1. <!--对于重复利用的页面，需要使用th:fragment -->
    2. <nav class="navbar navbar-dark sticky-top bg-dark flex-md-nowrap p-0" th:fragment="topbar">
    3.     <a class="navbar-brand col-sm-3 col-md-2 mr-0" href="http://getbootstrap.com/docs/4.0/examples/dashboard/#">[[${session.loginName}]]</a>
    4.     <input class="form-control form-control-dark w-100" type="text" placeholder="Search" aria-label="Search">
    5.     <ul class="navbar-nav px-3">
    6.         <li class="nav-item text-nowrap">
    7.             <a class="nav-link" href="http://getbootstrap.com/docs/4.0/examples/dashboard/#">Sign out</a>
    8.         </li>
    9.     </ul>
    10. </nav>
    12. <!--thymeleaf可以使用变量，而变量的值可以从引入公共页面的页面的中获取-->
    13. <a class="nav-link" th:class="${activeUrl=='main'}?'nav-link active':'nav-link'" href="http://getbootstrap.com/docs/4.0/examples/dashboard/#">
    14.   <svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="feather feather-home">
    15.     <path d="M3 9l9-7 9 7v11a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2z"></path>
    16.     <polyline points="9 22 9 12 15 12 15 22"></polyline>
    17.   </svg>
    18.   Dashboard <span class="sr-only">(current)</span>
    19. </a>
    21. <!--引入公共页面   公共页面的位置::fragment的值 -->
    22. <div th:replace="common/bar::sidebar(activeUrl='list')"></div>