获取webroot

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必须能够获取ServletContext,在servlet中可以.

private String makeFilePath(){
  final String dir = "photos";
  String root  = this.getServlet().getServletContext().getRealPath("/");
  logger.debug("webroot = {}", root);
        if(null != root && !"".equals(root.trim())){
            return new File(root + dir).getAbsolutePath();
        }
        return null;
 }