spring集成web环境的实现原理

方式:通过listener监听器来监听，在webapp启动时加载application.xml（spring的xml文件），

在spring框架中提供了相应的监听器不需要使用者写，小编自定义模仿了一下，核心就是将加载的配置文件存放在最大的域对象之中，需要时利用对应的封装工具类加载得到对应的spring容器，在从容器中取出对应的Bean对象！

首先时配置对应的xml

<?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">
    <!--lister集成spring-->
<!--<context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:spring.xml</param-value>
    </context-param>
<listener>
    <listener-class>com.atchengdu.lisenter.Contextloderlisten</listener-class>
</listener>-->
    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:spring.xml</param-value>
    </context-param>
    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>
    <servlet>
        <servlet-name>Usersevlet</servlet-name>
        <servlet-class>com.atchengdu.web.Usersevlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>Usersevlet</servlet-name>
        <url-pattern>/user</url-pattern>
    </servlet-mapping>

</web-app>

简单的写出监听器(加载xml文件配置的spring文件)

package com.atchengdu.lisenter;

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 Contextloderlisten implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        ServletContext servletContext = servletContextEvent.getServletContext();
        String contextConfigLocation = servletContext.getInitParameter("contextConfigLocation");
        //将spring存储到最大的域中
        ApplicationContext context=new ClassPathXmlApplicationContext(contextConfigLocation);
       servletContext.setAttribute("apploder",context);
    }
    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {

    }
}

最后web层获得对应的容器和对象，调用方法

package com.atchengdu.web;

import com.atchengdu.service.Userservice;
import org.springframework.context.ApplicationContext;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

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 Usersevlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext servletContext =req.getServletContext();
        ApplicationContext context = WebApplicationContextUtils.getWebApplicationContext(servletContext);
        Userservice userservice = context.getBean(Userservice.class);
        userservice.user();
    }
}
//小编的代码是写死的，，没有对获得spring容器的代码进行封装，而且更改配置文件的时候，listener监听器也要做相应的修改，主要的模仿一下实现的原理，spring提供的监听器可以不做任何修改读多个配置文件，通过封装的工具类拿到相应的容器