A Servlet container requires every Java web application to have a certain structure so that it can manage the application properly. Here is the outline of such a structure:

Perhaps the most important part of it is the WEB-INF directory. It is the brain and heart of a Java web application. The contents of this directory are protected by the servlet container—it prevents anyone from navigating to, say, http://www.someserver.com/myapp/WEB-INF/ and seeing what this directory contains.

The WEB-INF/classes subdirectory is where the compiled Java classes go—those classes that we create for our application, such as page classes.

The WEB-INF/lib subdirectory is for the libraries used by the application, such as the Tapestry framework libraries. Any class or resource stored here should normally be packaged in a JAR file.

The web.xml file which must be present inside the WEB-INF directory is a deployment descriptor—it is described in the next section. Also, the WEB-INF directory can contain other files as needed by the application.

There can be another hidden directory in a Java web application, META-INF. It can contain other useful information about the application.

All the other files and directories, those outside WEB-INF and META-INF , are accessible from the Web. This means that if we have have a JSP page named somePage.jsp, it can be seen by anyone by navigating to something like http://www.someserver.com/myapp/somePage.jsp. Typically you will find here HTML and JSP pages as well as images and stylesheets. Naturally, they all can be put into as many different directories as is convenient.

Returning to the web.xml file, we never had any need to look into it in the course of the book, so it is actually not necessary to know its contents. But sometimes such knowledge can be useful, so let's have a look into deployment descriptor.