Java控制反转 - spring webmvc

时间:2020-08-02 12:42:12   收藏:0   阅读:88

概述

本文基于示例的方式解释控制反转,再看控制反转之前,我们先看下常规控制流程,以数据库访问为例

示例并没有实际访问数据,而是基于service和dao,模拟请求数据

创建项目

注意:本实例基于Idea开发工具

常规流程

public interface UserDao {
    String getUser();
}
public class UserDaoMSSqlImpl implements UserDao {
    public String getUser() {
        return "从SQL Server查询用户";
    }
}
public class UserDaoMySqlImpl implements UserDao {
    public String getUser() {
        return "从MySQL查询用户";
    }
}
public interface UserService {
    void getUser();
}
public class UserServiceImpl implements  UserService {
    // 如果想更换数据库,这个地方需要改一下
    private UserDao  userDao = new UserDaoMSSqlImpl();

    public void getUser() {
        System.out.println(userDao.getUser());
    }
}
public class UserTest {
    public static void main(String[] args) {
        UserService userService = new UserServiceImpl();
        userService.getUser();
    }
}

从上面的例子中看到,如果想更改数据连接,必须修改代码,也就是service类中,更新dao的初始化

控制反转流程

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-webmvc</artifactId>
        <version>5.2.8.RELEASE</version>
    </dependency>
</dependencies>
<?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
        https://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="mssqlImpl" class="com.example.dao.UserDaoMSSqlImpl"></bean>
    <bean id="mysqlImpl" class="com.example.dao.UserDaoMySqlImpl"></bean>

    <bean id="userServiceImpl" class="com.example.service.UserServiceImpl">
        <!-- 更新ref:mssqlImpl或mysqlImpl,即可实现数据库切换 -->
        <property name="userDao" ref="mysqlImpl"></property>
    </bean>
</beans>
public class UserServiceImpl implements  UserService {
    private UserDao  userDao;

    public void getUser() {
        System.out.println(userDao.getUser());
    }

    // 程序被动接受入口,依赖注入就是利用set方法注入
    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }
}
public class UserTest {
    public static void main(String[] args) {
        // 获取Spring上下文对象
        ApplicationContext context = new ClassPathXmlApplicationContext("services.xml");
        UserService userService1 = (UserService)context.getBean("userServiceImpl");
        userService1.getUser();
    }
}

从上面两个示例里面看出:

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