SpringMVC —— 第八章 Spring 与 Web 环境集成

1. 基本三层架构环境的搭建

创建一个 JavaEE 工程，选择模板为 Web 应用程序，并选用 Tomcat 作为服务器

在 pom.xml 中导入需要用到的依赖包的坐标

<?xml version="1.0" encoding="UTF-8"?>
<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.gregperlinli</groupId>
    <artifactId>spring_mvc</artifactId>
    <version>1.0-SNAPSHOT</version>
    <name>spring_mvc</name>
    <packaging>war</packaging>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.target>1.8</maven.compiler.target>
        <maven.compiler.source>1.8</maven.compiler.source>
        <junit.version>5.7.1</junit.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>javax.servlet.jsp-api</artifactId>
            <version>2.3.3</version>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>$&#123;junit.version&#125;</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-engine</artifactId>
            <version>$&#123;junit.version&#125;</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>5.3.8</version>
        </dependency>
        <dependency>
            <groupId>javax.annotation</groupId>
            <artifactId>javax.annotation-api</artifactId>
            <version>1.3.2</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.20</version>
        </dependency>
        <dependency>
            <groupId>c3p0</groupId>
            <artifactId>c3p0</artifactId>
            <version>0.9.1.2</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
            <version>5.3.8</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>3.3.1</version>
            </plugin>
        </plugins>
    </build>
</project>

配置 JDBC 和数据源（连接池）

jdbc.properties

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/test
jdbc.username=root
jdbc.password=root

com.yourname.config.DataSourceConfiguration

import com.mchange.v2.c3p0.ComboPooledDataSource;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.PropertySource;
import javax.sql.DataSource;

@PropertySource("classpath:jdbc.properties") 
public class DataSourceConfiguration &#123;
    @Value("$&#123;jdbc.driver&#125;")
    private String driver;
    @Value("$&#123;jdbc.url&#125;")
    private String url;
    @Value("$&#123;jdbc.username&#125;")
    private String username;
    @Value("$&#123;jdbc.password&#125;")
    private String password;

    @Bean("dataSource")
    public DataSource getDataSource() throws Exception &#123;
        ComboPooledDataSource dataSource = new ComboPooledDataSource();
        dataSource.setDriverClass(driver);
        dataSource.setJdbcUrl(url);
        dataSource.setUser(username);
        dataSource.setPassword(password);
        return dataSource;
    &#125;
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配置 Spring 容器

com.yourname.config.SpringConfiguration

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

@Configuration
@ComponentScan("com.gregperlinli")
@Import(&#123;DataSourceConfiguration.class&#125;)
public class SpringConfiguration &#123;
  
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编写 Dao 层

com.yourname.dao.UserDao

public interface UserDao &#123;
    public void save();
&#125;

com.yourname.dao.impl.UserDaoImpl

import com.gregperlinli.dao.UserDao;
import org.springframework.stereotype.Repository;

@Repository("userDao")
public class UserDaoImpl implements UserDao &#123;
    @Override
    public void save() &#123;
        System.out.println("Save running ...");
    &#125;
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编写 Service 层

com.yourname.service.UserService

public interface UserService &#123;
    public void save();
&#125;

com.yourname.service.impl.UserServiceImpl

import com.gregperlinli.dao.UserDao;
import com.gregperlinli.service.UserService;
import org.springframework.stereotype.Service;
import javax.annotation.Resource;

@Service("userService")
public class UserServiceImpl implements UserService &#123;
    @Resource(name = "userDao")
    private UserDao userDao;

    @Override
    public void save() &#123;
        userDao.save();
    &#125;
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编写 Web 层

com.yourname.web.UserServlet

import com.gregperlinli.config.SpringConfiguration;
import com.gregperlinli.service.UserService;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
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 java.io.IOException;

@WebServlet(name = "UserServlet", value = "/userServlet")
public class UserServlet extends HttpServlet &#123;
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException &#123;
        AnnotationConfigApplicationContext app = new AnnotationConfigApplicationContext(SpringConfiguration.class);
        UserService userService = app.getBean(UserService.class);
        userService.save();
    &#125;
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2. `ApplicationContext` 应用上下文获取方式

应用上下文对象是通过 new AnnotationConfigApplicationContext（注解）方式获取的，但是每次从容器中获得 Bean 时都要编写 new AnnotationConfigApplicationContext（注解），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 应用启动的时候，就加载 Spring 的配置文件，创建应用上下文对象 **ApplicationContext**，将其储存到最大的 ServletContext 域中，这样就可以在任意位置获得应用上下文 ApplicationContext 对象了。

示例代码：

com.yourname.listener.ContextLoaderListener

import com.gregperlinli.config.SpringConfiguration;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

@WebListener()
public class ContextLoaderListener implements ServletContextListener &#123;
    @Override
    public void contextInitialized(ServletContextEvent sce) &#123;
        AnnotationConfigApplicationContext app = new AnnotationConfigApplicationContext(SpringConfiguration.class);
        // Store the Spring application context object in the ServletContext domain
        ServletContext servletContext = sce.getServletContext();
        servletContext.setAttribute("app", app);
        System.out.println("Spring container created");
    &#125;
    @Override
    public void contextDestroyed(ServletContextEvent sce) &#123;
    &#125;
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com.yourname.utils.WebApplicationContextUtils

import org.springframework.context.ApplicationContext;
import javax.servlet.ServletContext;

public class WebApplicationContextUtils &#123;
    public static ApplicationContext getWebApplicationContext(ServletContext servletContext) &#123;
        return (ApplicationContext) servletContext.getAttribute("app");
    &#125;
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com.yourname.web.userServlet

import com.gregperlinli.service.UserService;
import com.gregperlinli.utils.WebApplicationContextUtils;
import org.springframework.context.ApplicationContext;
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 java.io.IOException;

@WebServlet(name = "UserServlet", value = "/userServlet")
public class UserServlet extends HttpServlet &#123;
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException &#123;
        ServletContext servletContext = this.getServletContext();
        ApplicationContext app = WebApplicationContextUtils.getWebApplicationContext(servletContext);
        UserService userService = app.getBean(UserService.class);
        userService.save();
    &#125;
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3. Spring 提供获取应用上下文的工具

Spring 提供了要一个监听器 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。

我们只需要做两件事情

配置 ContextLoaderListener 监听器（需导入 spring-web 坐标）
使用 WebApplicationContextUtils 获得应用上下文对象 ApplicationContext

示例代码：

pom.xml

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-web</artifactId>
    <version>5.2.7.RELEASE</version>
</dependency>

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">
  
      <!-- Global initialization parameters -->
      <context-param>
          <param-name>contetConfiguration</param-name>
          <param-value>classpath:applicationContext.xml</param-value>
      </context-param>
  
      <!-- Configure listeners -->
      <listener>
              <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
      </listener>
</web-app>

com.yourname.web.userServlet

import com.gregperlinli.service.UserService;
import org.springframework.web.context.support.WebApplicationContextUtils;
import org.springframework.context.ApplicationContext;
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 java.io.IOException;

@WebServlet(name = "UserServlet", value = "/userServlet")
public class UserServlet extends HttpServlet &#123;
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException &#123;
        ServletContext servletContext = this.getServletContext();
        ApplicationContext app = WebApplicationContextUtils.getWebApplicationContext(servletContext);
        UserService userService = app.getBean(UserService.class);
        userService.save();
    &#125;
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