Advanced Java Programming (J2EE) - Servlets - Lab exercise - Hello World Servlet 31242/32549/ J2EEAdvanced Internet Programming INFO: What's New FAQ Software Machines Oracle Assignments MODULES: 00 Admin 01 Intro 02 Architecture 03 Servlets 04 JSP 05 JDBC 06 RMI 06 JNDI 07 EJB 08 XML 08 Web Services 09 Security 10 Transactions 11 Legacy 12 Review 99 Design LINKS: START page Faculty of IT UTS Module: Servlets Tutorial exercise - Creating a WAR file manually This laboratory exercise involves developing a Hello World servlet, step by step. It is a long process, but each step should be simple enough. Take careful note of what you are doing at each step, and the commands you need to run. It gets easier once you've worked out the process - your first servlet will be your hardest! Level of Difficulty: 1 (easy) Estimated time: 30 minutes Pre-requisites: Run 'wlenv' to set your environment correctly Start your WebLogic server running in the background Manually creating a servlet This exercise will lead you step by step through writing and deploying your first Java servlet without an Integrated Development Environment (IDE) such as Eclipse. Create a directory to store your source code. This directory should be completely outside the WebLogic server directory hierarchy, e.g. cd mkdir aip mkdir aip/servlets mkdir aip/servlets/helloworld cd aip/servlets/helloworld Create a file called HelloWorldServlet.java with the following contents. If you are familiar with Unix, try the 'vi' editor, e.g. vi HelloWorldServlet.java import javax.servlet.*; import javax.servlet.http.*; import java.io.*; public class HelloWorldServlet extends HttpServlet { public void doGet (HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { res.setContentType("text/plain"); PrintWriter out = res.getWriter(); out.println("Hello servlet world!"); out.close(); } } Compile your source code using javac. javac HelloWorldServlet.java If you see an error message that it cannot import the servlet packages (javax.servlet and javax.servlet.http), then your environment is not set correctly. Go back and re-run setEnv.sh. Congratulations, you have just written your first Java servlet. Before you can run it though, you must first package it, and deploy it. These steps are described below. Packaging your servlet 1: directory structure Java servlets execute as part of a web server. You cannot run or test them from the command line. The web server you will use to run your servlet is the web server built in to the application server (WebLogic). To "run" your servlet, you will access a URL in your web browser. This is quite similar to running a CGI program, or running a PHP script. Before you can install your servlet into the application server, it needs to be packaged properly. Servlets are part of what J2EE calls 'web applications', and web applications should be packaged in a Web Application Archive file, or WAR file. A WAR file is basically a compressed zip file that contains all parts of your web application. The parts may include: static web site files (HTML, GIF, JPEG, CSS, etc) Java servlets a deployment descriptor (described later) Importantly, when you package your application as a WAR file, it must follow a particular directory structure. Starting at the same directory where your HelloWorldServlet.java file is, run the following commands. Note that the directory names are case-sensitive, so be careful to type them correctly. mkdir WEB-INF mkdir WEB-INF/classes Your compiled Java servlet class files must be placed in the WEB-INF/classes directory. When you compiled your HelloWorldServlet earlier, you just put the .class file in the same directory as the .java file. You'll need to fix that now. rm *.class javac -d WEB-INF/classes HelloWorldServlet.java Note the use of the '-d' option to javac, which allows you to specify the output directory (where the .class files go). Packaging your servlet 2: deployment descriptor As mentioned above, a WAR file contains static HTML (etc) files, Java servlet classes, and a deployment descriptor. The next step is for you to create a deployment descriptor. A deployment descriptor is an XML file describing the properties of your 'web application'. When your web application includes servlets, the deployment descriptor file describes the name of each servlet, and what URL should be used to invoke the servlet. In the case of web applications, the deployment descriptor is contained in a file called web.xml, and it must be placed in the WEB-INF directory. Edit the web.xml file now, e.g. vi WEB-INF/web.xml (or use the text editor of your choice). Into the web.xml file, copy the following text:   HWServlet HelloWorldServlet HWServlet /HW Points to note about the definitions in web.xml: servlet-name can be any name you choose. It does not have to be the same as the filename in which the servlet class is stored. Every servlet referenced in your web.xml must have a unique servlet-name within that one web.xml file. servlet-class specifies the name of the Java class file containing the compiled servlet code. url-pattern specifies the URL by which you want users to be able to execute your servlet. In the example shown above, the url-pattern is "/HW", so the URL that will be used to invoke the servlet will look like http://hostname:7001/HelloWorldApp/HW Packaging your servlet 3: static HTML files Your WAR file can also include static HTML files, as well as images (GIF, JPEG), style sheets (CSS), and any other static files you would expect to find on a web server. In the WAR file, these files must be placed outside the WEB-INF directory. Any files not in the WEB-INF directory can be accessed through the web browser. Any files that are inside the WEB-INF directory (including your web.xml deployment descriptor, and your servlet class files) will be protected, and not accessible to users over the web. Let's create a static HTML file called index.html to go inside your WAR file. It can go in the top-level directory of your web application (i.e. the directory that has the WEB-INF subdirectory in it). Use a text editor to create index.html with the following contents:

My first WAR file

Run my Hello World servlet.

Packaging your servlet 4: final check When creating WAR files, it is very important that everything is in the correct directory. So before we actually create the WAR file, take a moment to check when you view your directory hierarchy, it looks something like the following: $ ls -1F HelloWorldServlet.java WEB-INF/ index.html $ ls -1F WEB-INF classes/ web.xml $ ls -1F WEB-INF/classes HelloWorldServlet.class i.e. the directory tree structure should look like: - index.html - HelloWorldServlet.java / WEB-INF - web.xml / classes - HelloWorldServlet.class Note that it is not essential to have your Java source code file as part of the WAR file, but it is convenient to keep all the files together. Packaging your servlet 5: create the WAR file Finally, you are ready to create your WAR file. Run the following command, which will create a file called HelloWorldApp.war in the parent directory of where you execute it from. jar cf ../HelloWorldApp.war * In the above command, the "c" means "c"reate a WAR file. Now view the contents of your WAR file to ensure that the file was created correctly. Run the following command to list the WAR file contents: jar tf ../HelloWorldApp.war In the above command, the "t" means to show the "t"able-of-contents of the WAR file. The output from the previous command should show something like: META-INF/ META-INF/MANIFEST.MF HelloWorldServlet.java WEB-INF/ WEB-INF/classes/ WEB-INF/classes/HelloWorldServlet.class WEB-INF/web.xml index.html The META-INF directory and the MANIFEST.MF file are automatically added by the jar utility. You can ignore them. Deploying your web application Now that you have a WAR file, you can "deploy" it to the web server. Deployment is the process of installing an application. In WebLogic, there are a variety of ways you can deploy an application. The simplest is just to copy your WAR file into your WebLogic server's "autodeploy" directory. cp ../HelloWorldApp.war ~/weblogic/autodeploy You can do this when the server is running. The server checks the contents of the autodeploy directory every few seconds, and when it sees a new WAR file, or one with an updated timestamp, it automatically deploys (or redeploys) it. Testing your web application If you have followed the steps above exactly, try accessing your application through the following URL: http://localhost:7001/HelloWorldApp/ It should show you the contents of your index.html file. If you click on the link to your servlet, it should execute your servlet and display the servlet's "Hello World" message. Note that when you deployed your WAR file into WebLogic, it created a virtual directory under the root of your web server with the same name as your WAR file. So the name you choose for your WAR files is important, because the WAR filename will become part of the URL. Reflection Take note of what was required to write a single servlet, package it in a WAR file, and deploy it to the web server. Note the commands, and the directory structure used. When you go to create your second servlet, you might find it easier to set up the directory structure first before beginning to write any Java source code. You will also probably find it convenient to copy your web.xml file and simply edit the values inside. You might even like to create yourself a Makefile, or a shell script which automates the process of compiling, packaging and deploying your WAR file. © 2008 University of Technology, Sydney. All Rights Reserved. Redistribution without permission prohibited.