分两步：
为组件命名调用组件具体实施：
th:fragment="main"<div th:insert="~{commons :: main}">...</div>例子：
<!--顶部状态栏--> <nav class="navbar navbar-dark sticky-top bg-dark flex-md-nowrap p-0" th:fragment="headbar"> <a class="navbar-brand col-sm-3 col-md-2 mr-0" href="http://getbootstrap.com/docs/4.0/examples/dashboard/#">[[ ${session.username} ]]</a> <input class="form-control form-control-dark w-100" type="text" placeholder="Search" aria-label="Search"> <ul class="navbar-nav px-3"> <li class="nav-item text-nowrap"> <a class="nav-link" href="http://getbootstrap.com/docs/4.0/examples/dashboard/#">Sign out</a> </li> </ul> </nav> <div th:insert="~{commons/commons::headbar}"></div>