Spring 集成web环境

前文：Spring提供了一个监听器ContextLoaderListener，该监听器内部加载spring配置文件，创建上下文对象，并存储到ServletContext域中，提供了一个客户端工具WebApplicationContextUtils供使用者获得应用上下文对象。就可以使得spring配置文件applicationContet.xml在teomcat中只需要实例化一次，就可以全局调用。避免了每次getBean()都要new一个ApplicatinContext。

结构：

1.导入spring-web坐标

      org.springframework
      spring-web
      5.0.5.RELEASE

2.在web资源文件web.xml中配置spring容器的监听器ContextLoaderListener

  
  
    org.springframework.web.context.ContextLoaderListener
  

3.在web.xml中设置全局参数，告诉监听器ContextLoaderListener要加载的配置文件的名称路径

  
  
    contextConfigLocation
    classpath:applicationContext.xml
  

 注意标签的值为类加载路径，classpath:

web.xml:

  
  
    contextConfigLocation
    classpath:applicationContext.xml
  

  
  
    org.springframework.web.context.ContextLoaderListener
  


  UseServlet
  com.web.UseServlet

  
    UseServlet
    /useServlet
  

4.UseServlet

public class UseServlet extends HttpServlet {

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

手动设置监听器是配置文件在tomcat在加载时就创建在ServletContext域中，这个域很大。 

public class ContextLoadListener implements ServletContextListener {
    
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        ApplicationContext app=new ClassPathXmlApplicationContext("");
        ServletContext servletContext = servletContextEvent.getServletContext();
        servletContext.setAttribute("app",app);
        System.out.println("初始化创建完毕...");
    }

    public void contextDestroyed(ServletContextEvent servletContextEvent) {

    }
}
public class UseServlet extends HttpServlet {

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