[FIXED] Servlets and AJAX communication

Issue

I do have a communication problem here between my Java servlet and an Ajax request. more about it:

Absolute path to the index.html (including JavaScript/Ajax request): http://localhost:9080/chat/index.html

In the same folder the servlet: MyChat.class

And the Request is working like this:

var url = "http://localhost:9080/chat";

var name = document.getElementById("username").getAttribute("value");
var message = document.getElementById("message").getAttribute("value");

var tosend = name+","+message;

request.open('GET', url, true);
request.send(tosend);
request.onreadystatechange = interpretRequest;

I'm having a formula where a user just types in the name and the message and username and message are <input> tags in my HTML file. The Ajax request works, that's sure, but it doesn't communicate with the servlet. I also don't have an idea where the output from System.out.println() goes. No log file is filled... And the servlet looks like this:

public class MyChat extends HttpServlet
{
    private static final long serialVersionUID = 1L;
    
    private ArrayList<String> myMessages = new ArrayList<String>();
    
    public void doGet(HttpServletRequest request, HttpServletResponse response)
                        throws IOException, ServletException
    {
        BufferedReader r = request.getReader();

        while(r.readLine() != null)
        {
                        // split the words at the ','
            String[] tmp = r.readLine().split(".\\s");
            myMessages.add(tmp[0]+" "+tmp[1]);
        }
                
        //response.setContentType("text/html");
        PrintWriter out = response.getWriter();

                Iterator<String> it = myMessages.iterator();
        while(it.hasNext())
        {
            out.println(it.next());
                        System.out.println(it.next());
        }
    }
    
    public void doPost(HttpServletRequest request, HttpServletResponse response)
                        throws IOException, ServletException
    {
        doGet(request, response);
    }
}

Solution

The URL you've specified isn't to your servlet.

Just like the URL to the index page is http://<server>:<port>/<webapp name>/<resource> the URL to your servlet needs a mapping in the web.xml file that corresponds to the <resource> part of the url.

For example, if you had a controller servlet you'd expect something like the following in your web.xml:

<servlet>
  <servlet-name>controller</servlet-name>
  <servlet-class>ControllerServlet</servlet-class>
</servlet>

<servlet-mapping>
  <servlet-name>controller</servlet-name>
  <url-pattern>/*.do</url-pattern>
</servlet-mapping>

The URLs that would invoke the 'controller' servlet would then follow the form http://<server>:<port>/<webapp name>/<anything>.do.

Answered By - Nick Holt
Answer Checked By - David Marino (JavaFixing Volunteer)