GWT Eclipse: Using classes from other projects causes "Server class & hellip; could not be found in the Web application, but was found on the classpath system


I'm newbie in developing with GWT. I started to maintain a GWT (2.7) application and need to revise the logging. So I decided to make use of MDC (MappedDiagnosticContext) and wrote a servlet Filter to put the user name in MDC, like this:

public class MDCServletFilter implements Filter {

    /* (non-Javadoc)
     * @see javax.servlet.Filter#destroy()
    public void destroy() {}

    /* (non-Javadoc)
     * @see javax.servlet.Filter#doFilter(javax.servlet.ServletRequest, javax.servlet.ServletResponse, javax.servlet.FilterChain)
    public void doFilter(ServletRequest aRequest, ServletResponse aResponse, FilterChain aFilterChain)
            throws IOException, ServletException {
        try {
            // get the session from the request ...
            HttpServletRequest tempRequest = (HttpServletRequest)aRequest;
            HttpSession tempSession = tempRequest.getSession();
            // get the currently logged in user ...
            String tempUser = (String)tempSession.getAttribute(Authorizer.USER_KEY);
            // if user is logged in, put the name into the MDC ...
            if (tempUser != null && tempUser.trim().length() > 0) {
                MDC.put(Authorizer.USER_KEY, tempUser);
            // at least call the other filter ..
            aFilterChain.doFilter(tempRequest, aResponse);
        } finally {
            // finally remove the user name from the MDC ...

    /* (non-Javadoc)
     * @see javax.servlet.Filter#init(javax.servlet.FilterConfig)
    public void init(FilterConfig arg0) throws ServletException {}


The web.xml:

    <!-- MDC Filter -->
    <!-- MDC Filter END -->

Now when I start the application in my eclipse (June) I get the warning:

[WARN] Server class '' could not be found in the web app, but was found on the system classpath

The filter class resides in a "common" project, not in the GWT project, because we have some more GWT projects which make use of some common classes. If I put the filter class in to the GWT project, no warning occur.

So, how do I have to setup the GWT project to use other project's classes without any warnings?

Thanks in advance!

The details depend on your build tool and/or IDE, but the goal is to have all server-side classes in the webapp's WEB-INF (either in WEB-INF/classes, which is probably the case for your GWT project, or in a JAR in WEB-INF/lib).

This will be necessary anyway when deploying the webapp to a servlet container (unless you intend to deploy your "common" project as a shared lib in your servlet container).