Spring快速入门——Spring集成Web环境

基本三层架构环境搭建

• pom.xml

  
  <project xmlns="http://maven.apache.org/POM/4.0.0"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
      <modelVersion>4.0.0modelVersion>
  
      <groupId>org.examplegroupId>
      <artifactId>spring_mvcartifactId>
      <version>1.0-SNAPSHOTversion>
      <packaging>warpackaging>
      <dependencies>
          <dependency>
              <groupId>org.springframeworkgroupId>
              <artifactId>spring-contextartifactId>
              <version>5.3.16version>
          dependency>
          <dependency>
              <groupId>org.springframeworkgroupId>
              <artifactId>spring-testartifactId>
              <version>5.3.16version>
          dependency>
          <dependency>
              <groupId>junitgroupId>
              <artifactId>junitartifactId>
              <version>4.12version>
              <scope>testscope>
          dependency>
          <dependency>
              <groupId>mysqlgroupId>
              <artifactId>mysql-connector-javaartifactId>
              <version>8.0.17version>
          dependency>
          <dependency>
              <groupId>c3p0groupId>
              <artifactId>c3p0artifactId>
              <version>0.9.1.2version>
          dependency>
          <dependency>
              <groupId>com.alibabagroupId>
              <artifactId>druidartifactId>
              <version>1.2.8version>
          dependency>
          <dependency>
              <groupId>javax.servletgroupId>
              <artifactId>javax.servlet-apiartifactId>
              <version>4.0.1version>
          dependency>
          <dependency>
              <groupId>javax.servlet.jspgroupId>
              <artifactId>javax.servlet.jsp-apiartifactId>
              <version>2.3.3version>
          dependency>
      dependencies>
  project>
  

• applicationContext.xml配置文件

  
  <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="userDao" class="com.study.dao.impl.UserDaoImpl"/>
      
      <bean id="userService" class="com.study.service.impl.UserServiceImpl">
          <property name="userDao" ref="userDao"/>
      bean>
  beans>
  

• dao层

  package com.study.dao;
  
  public interface UserDao {
      public void save();
  }
  

  package com.study.dao.impl;
  
  import com.study.dao.UserDao;
  
  /**
   * @title: UserDaoImpl
   * @Author Mj
   * @Date: 2022/3/2 14:09
   * @Version 1.0
   */
  
  public class UserDaoImpl implements UserDao {
      public void save() {
          System.out.println("userDao save running...");
      }
  }
  

• service层

  package com.study.service;
  
  public interface UserService {
      public void save();
  }
  

  package com.study.service.impl;
  
  import com.study.dao.UserDao;
  import com.study.service.UserService;
  
  /**
   * @title: UserServiceImpl
   * @Author Mj
   * @Date: 2022/3/2 14:12
   * @Version 1.0
   */
  
  public class UserServiceImpl implements UserService {
  
      private UserDao userDao;
  
      public void setUserDao(UserDao userDao) {
          this.userDao = userDao;
      }
  
      public void save() {
          userDao.save();
      }
  }
  

• web层

  package com.study.web;
  
  import com.study.service.UserService;
  import org.springframework.context.ApplicationContext;
  import org.springframework.context.support.ClassPathXmlApplicationContext;
  
  import javax.servlet.ServletException;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import java.io.IOException;
  
  /**
   * @title: UserServlet
   * @Author Mj
   * @Date: 2022/3/2 22:08
   * @Version 1.0
   */
  public class UserServlet extends HttpServlet {
      @Override
      protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          //加载配置文件，创建Spring容器
          ApplicationContext app = new ClassPathXmlApplicationContext("applicationContext.xml");
          UserService userService = app.getBean(UserService.class);
          userService.save();
      }
  }
  

• web.xml

  
  <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">
      <servlet>
          <servlet-name>UserServletservlet-name>
          <servlet-class>com.study.web.UserServletservlet-class>
      servlet>
      <servlet-mapping>
          <servlet-name>UserServletservlet-name>
          <url-pattern>/userServleturl-pattern>
      servlet-mapping>
  web-app>
  

部署在Tomcat服务器运行，访问localhost:8080/userServlet

ApplicationContext应用上下文获取方式

• 应用上下文对象是new ClassPathXmlApplicationContext(spring配置文件)方式获取的，但是每次从容器中获得Bean时都要编写new ClassPathXMLApplicationContext(spring配置文件)，这样的弊端是配置文件加载多次，应用上下文对象创建多次。

• 在Web项目中，可以使用ServletContextListener监听Web应用的启动，我们可以在Web应用启动时，就加载Spring的配置文件，创建应用上下文对象ApplicationContext，再将其存储到最大的域servletContext域中，这样就可以在任意位置从域中获得应用上下文ApplicationContext对象了

  • web.xml文件中添加以下配置

    
    <context-param>
        <param-name>contextConfigLocationparam-name>
        <param-value>applicationContext.xmlparam-value>
    context-param>
    
    <listener>
        <listener-class>com.study.listener.ContextLoaderListenerlistener-class>
    listener>
    

  • 在ContextLoaderListener.java监听Web应用的启动

    package com.study.listener;
    
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    
    import javax.servlet.ServletContext;
    import javax.servlet.ServletContextEvent;
    import javax.servlet.ServletContextListener;
    
    /**
     * @title: ContextLoaderListener
     * @Author Mj
     * @Date: 2022/3/2 23:28
     * @Version 1.0
     */
    public class ContextLoaderListener implements ServletContextListener {
        public void contextInitialized(ServletContextEvent sce) {
            //获取servletContext对象
            ServletContext servletContext = sce.getServletContext();
    
            //通过配置文件的方式创建容器
            // ApplicationContext app = new ClassPathXmlApplicationContext("applicationContext.xml");
    
            //将配置文件放到web.xml中，从读取web.xml中的全局参数
            String contextConfigLocation = servletContext.getInitParameter("contextConfigLocation");
            ApplicationContext app = new ClassPathXmlApplicationContext(contextConfigLocation);
    
            //将Spring的应用上下文对象存储到ServletContext域中
            servletContext.setAttribute("app",app);
    
            System.err.println("spring容器创建完毕...");
            System.err.println("监听器执行完毕...");
        }
    
        public void contextDestroyed(ServletContextEvent sce) {
    
        }
    }
    

  • 编写工具类WebApplicationContextUtils类，返回从servletContext域获取的应用上下文ApplicationContext对象

    package com.study.utils;
    
    import org.springframework.context.ApplicationContext;
    
    import javax.servlet.ServletContext;
    
    /**
     * @title: WebApplicationContextUtils
     * @Author Mj
     * @Date: 2022/3/2 23:45
     * @Version 1.0
     */
    public class WebApplicationContextUtils {
        public static ApplicationContext getApplicationContext(ServletContext servletContext){
             return (ApplicationContext) servletContext.getAttribute("app");
        }
    }
    

  • 在UserServlet.java中通过WebApplicationContextUtils类的getApplicationContext()方法获取应用上下文ApplicationContext对象

    package com.study.web;
    
    import com.study.service.UserService;
    import com.study.utils.WebApplicationContextUtils;
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    
    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;
    
    /**
     * @title: UserServlet
     * @Author Mj
     * @Date: 2022/3/2 22:08
     * @Version 1.0
     */
    public class UserServlet extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            //加载配置文件，创建Spring容器
            // ApplicationContext app = new ClassPathXmlApplicationContext("applicationContext.xml");
    
            ServletContext servletContext = req.getServletContext();
    
            // ApplicationContext app = (ApplicationContext) servletContext.getAttribute("app");
            ApplicationContext app = WebApplicationContextUtils.getApplicationContext(servletContext);
            UserService userService = app.getBean(UserService.class);
            userService.save();
        }
    }
    

Spring提供获取应用上下文的工具

上面的分析不用手动实现，Spring提供了一个监听器ContextLoaderListener就是对上述功能的封装，该监听器内部加载Spring配置文件，创建应用上下文对象，并存储到ServletContext域中，提供了一个客户端工具WebApplicationContextUtils供使用者获得应用上下文对象

所以我们只需要做两件事：

1. 在web.xml中配置ContextLoaderListener监听器（导入spring-web坐标）

   
   <dependency>
       <groupId>org.springframeworkgroupId>
       <artifactId>spring-webartifactId>
       <version>5.3.16version>
   dependency>
   

   
   <listener>
       <listener-class>org.springframework.web.context.ContextLoaderListenerlistener-class>
   listener>
   

2. 使用WebApplicationContextUtils获得应用上下文对象ApplicationContext

   WebApplicationContext app = WebApplicationContextUtils.getWebApplicationContext(servletContext);
   

知识要点总结

Spring集成Web环境步骤

1. 配置ContextLoaderListener监听器
2. 使用WebApplicationContextUtils获得应用上下文