Tomcat服務器自動加載監聽器

　　為避免前台顯示權限菜單是每次都從數據庫中讀取，使用ServletContextListener在服務器啟動和關閉時創建和關閉緩存。

　　在web.xml配置監聽器:

<!-- 配置用於初始化數據的監聽器，一定要配置在spring的ContextLoaderListener之后 -->
    <listener>
    <listener-class>com.itcast.oa.util.InitListener</listener-class>
    </listener>    

　　監聽器類：

@Component
public class InitListener implements ServletContextListener{
    
    @Resource
    private PrivilegeService privilegeService;
    
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        List<Privilege> topPrivilegeList = privilegeService.findTopList();
        sce.getServletContext().setAttribute("topPrivilegeList", topPrivilegeList);
        System.out.println("=====已准備數據======");
    }

　　實際上，Tomcat不能檢測到Spring容器，而是通過反射生成監聽器實例，而將監聽器類注入到Spring中，Spring容器里面也存在一個監聽器實例，Tomcat自己創建的實例根本用不了Spring注入的內容，所以不能采用注入的方式。

下面是修改：

public class InitListener implements ServletContextListener{
    
    
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        
        //獲取容器和相關的Service
        ApplicationContext ac = WebApplicationContextUtils.getWebApplicationContext(sce.getServletContext());
        PrivilegeService privilegeService = (PrivilegeService)ac.getBean("privilegeServiceImpl");
        List<Privilege> topPrivilegeList = privilegeService.findTopList();
        sce.getServletContext().setAttribute("topPrivilegeList", topPrivilegeList);
        System.out.println("=====已准備數據======");
    }