应用上下文对象是通过 new ClassPathXmlApplicationContext(Spring配置文件) 方式获取的，但是每次从容器中获取Bean时都要编写 new ClassPathXmlApplicationContext(Spring配置文件)，这样的弊端是配置文件加载多次，应用上下文对象创建多次。
在Web项目中，可以使用ServletContextLIstener监听Web应用的启动，我们可以在Web应用启动时，就加载Spring的配置文件，创建应用上下文对象ApplicationContext，再将其存储到最大的域servletContext域中，这样就可以在任意位置获取应用上下文ApplicationContext对象。
1、创建监听器
package com.ntect.listener; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; import javax.servlet.ServletContext; import javax.servlet.ServletContextEvent; import javax.servlet.ServletContextListener; public class ContextLoaderListener implements ServletContextListener { public void contextInitialized(ServletContextEvent sce) { ServletContext servletContext = sce.getServletContext(); //读取web.xml中的全局参数 String contextConfigLocation = servletContext.getInitParameter("contextConfigLocation"); ApplicationContext app = new ClassPathXmlApplicationContext(contextConfigLocation); //将Spring的应用上下文对象存储到ServletContext域中 servletContext.setAttribute("app",app); System.out.println("spring容器创建完毕...."); } public void contextDestroyed(ServletContextEvent sce) { } }
2、创建获取applicationContext对象的工具类
package com.ntect.listener; import org.springframework.context.ApplicationContext; import javax.servlet.ServletContext; public class WebApplicationContextUtils { public static ApplicationContext getWebApplicationContext(ServletContext servletContext) { return (ApplicationContext)servletContext.getAttribute("app"); } }
3、创建servlet的测试类
package com.ntect.web; import com.ntect.listener.WebApplicationContextUtils; import com.ntect.service.UserService; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; public class UserServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //ApplicationContext app = new ClassPathXmlApplicationContext("applicationContext.xml"); ServletContext servletContext = this.getServletContext(); //ApplicationContext app = (ApplicationContext) servletContext.getAttribute("app"); ApplicationContext app = WebApplicationContextUtils.getWebApplicationContext(servletContext); UserService userService = app.getBean(UserService.class); userService.save(); } }
4、配置web.xml文件
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" version="4.0"> <!-- 全局初始化参数--> <context-param> <param-name>contextConfigLocation</param-name> <param-value>applicationContext.xml</param-value> </context-param> <!-- 配置监听器--> <listener> <listener-class>com.ntect.listener.ContextLoaderListener</listener-class> </listener> <!-- 配置测试用的servlet--> <servlet> <servlet-name>UserServlet</servlet-name> <servlet-class>com.ntect.web.UserServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>UserServlet</servlet-name> <url-pattern>/userServlet</url-pattern> </servlet-mapping> </web-app>
5、测试
浏览器访问
http://localhost:8080/userServlet
控制台输出
上面地分析只是为了方便理解，不用手动实现，Spring提供了一个监听器ContextLoaderListener就是对上述功能的封装，该监听器内部加载Spring配置文件，创建应用上下文对象，并存储到ServletContext域中，提供了一个客户端工具WebApplicationContextUtils获取应用上下文对象。
需要做两件事：
1、在web.xml中配置ContextLoaderListener监听器（导入spring-web坐标）
2、使用WebApplicationContextUtils获得应用上下文对象ApplicationContext
<dependency> <groupId>org.springframework</groupId> <artifactId>spring-web</artifactId> <version>5.3.16</version> </dependency>
<!-- 全局初始化参数--> <context-param> <param-name>contextConfigLocation</param-name> <param-value>classpath:applicationContext.xml</param-value> </context-param> <!-- 配置监听器--> <listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener>
ApplicationContext app = WebApplicationContextUtils.getWebApplicationContext(servletContext); UserService userService = app.getBean(UserService.class);
