Introduction to Java EE

You've inherited an enterprise Java application. The code compiles on your colleague's machine, but not on yours. You copy a servlet example you found on a forum, and the javax.servlet.http.HttpServlet import stays stubbornly red in your editor. You download Tomcat, deploy your archive, and the server returns a 404 on a URL you're certain you declared.

These three symptoms have the same cause, and it isn't technical: it's political. In 2017, Oracle transferred Java EE to the Eclipse Foundation. The foundation obtained the code, the compatibility tests, and the specifications, but not the javax trademark. As a result, all of the platform's packages were renamed to jakarta. The web is now full of tutorials written before this change, whose code will never compile in a modern project.

This lesson gives you the lay of the land: what the platform actually is, how its specifications fit together, the difference between a web container and a full application server, and above all how to tell at a glance whether a code example you're reading is usable or outdated. By the end, you'll have a Maven project that produces a deployable WAR archive.