SpringMVC 温习笔记(一)服务器启动和组件解析-蒲公英云

spring 组件扫描解析

首先小猿先引入一张图片，该图片可以全面的诠释自定义组件的全部运行过程：
在这里插入图片描述
整个过程中最为核心的思想就是tomcat服务器启动的时候可以直接通过监听器去加载spring配置文件applicationContext.xml文件，以这种方式，我们可以借助tomcat服务器加载监听器的过程，可将service层，dao层的各类bean纳入到spring容器中来进行管理，这样就使得整个启动过程变得非常完美，总之自定义监听类的本质作用是将tomcat容器初始化和spring容器初始化紧密的链接在了一起。
下面小猿将整个小案例的代码附在下面。

项目依赖

<dependency>
       <groupId>mysql</groupId>
       <artifactId>mysql-connector-java</artifactId>
       <version>5.1.32</version>
   </dependency>
   <dependency>
       <groupId>c3p0</groupId>
       <artifactId>c3p0</artifactId>
       <version>0.9.1.2</version>
   </dependency>
   <dependency>
       <groupId>com.alibaba</groupId>
       <artifactId>druid</artifactId>
       <version>1.1.10</version>
   </dependency>
   <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>
       <version>4.12</version>
       <scope>test</scope>
   </dependency>
   <dependency>
       <groupId>commons-fileupload</groupId>
       <artifactId>commons-fileupload</artifactId>
       <version>1.3.3</version>
   </dependency>
   <dependency>
       <groupId>org.springframework</groupId>
       <artifactId>spring-context</artifactId>
       <version>5.0.5.RELEASE</version>
   </dependency>
   <dependency>
       <groupId>org.springframework</groupId>
       <artifactId>spring-test</artifactId>
       <version>5.0.5.RELEASE</version>
   </dependency>
   <dependency>
       <groupId>org.springframework</groupId>
       <artifactId>spring-web</artifactId>
       <version>5.0.5.RELEASE</version>
   </dependency>
   <dependency>
       <groupId>org.springframework</groupId>
       <artifactId>spring-webmvc</artifactId>
       <version>5.0.5.RELEASE</version>
   </dependency>
   <dependency>
       <groupId>javax.servlet</groupId>
       <artifactId>javax.servlet-api</artifactId>
       <version>3.0.1</version>
       <scope>provided</scope>
   </dependency>
   <dependency>
       <groupId>javax.servlet.jsp</groupId>
       <artifactId>javax.servlet.jsp-api</artifactId>
       <version>2.2.1</version>
       <scope>provided</scope>
   </dependency>

dao 层

接口

public interface UserDao { 
    public void save();
}

实现类

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

service层

接口

public interface UserService { 
    public void save();
}

实现类

public class UserServiceImpl implements UserService { 
    private UserDao userDao;
    public void setUserDao(UserDao userDao) { 
        this.userDao = userDao;
    }
    public void save() { 
        userDao.save();
    }
}

自定义监听类和工具类

监听类

public class  ContextLoaderListener implements ServletContextListener{ 
    public void contextInitialized(ServletContextEvent sce) { 
        ServletContext servletContext = sce.getServletContext();
        String contextConfigLocation = servletContext
                .getInitParameter("contextConfigLocation");
        ApplicationContext applicationContext = new
                ClassPathXmlApplicationContext(contextConfigLocation);
        servletContext.setAttribute("applicationContext",applicationContext);
        System.out.println("容器已经创建完毕。。。。。。");
    }
    public void contextDestroyed(ServletContextEvent sce) { 
    }
}

工具类

public class WebApplicationContextUtils { 
    public static ApplicationContext getAttribute(ServletContext servletContext){ 
        return (ApplicationContext) servletContext.getAttribute("applicationContext");
    }
}

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" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
    <!--加载外部的properties文件-->
    <context:property-placeholder location="classpath:jdbc.properties"/>
    <!--配置数据源-->
    <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
        <property name="driverClass" value="${jdbc.driver}"></property>
        <property name="jdbcUrl" value="${jdbc.url}"></property>
        <property name="user" value="${jdbc.username}"></property>
        <property name="password" value="${jdbc.password}"></property>
    </bean>
    <!--配置Dao-->
    <bean id="userDao" class="com.feitian.component.dao.impl.UserDaoImpl"></bean>
    <!--配置service-->
    <bean id="userService" class="com.feitian.component.servicce.impl.UserServiceImpl">
        <property name="userDao" ref="userDao"/>
    </bean>
</beans>

当然此处配置的数据库暂时没有用。

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">
    <!--将applicationContext.xml放入ServletContext，方便自定义监听类初始化该文件。-->
    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:applicationContext.xml</param-value>
    </context-param>
    <!--监听器启动时要加载定义监听类-->
    <listener>
        <listener-class>com.feitian.component.web.listener.ContextLoaderListener</listener-class>
    </listener>
    <!--将UserServlet加载到web容器中-->
    <servlet>
        <servlet-name>UserServlet</servlet-name>
        <servlet-class>com.feitian.component.web.servlet.UserServlet</servlet-class>
    </servlet>
    <!--映射UserServlet为userServlet-->
    <servlet-mapping>
        <servlet-name>UserServlet</servlet-name>
        <url-pattern>/userServlet</url-pattern>
    </servlet-mapping>
</web-app>

web层

public class UserServlet extends HttpServlet { 
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException { 
        ServletContext servletContext = this.getServletContext();
        ApplicationContext applicationContext =
                WebApplicationContextUtils.getAttribute(servletContext);
        UserService userService = applicationContext.getBean(UserService.class);
        userService.save();
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException { 
        this.doGet(req,resp);
    }
}