Spring集成web环境（手动实现）

1.创建UserDao接口及其实现类UserDaoImpl（接口代码省略)

public class UserDaoImpl implements UserDao {
    @Override
    public void save() {
        System.out.println("save running....");
    }
}

2.创建UserService及其实现类UserDaoImpl（接口代码省略）

public class UserServiceImpl implements UserService {

    private UserDao userDao;

    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }

    @Override
    public void save1() {
        userDao.save();
    }
}

3.将UserDaoImpl及其UserServiceImpl注入到spring容器当中

<?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">

<!--    配置Dao-->
    <bean id="userDao" class="com.hao.dao.impl.UserDaoImpl"/>

<!--    配置Service-->
    <bean id="userService" class="com.hao.service.impl.UserServiceImpl">
        <property name="userDao" ref="userDao"/>
    </bean>

</beans>

4.编写UserServlet

public class UserServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) {
        ApplicationContext context=new ClassPathXmlApplicationContext("applicationContext.xml");
        UserService service = context.getBean(UserService.class);
        service.save1();
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

5.配置web.xml

<?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_3_0.xsd"
         id="WebApp_ID" version="3.0">
   
    <servlet>
        <servlet-name>UserServlet</servlet-name>
        <servlet-class>com.hao.web.UserServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>UserServlet</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
</web-app>

6.启动tomcat服务器，在浏览器访问userServlet

---

我们思考这一段代码

public class UserServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) {
        ApplicationContext context=new ClassPathXmlApplicationContext("applicationContext.xml");
        UserService service = context.getBean(UserService.class);
        service.save1();
    }

当我们每次访问userServlet时，是不是都会创建一个spring容器，这样是不是造成了很大地问题，还有一个问题就是我们在用户访问userServlet时才创建spring容器，是不是会造成效率底下地问题，所以引入了监听器的概念，我们使用了范围最大的ServletContextListener监听器（用来监听ServletContext，ServletContext对象在服务器启动时就会创建，在初始化方法时就创建spring容器，提供访问效率；

创建普通类，让它实现ServletContextListener接口

public class ContextLoaderListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        ApplicationContext context=new ClassPathXmlApplicationContext("applicationContext.xml");

        //将spring应用上下文对象存储到ServletContext域中
        ServletContext servletContext = servletContextEvent.getServletContext();
        servletContext.setAttribute("app",context);
        System.out.println("spring容器创建完毕!");
    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {

    }
}

在web.xml中配置监听器

 <listener>
        <listener-class>com.hao.listener.ContextLoaderListener</listener-class>
    </listener>

修改UserServlet类里面的代码

public class UserServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) {
        ServletContext servletContext = this.getServletContext();
        ApplicationContext app = (ApplicationContext) servletContext.getAttribute("app");
        UserService userService = app.getBean(UserService.class);
        userService.save1();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

然后启动服务器，访问userServlet（spring容器的创建在服务器启动时就会创建
结果：