jsp条件判断
<c:choose>
<c:when test="${username == null }">
<!-- 未登录 -->
<a href="login">你好,请登录</a>
<a href="reg">注册</a>
</c:when>
<c:otherwise>
<!-- 顶部已登录 -->
<span style="font-size:12px;">欢迎你![ ${username.user_name } ]</span>
<a href="../logout">安全退出</a>
<a href="../personalcenter">个人中心</a>
</c:otherwise>
</c:choose>