code: public String getPosterUrl() {
  		Image poster = getComponentModel().poster;
  
  		if (poster == null) {
  			return null;
  		}
  
  		// this variable needs to be set in the portlet environment.
  		String url = getEnvironment().getWServletPath();
  		Map<String, String> parameters = getBaseParameterMap();
  		parameters.put(POSTER_REQUEST_PARAM_KEY, "x");
  		return WebUtilities.getPath(url, parameters, true);
  	}
docs: Creates a dynamic URL that the poster can be loaded from. In fact the URL points to the main application servlet,
  but includes a non-null for the parameter associated with this WComponent (ie, its label). The handleRequest
  method below detects this when the browser requests a file.
  
  @return the url to load the poster from, or null if there is no poster defined.