Java™ Application Development on Linux - Dator

410Chapter 18Servlets: Java Pressed into Service/*** Returns a short description of the servlet.*/public StringgetServletInfo(){return "Very Simple Servlet";} // getServletInfo()} // class HiServletWhew! That is a lot of code for only a simple “Hello, world,” but rememberthat this is not just a run-on-your-desktop application. This is a networkbasedservlet that can respond to concurrent requests from across the networkand talk to Web browsers. There’s a lot of plumbing that needs to be connectedto a Web server for the servlet to run, and that’s what most of this code is—justthe connections. The other verbose part is all of the HTML that we spit outaround our message. You can make it even more elaborate, with backgroundcolors and other HTML decorations if you want to try it yourself.Once you’ve written a servlet, though, you can’t just run it from thecommand line like any Java class. 1 Much of the work of a servlet is done behindthe scenes by the Web server (e.g., Tomcat). The tougher question is, “Howdo you run a servlet?” That involves issues of configuring the Web server, settingup directory locations, and so forth. It’s the subject of the next chapter.Once you’ve deployed this servlet (by reading the next chapter and/or withhelp from your IDE), you can run the servlet and talk to it via your browser.We’ve pointed a browser window at one such deployment to get a highly uninterestingWeb page (Figure 18.2) whose HTML source (in your browser menu,select View>Page Source) is shown in Figure 18.3.1. Well, actually, you could if it had a main() method defined. Our example doesn’t, but aservlet class is still a Java class, and you might define a public static void main()method that would allow you to run it from the command line as a way to drive the rest of theclass for simple testing. Of course, such a simple test harness wouldn’t be driving a Webbrowser, and so on but technically it is possible. We didn’t want to lie to you.