此问题出现在GWT2.6.1中，可能已在后续版本中得到解决。为了处理GWT2.6.1，JettyLauncher.java在gwt-dev.jar中定制www.example.com，通过Filter为8888端口的源Map请求检索并返回9999端口的源，并将该类添加到project中，将其放在src中使用即可处理。

com.google.gwt.dev.shell.jetty.JettyLauncher.java（custom.添加wac.addFilter（））

protected JettyServletContainer createServletContainer(TreeLogger logger,
      File appRootDir, Server server, WebAppContext wac, int localPort) {
      wac.addFilter(SourcemapFilter.class, "/sourcemaps/GwtModule/gwtSourceMap.json", EnumSet.of(DispatcherType.INCLUDE,DispatcherType.REQUEST));
      return new JettyServletContainer(logger, server, wac, localPort, appRootDir);
  }

com.google.gwt.dev.shell.jetty.SourcemapFilter.java（custom.新类）

public class SourcemapFilter implements Filter {

    @SuppressWarnings("unused")
    @Override
    public void init(FilterConfig arg0) throws ServletException {
        // noop
    }

    @SuppressWarnings("unused")
    @Override
    public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) arg0;
        HttpServletResponse response = (HttpServletResponse) arg1;
        String proxyURL =
                "http://" + request.getServerName() + ":" + System.getProperty("gwt.codeserver.port") + request.getRequestURI();
        System.out.println("[Sourcemap proxy filter] proxyURL: " + proxyURL);
        URL url = new URL(proxyURL);
        InputStream is = url.openStream();
        int value;
        while ((value = is.read()) != -1) {
            response.getWriter().write(value);
        }
        is.close();
    }

    @Override
    public void destroy() {
        // noop
    }

}