使用Servlet监听器动态更新select下拉列表

 html  layui +thymeleaf 内容是博客分类（自己正在写的这个博客需要用到这个）

<select id="blogTypeId" lay-verify="required" name="blogTypeId"lay-search><option value="selected"></option><option th:each="blogType:${application.blogTypeList}"th:value="${blogType.id}" th:text="${blogType.typeName}">博客类型A</option></select>

监听器 

实现 ServletContextListener接口达到初始化加载sleect option

但是每次更新需要重服务器，太麻烦，修改也不能及时自己更新

因为这个数据是放在application中的所有可以再实现一个接口ServletContextAttributeListener，再监听修改操作

监听器

package cn.edu.jxnu.blog.listener;import java.util.List;import javax.servlet.ServletContext;import javax.servlet.ServletContextAttributeEvent;import javax.servlet.ServletContextAttributeListener;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;import org.springframework.context.ApplicationContext;import org.springframework.stereotype.Component;import org.springframework.web.context.support.WebApplicationContextUtils;import cn.edu.jxnu.blog.domin.BlogType;import cn.edu.jxnu.blog.service.BlogTypeService;@Component/** * @Description 监听程序初始化 */public class InitBlogTypeData implements ServletContextAttributeListener,ServletContextListener {private static ApplicationContext applicationContext;public void contextInitialized(ServletContextEvent sce) {// 先获取servlet上下文ServletContext application = sce.getServletContext();// 获取spring web上下文applicationContext = WebApplicationContextUtils.getWebApplicationContext(application);// System.out.println("上下文："+applicationContext);BlogTypeService blogTypeService = applicationContext.getBean(BlogTypeService.class);// System.out.println("blogTypeService="+blogTypeService);List<BlogType> blogTypeList = blogTypeService.getBlogTypeData();application.setAttribute("blogTypeList", blogTypeList);System.out.println("ServletContextListener---（contextInitialized）...");}public void contextDestroyed(ServletContextEvent sce) {System.out.println("ServletContextListener---（contextDestroyed）...");}@Overridepublic void attributeAdded(ServletContextAttributeEvent args) {System.out.println("ServletContextAttributeListener---（attributeAdded）...");}/** * 后台更新分类数据的时候将清空ServletContext,此方法将监听，并重新添加blogTypeList */@Overridepublic void attributeRemoved(ServletContextAttributeEvent args) {// 先获取servlet上下文ServletContext application = args.getServletContext();// 获取spring web上下文applicationContext = WebApplicationContextUtils.getWebApplicationContext(application);// System.out.println("上下文："+applicationContext);BlogTypeService blogTypeService = applicationContext.getBean(BlogTypeService.class);// System.out.println("blogTypeService="+blogTypeService);List<BlogType> blogTypeList = blogTypeService.getBlogTypeData();application.setAttribute("blogTypeList", blogTypeList);System.out.println("ServletContextAttributeListener---（attributeRemoved）...");}@Overridepublic void attributeReplaced(ServletContextAttributeEvent args) {System.out.println("ServletContextAttributeListener---（attributeReplaced）...");}}

同时每次在controller的操作触发该监听 

controller方法签名类似这种，传入一个request 

@RequestMapping(value = "/delete")public String deleteBlog(@RequestParam(value = "ids", required = false) String ids,HttpServletResponse response, HttpServletRequest httpServletRequest)

在请求返回的同时触发监听器事件，清空或者改变application键值。 这里是选择直接删除

ServletContext application = httpServletRequest.getServletContext();application.removeAttribute("blogTypeList");

不过这样很麻烦每次都需要触发这个清空的事件才能更新。不过比重启服务器好多了。