...
    public class ExpiresFilter implements Filter {

	private static final String CACHE_CONTROL = "Cache-control"; //$NON-NLS-1$
	private static final String MAX_AGE_10000 = "max-age=10000"; //$NON-NLS-1$
	private static final String PRAGMA = "Pragma"; //$NON-NLS-1$
	private static final String EXPIRES = "Expires"; //$NON-NLS-1$
	private static final String RWT_RESOURCES_THEMES_IMAGES = "rwt-resources/themes/images/"; //$NON-NLS-1$
	private static final String RWT_RESOURCES_GENERATED = "rwt-resources/generated"; //$NON-NLS-1$

	@Override
	public void init(FilterConfig filterConfig) throws ServletException {
	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		
		chain.doFilter(request, response);
		
		HttpServletRequest req = (HttpServletRequest) request;
		HttpServletResponse res = (HttpServletResponse) response;
		if (req.getRequestURL() != null 
				&& (req.getRequestURL().indexOf(RWT_RESOURCES_GENERATED) >= 0
				|| req.getRequestURL().indexOf(RWT_RESOURCES_THEMES_IMAGES) >= 0)) {
			res.setDateHeader(EXPIRES, (new GregorianCalendar(3000, 1, 1)).getTime().getTime());
			res.setHeader(PRAGMA, MAX_AGE_10000);
			res.setHeader(CACHE_CONTROL, MAX_AGE_10000);
		}
	}

	@Override
	public void destroy() {
	}
...

...
        <filter>
	 <filter-name>ExpiresFilter</filter-name>
	 <filter-class><your package>.ExpiresFilter</filter-class>
	</filter>
	
	<filter-mapping>
	 <filter-name>ExpiresFilter</filter-name>
	 <url-pattern>/*</url-pattern>
	</filter-mapping>
...