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Below is a step-by-step tutorial to a hello world servlet that writes out some HTML to the user who visits it. 

**Please note that in the following examples, you will need to replace "username" with your actual username**

Actually visiting http://students.cs.ndsu.nodak.edu/~username/ will bring you to an example site.
Visiting http://students.cs.ndsu.nodak.edu/~username/servlet/HelloWorld will bring you to the servlet that this howto will create.


====== Howto: A Hello World Servlet ======

===== Making sure the server works =====

==== Making sure your web page works ====

The first step is to make sure your web page works. 

Check to make sure you have a working web page by visiting http://students.cs.ndsu.nodak.edu/~username. See instructions [[deptlab:webpage|here]] for help with setting up your web page.

==== Making sure Tomcat works ====

You will also want to make sure that your account is configured to use Tomcat. Take the simple JSP page below and put it in your public_html directory somewhere and browse to it. 

For example, if I were to place the sample JSP page at /home/helsene/public_html/java.jsp, I could access it as http://students.cs.ndsu.nodak.edu/~helsene/java.jsp

<code>
<html>
<head> <title> Test JSP </title> </head>
<body> <%= new java.util.Date().toString() %> </body>
</html>
</code>

So your JSP works now? Great! If this simple test page doesn't work, contact [[robefoer@cs.ndsu.edu|the departmental administrator]] to get your account configured to use Tomcat.  If you are enrolled in CSCI 366, your account has already been configured with Tomcat access.

===== Compiling a basic servlet =====

==== The program ====

This servlet is a short little 'Hello World'

We will be creating a java class file that acts as our servlet, but before we compile it, we need to write it first!

<code>
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class HelloWorld extends HttpServlet {

        public void doGet(HttpServletRequest request, HttpServletResponse response)
        throws IOException, ServletException
        {
                response.setContentType("text/html");
                PrintWriter out = response.getWriter();
                out.println("<html>");
                out.println("<head>");
                out.println("<title>Hello World!</title>");
                out.println("</head>");
                out.println("<body>");
                out.println("<h1>Hello World</h1>");

                out.println("<br/>");
                out.println("This HTML is generated by a servlet, the code for it is located <a href=\"/~username/HelloWorld.java\">here.</a>");
                out.println("</body>");
                out.println("</html>");
        }
}

</code>

Save this class as HelloWorld.java in any folder of your choosing. 
==== Compiling a servlet ====

Compiling is a bit trickier. You will need {{:classes:csci366:servlet-api.zip|the servlet api jar file}} in order to compile. This file is located in /opt/lablibs/servlet-api.jar in the lab, so if you're using the lab to compile, you can just use: javac -cp "./:/opt/lablibs/servlet-api.jar" <name>.java. 

If you're not in the lab, you'll need to adjust your classpath or import the .jar into Netbeans of Eclipse. Instructions for doing that can be found [[classes:csci366:loading_libraries|here]].

Download servlet-api.jar from the link above and save it somewhere handy. 
Assuming I saved the servlet-api.jar and the HelloWorld.java files in my home directory (/home/username/) I could compile the HelloWorld.java file using the command: 
<code>
javac HelloWorld.java
</code>


Now we've got a HelloWorld.class, now what do we do with it?

===== Setting up Tomcat to use our servlet =====

==== Putting your class in the right folder ====

So now we need to make a folder called //classes//. This folder needs to be in public_html/WEB-INF/. All of your servlet classes go in here, so copy the compiled HelloWorld.class file into public_html/WEB-INF/classes/. 

At this point you should have the files/folders:
<code>
/home/username/public_html/
/home/username/public_html/WEB-INF/
/home/username/public_html/WEB-INF/classes/
/home/username/public_html/WEB-INF/classes/HelloWorld.class
</code>

==== The web.xml file ====

Tomcat needs to look for servlets in a special WEB-INF folder. You should create this in your public_html folder. 

The WEB-INF folder needs to contain a web.xml file which tells Tomcat where and how to access the servlet. 

=== Example web.xml ===
For this howto, we can use this web.xml file:
<code>
<web-app>
   <servlet>
      <servlet-name>Hello World</servlet-name>
      <servlet-class>HelloWorld</servlet-class>
   </servlet>
   <servlet-mapping>
      <servlet-name>Hello World</servlet-name>
      <url-pattern>/servlet/HelloWorld</url-pattern>
   </servlet-mapping>
</web-app>
</code>

^XML tag name^Purpose^
|servlet|This defines the servlet, you can set a name and the classfile to be associated with that name|
|servlet-mapping|This maps a URL to a servlet using the servlet's name (that you defined in <servlet>)|
|servlet-name|An arbitrary name to define your servlet (must be consistent throughout the entire web.xml)|
|servlet-class|The name of the class file, if your class is called 'HelloWorld.class', you will use 'HelloWorld'|
|url-pattern|The path portion of the URL to access your servlet. If you want to access your servlet at 'http://students.cs.ndsu.nodak.edu/~username/servlet/HelloWorld', then this will be '/servlet/HelloWorld'|

This file defines a servlet called //Hello World//, tells Tomcat to use the class //HelloWorld// and says that it will be accessed by the URL /servlet/HelloWorld. The full URL in this case will be: http://students.cs.ndsu.nodak.edu/~username/servlet/HelloWorld

You can copy this and use this web.xml in your servlet, just change the values to match your servlet. Servlet-name can be any name of your choosing, servlet-class needs to be the package and class name of the class you want to use, and url-pattern defines which URL you want to use to access the servlet.

=== Where does web.xml go? ===
This web.xml file needs to be placed at public_html/WEB-INF/web.xml for Tomcat to see it. So make the web.xml file and use the example above

The files/folders we should have now look like:
<code>
/home/username/public_html/
/home/username/public_html/WEB-INF/
/home/username/public_html/WEB-INF/web.xml
/home/username/public_html/WEB-INF/classes/
/home/username/public_html/WEB-INF/classes/HelloWorld.class
</code>


You should check out http://students.cs.ndsu.nodak.edu/~username/servlet/HelloWorld, replacing "username" with your actual username. If this doesn't work, double check the steps above. If everything looks fine and it doesn't work after 5 minutes, then Tomcat did not load your servlet correctly. Send me an [[robefoer@cs.ndsu.edu|email]] and I can investigate.