1.1 ApplicationContext应用上下文获取方式

1）创建ContextLoaderListener实现ServletContextListener监听器

import com.itheima.service.UserService;
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 servletContextEvent) {
        
        //获取上下文对象ServletContext
        ServletContext servletContext = servletContextEvent.getServletContext();
        //获取全局初始化参数，Spring配置文件的位置
        String contextConfigLocation = servletContext.getInitParameter("contextConfigLocation");

        ApplicationContext app = new ClassPathXmlApplicationContext(contextConfigLocation);

        servletContext.setAttribute("app",app);
        System.out.println("spring容器创建完成....");
    }

    public void contextDestroyed(ServletContextEvent servletContextEvent) {

    }
}

2、创建WebApplicationContextUtils工具类

import org.springframework.context.ApplicationContext;

import javax.servlet.ServletContext;

public class WebApplicationContextUtils {

    public static ApplicationContext getWebApplicationContext(ServletContext servletContext){
        
        return (ApplicationContext) servletContext.getAttribute("app");

    }

}

3、在Web.xml中配置监听器以及全局初始化参数

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">


    <!--全局初始化参数-->
    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:applicationContext.xml</param-value>
    </context-param>
    <!-- 配置自定义的监听器 -->
    <listener>
        <listener-class>com.gmw.listener.ContextLoaderListener</listener-class>
    </listener>


    <servlet>
        <servlet-name>UserServlet</servlet-name>
        <servlet-class>com.itheima.web.UserServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>UserServlet</servlet-name>
        <url-pattern>/userServlet</url-pattern>
    </servlet-mapping>

</web-app>

4、测试

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();
    }
}

1.2 Spring提供获取应用上下文的工具

所以我们需要做的只有两件事：

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

1.3 导入Spring集成web的坐标

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-web</artifactId>
    <version>5.0.5.RELEASE</version>
</dependency>

1.4 配置ContextLoaderListener监听器

<!--全局参数-->
<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:applicationContext.xml</param-value>
</context-param>

<!--Spring的监听器-->
<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

1.5 通过工具获得应用上下文对象

ServletContext servletContext = this.getServletContext();

//获取应用上下文
ApplicationContext applicationContext = 
WebApplicationContextUtils.getWebApplicationContext(servletContext);

Object obj = applicationContext.getBean("id");