Web容器启动后执行代码的几种方式
1.实现Servlet监听器接口ServletContextListener
package com.yli.init;import java.util.List;import java.util.Map;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;import org.springframework.web.context.WebApplicationContext;import com.suning.teach.service.ShopService;public class InitListener implements ServletContextListener { @Override public void contextDestroyed(ServletContextEvent context) { // 上下文销毁之后执行 } @Override public void contextInitialized(ServletContextEvent context) { // 上下文初始化执行 System.out.println("================>[ServletContextListener]自动加载启动开始."); // 读取Spring容器中的Bean[此时Bean已加载,可以使用] WebApplicationContext wac = WebContextUtil.getContext(); if (wac != null) { ShopService shopService = wac.getBean("shopService", ShopService.class); System.out.println("================>shopService[" + shopService + "]"); List<Map<String, Object>> shopList = shopService.findAllShop(); System.out.println("================>" + shopList); } System.out.println("================>[ServletContextListener]自动加载启动结束."); }}?
然后在web.xml文件配置该监听器
?
<listener><listener-class>com.yli.init.InitListener</listener-class></listener>
?
?
注意：从Spring IOC容器中读取Bean的工具类WebContextUtil
package com.yli.init;import org.springframework.web.context.ContextLoader;import org.springframework.web.context.WebApplicationContext;public class WebContextUtil { private static WebApplicationContext wac; public static WebApplicationContext getContext(){ if(null == wac){ wac = ContextLoader.getCurrentWebApplicationContext(); } return wac; }}?
2.实现Servlet的过滤器Filter
package com.yli.init;import java.io.IOException;import java.util.List;import java.util.Map;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import org.springframework.web.context.WebApplicationContext;import com.suning.teach.service.ShopService;public class InitFilter implements Filter { @Override public void destroy() { } @Override public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2) throws IOException, ServletException { } @Override public void init(FilterConfig config) throws ServletException { System.out.println("================>[Filter]自动加载启动开始."); // 读取Spring容器中的Bean[此时Bean已加载,可以使用] WebApplicationContext wac = WebContextUtil.getContext(); if (wac != null) { ShopService shopService = wac.getBean("shopService", ShopService.class); System.out.println("================>shopService[" + shopService + "]"); List<Map<String, Object>> shopList = shopService.findAllShop(); System.out.println("================>" + shopList); } System.out.println("================>[Filter]自动加载启动结束."); }}?
然后在web.xml文件配置过滤器即可
<filter><filter-name>InitFilter</filter-name><filter-class>com.yli.init.InitFilter</filter-class></filter><filter-mapping><filter-name>InitFilter</filter-name><url-pattern>/</url-pattern></filter-mapping>
?
?
3.编写一个Servlet,在web.xml里面配置容器启动后执行即可
import java.util.List;import java.util.Map;import javax.servlet.ServletConfig;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import org.springframework.web.context.WebApplicationContext;import com.suning.teach.service.ShopService;public class InitServlet extends HttpServlet { /** */ private static final long serialVersionUID = 1L; @Override public void init(ServletConfig config) { try { super.init(); } catch (ServletException e) { e.printStackTrace(); } System.out.println("================>[Servlet]自动加载启动开始."); // 读取Spring容器中的Bean[此时Bean已加载,可以使用] WebApplicationContext wac = WebContextUtil.getContext(); if (wac != null) { ShopService shopService = wac.getBean("shopService", ShopService.class); System.out.println("================>shopService[" + shopService + "]"); List<Map<String, Object>> shopList = shopService.findAllShop(); System.out.println("================>" + shopList); } System.out.println("================>[Servlet]自动加载启动结束."); }}?
然后在web.xml文件配置该Servlet的启动方式为：容器启动后执行
<servlet><servlet-name>InitServlet</servlet-name><servlet-class>com.yli.init.InitServlet</servlet-class><init-param><param-name>username</param-name><param-value>yli</param-value></init-param> <!-- 此处指定加载顺序为2,表明还有优先级更高的Servlet要先执行 --><load-on-startup>2</load-on-startup></servlet><servlet-mapping><servlet-name>InitServlet</servlet-name><url-pattern>/</url-pattern></servlet-mapping>
?关于启动后执行，由load-on-startup指定：
（1）当值为0或者大于0时，表示容器在应用启动时就加载这个servlet。值越小，启动优先级越高；
（2）当是一个负数时或者没有指定时，表示该servlet被调用时才加载。
?
4.如果你使用Spring IOC作为Bean管理容器，那么可以指定init-method
其中init-method表示bean加载成功后，立即执行某个方法。配置如下：start为要执行的方法名称
<!-- service --><bean id="shopService" init-method="start"><property name="shopDao" ref="shopDao" /></bean><!-- dao --><bean id="shopDao" ref="jdbcTemplate" /></bean>
?
Java代码如下
package com.yli.teach.service;import java.util.List;import java.util.Map;import com.yli.teach.dao.ShopDao;public class ShopService{ private ShopDao shopDao; // set 注入 public void setShopDao(ShopDao shopDao) { this.shopDao = shopDao; } /** * * 〈容器启动后执行方法〉 */ public void start(){ System.out.println("================>[init-method]自动加载启动开始."); List<Map<String, Object>> shopList = shopDao.findAllShop(); System.out.println("================>" + shopList); System.out.println("================>[init-method]自动加载启动结束."); }} ?
5.如果你使用Spring IOC作为Bean管理容器，还可以实现Spring的Bean后置处理器接口：BeanFactoryPostProcessor
表示：该Bean加载完成之后，Spring可以让开发者自定义一些事件，Java代码如下
package com.yli.init;import java.util.List;import java.util.Map;import org.springframework.beans.BeansException;import org.springframework.beans.factory.config.BeanFactoryPostProcessor;import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;import com.suning.teach.service.ShopService;public class KeyWordInit implements BeanFactoryPostProcessor { @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory factory) throws BeansException { System.out.println("================>[BeanFactoryPostProcessor]自动加载启动开始."); ShopService shopService = factory.getBean("shopService", ShopService.class); List<Map<String, Object>> shopList = shopService.findAllShop(); System.out.println("================>" + shopList); System.out.println("================>[BeanFactoryPostProcessor]自动加载启动结束."); }}?
这个Bean在xml文件做正常配置即可，如下
<bean id="keyWordInit" class="com.yli.init.KeyWordInit"></bean>
?
=================关于以上5种方式代码执行顺序的说明===================
4===>5===>1===>2===>3
即指定init-method的Bean开始执行
接着实现Spring的Bean后置处理器最先开始执行
然后是Servlet的监听器执行
再接下来是Servlet的过滤器执行
最后才是Servlet执行
?