. In recent years, however, the web.xml file has become optional for many applications due to the introduction of Java annotations that take the place of the XML configuration. In most cases, you can now deploy your servlets and Java web services simply by annotating the classes with the necessary information and packaging them into ...