GWT Eclipse: using classes from other projects cause "Server class ... could not be found in the web app, but was found on the system classpath

Question

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 ...
            MDC.remove(Authorizer.USER_KEY);
        }
    }

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

}

The web.xml:

<web-app>
    <!-- MDC Filter -->
    <filter>
        <filter-name>MDCServletFilter</filter-name>
        <filter-class>
            foo.bar.filter.MDCServletFilter
        </filter-class>
    </filter>
    <filter-mapping>
        <filter-name>MDCServletFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
    <!-- MDC Filter END -->

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

[WARN] Server class 'foo.bar.filter.MDCServletFilter' 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!

Answer 1

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).

Answer 2

I solved it by linking the source folder of the common project into the GWT project:

GWT Project's Properties -> JavaBuild Path -> "Link source..." ->

setting the "Linked folder location:" to "WORKSPACE_LOC/someSecondProject/src", then renaming "Folder name:" from "src" to e.g. "CommonGWT.src".

This settings compile all the sources of the other project into "WEB-INF/classes" of the GWT project and the Eclipse GWT is satisfied.