code: public static String getWebRoot()
  	{
  		if (webroot != null) {
  			return webroot;
  		}
  		try
  		{
  			String path = BeetlUtil.class.getClassLoader().getResource("").toURI().getPath();
  			if (path == null)
  			{
  				throw new RuntimeException("Beetl未能自动检测到WebRoot，请手工指定WebRoot路径");
  			}
  			File file = new File(path);
  			String root = null;
  			if(file.getParentFile()!=null&&file.getParentFile().getParentFile()!=null) {
  				root = file.getParentFile().getParentFile().getCanonicalPath();
  			}else {
  				throw new RuntimeException("Beetl检测到Beetl.jar位于"+path+"但未能自动检测到WebRoot，请手工指定WebRoot路径");
  			}
  			
  			return root;
  		}
  
  		catch (IOException e)
  		{
  			throw new RuntimeException(e);
  		}
  		catch (URISyntaxException e)
  		{
  			throw new RuntimeException(e);
  		}
  
  	}
docs: 返回Web根路径,如果存在自定义webroot路径,则返回自定义webroot