1. Spring如何在WEB應用中使用？
   • spring-web-4.0.0.RELEASE.jar
   • spring-webmvc-4.0.0.RELEASE.jar
2. Spring的配置檔案，沒有什麼不同
3. 如何建立IOC容器
   • 非WEB應用在main方法中直接建立
   • 應該在WEB應用被伺服器載入時就建立IOC容器：
     • 在ServletContextListener#contextInitialized(ServletContextEvent sce) 方法中建立IOC容器。
   • 在WEB應用的其他元件中如何來訪問IOC容器呢？
     • 在ServletContextListener#contextInitialized(ServletContextEvent sce)方法中建立IOC容器後，可以把其放在ServletContext(即application域)的一個屬性中。
   • 實際上Spring配置檔案的名字和位置應該也是可配置的！將其配置到當前WEB應用的初始化引數中較為合適。

例子程式

基本結構

Person.java

package com.spring.struts2.
 
beans;

public class Person {

    private String username;

    public void setUsername(String username) {
        this.username = username;
    }
    public void hello(){
        System.out.println("My name is "+username);
    }
}

SpringServletContextListener.java

package com.spring.struts2.listeners;
 


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 SpringServletContextListener implements ServletContextListener{

    // Public constructor is required by servlet spec
    public SpringServletContextListener() {
    }

    // -------------------------------------------------------
    // ServletContextListener implementation
    // -------------------------------------------------------
    public void contextInitialized(ServletContextEvent arg0) {
        //1.獲取Spring配置檔案的名稱。
        ServletContext servletContext = arg0.getServletContext();
        String config = servletContext.getInitParameter("configLocation");

        //1.建立IOC容器
        ApplicationContext ctx = new ClassPathXmlApplicationContext(config);

        //2.把IOC容器放在ServletContext的一個屬性中
        servletContext.setAttribute("ApplicationContext",ctx);
    }

    public void contextDestroyed(ServletContextEvent sce) {
      /* This method is invoked when the Servlet Context 
         (the Web application) is undeployed or 
         Application Server shuts down.
      */
    }

}

TestServlet.java

package com.spring.struts2.servlets;

import com.spring.struts2.beans.Person;
import org.springframework.context.ApplicationContext;

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 TestServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       //1.從application域物件中得到IOC容器的利用
        ServletContext servletContext = getServletContext();
        ApplicationContext ctx = (ApplicationContext) servletContext.getAttribute("ApplicationContext");


        //2.從IOC容器中得到需要的bean
        Person person = ctx.getBean(Person.class);
        person.hello();
    }
}

applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="person"
          class="com.spring.struts2.beans.Person">
        <property name="username" value="spring"></property>
    </bean>
</beans>

web.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">


    <!--配置Spring配置檔案的名稱和位置-->
    <context-param>
        <param-name>configLocation</param-name>
        <param-value>applicationContext.xml</param-value>
    </context-param>

    <!--啟動IOC容器的ServletContextListener-->
    <listener>
        <listener-class>com.spring.struts2.listeners.SpringServletContextListener</listener-class>
    </listener>

    <servlet>
        <description></description>
        <display-name>TestServlet</display-name>
        <servlet-name>TestServlet</servlet-name>
        <servlet-class>com.spring.struts2.servlets.TestServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>TestServlet</servlet-name>
        <url-pattern>/TestServlet</url-pattern>
    </servlet-mapping>

</web-app>

index.jsp

<%--
  Created by IntelliJ IDEA.
  User: 14741
  Date: 2018/12/9
  Time: 15:24
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title>$Title$</title>
  </head>
  <body>
      <a href="${pageContext.request.contextPath}/TestServlet">TestServlet</a>
  </body>
</html>

執行結果 在頁面點選過後: