1、Spring如何在web应用中使用

几点说明：
1) 需要额外加入的jar包：
spring-web-4.0.0.RELEASE.jar
spring-webmvc-4.0.0.RELEASE.jar
2) Spring的配置文件，没有什么不同
3) 如何创建IOC容器？
① 非WEB应用在main方法中直接创建
② 应该在WEB应用被服务器加载时就创建IOC容器
在ServletContextListener#void contextInitialized(ServletContextEvent sce)方法中创建IOC容器
③ 在ServletContextListener#void contextInitialized(ServletContextEvent sce)方法中创建IOC容器后，可以将其放在ServletContext(即application域)的一个属性中。
④ 实际上，Spring配置文件的名字和位置应该也是可以配置的！将其配置到当前WEB应用的初始化参数中较为合适。

2、关键文件编码

① SpringServletContextListener(ServletContextListener)(核心)

package com.lty.spring.struts2.listener;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * Application Lifecycle Listener implementation class SpringServletContextListener
 *
 */
@WebListener
public class SpringServletContextListener implements ServletContextListener {

    /**
     * Default constructor. 
     */
    public SpringServletContextListener() {
    	
    }

	/**
     * @see ServletContextListener#contextDestroyed(ServletContextEvent)
     */
    public void contextDestroyed(ServletContextEvent arg0)  { 
    	
    }

	/**
     * @see ServletContextListener#contextInitialized(ServletContextEvent)
     */
    public void contextInitialized(ServletContextEvent event)  { 
    	//获取Spring配置文件的名称(全路径)
    	ServletContext servletContext = event.getServletContext();
    	String config = servletContext.getInitParameter("configLocation");
    	
    	//1、创建IOC容器
    	ApplicationContext ctx = new ClassPathXmlApplicationContext(config);
    	
    	//2、将IOC容器放在ServletContext的一个属性中
    	servletContext.setAttribute("applicationContext", ctx);
    }
	
}

② TestServlet(Servlet)

package com.lty.spring.struts2.servlet;

import java.io.IOException;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.context.ApplicationContext;

import com.lty.spring.struts2.bean.Person;

/**
 * Servlet implementation class TestServlet
 */
@WebServlet("/TestServlet")
public class TestServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//1、从application域对象中获取IOC容器的引用
		ServletContext servletContext = getServletContext();
		ApplicationContext ctx = (ApplicationContext) servletContext.getAttribute("applicationContext");
		
		//2、从IOC容器中得到需要的bean
		Person person = ctx.getBean(Person.class);
		person.hello();
	}

}

③ web.xml(核心)

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns="http://java.sun.com/xml/ns/javaee"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
	id="WebApp_ID" version="2.5">
	
	<!-- 配置Spring配置文件的名称和位置 -->
	<context-param>
		<param-name>configLocation</param-name>
		<param-value>applicationContext.xml</param-value>
		
		<!-- 默认类路径下 -->
		<!-- <param-value>classpath:com/lty/spring/struts2/servlet/beans.xml</param-value> -->
	</context-param>
	
	<!-- 启动IOC容器的ServletContextListener -->
	<listener>
		<listener-class>com.lty.spring.struts2.listener.SpringServletContextListener</listener-class>
	</listener>
</web-app>