test

    public void dropDown_pre_processValueChange(ValueChangeEvent event) {
        Object image = dropDown_pre.getSelected();
//        String imageURL = Constants.IMAGE_PATH  + image;
//        HttpServletRequest request = (HttpServletRequest) this.getExternalContext().getRequest();
        String testURL = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + "/" + request.getContextPath() + "/" + request.getServletPath() + "/" + "resources" + "/" + "image" + "/" + "appicons" + "/" + image;
        image_pre.setVisible(true);
        image_pre.setUrl(testURL);
    }