In the deployment descriptor, you must also include a <servlet> tag, which allows you to specify the fully-qualified class name of the servlet. You have only posted the <servlet-mapping> tag in your forum post.
In order to actually send the HTTP request using the URLConnection class, I think that you have to call getInputStream(). This will send the request and allow you to access the body of the response.
Also, I see that you are setting the request's content type...since you are not putting anything in the request body, you do not need to do this. The servlet will still accept your request just fine.
In addition,
you should not be overriding init(ServletConfig). The method you should override is init().