spring集成web环境-ContextLoaderListener监听分析

监听器的分析

web.xml配置文件内容

  
    contextConfigLocation
    classpath:applicationContext.xml
  


	zcf.listener.ContextLoaderListener

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监听器代码，创建spring容器并将其放到全局上下文

public class ContextLoaderListener implements ServletContextListener {
    @Override
    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最大的ServletContext域中
        servletContext.setAttribute("app",app);
        System.out.println("spring容器创建完毕");
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
    }
}
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获取Spring容器方法

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

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使用

public class UserServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
//        ApplicationContext app = WebApplicationContextUtils.getWebApplicationContext(servletContext);

        ApplicationContext app = WebApplicationContextUtils.getWebApplicationContext(servletContext);
        UserService userService = app.getBean(UserService.class);
        userService.save();
    }
}
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Spring提供获取应用上下文对象

引入坐标

    
      org.springframework
      spring-web
      5.2.6.RELEASE
    
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web.xml配置文件配置

  
    contextConfigLocation
    classpath:applicationContext.xml
  

  
    org.springframework.web.context.ContextLoaderListener
  
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使用

public class UserServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
//        ApplicationContext app = WebApplicationContextUtils.getWebApplicationContext(servletContext);

        ApplicationContext app = WebApplicationContextUtils.getWebApplicationContext(servletContext);
        UserService userService = app.getBean(UserService.class);
        userService.save();
    }
}
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