（1）創建一個接口

package com.min.dao;

public interface UserDao {

    public void save(String uname, String pwd);
    
}

（2）創建一個實現類將用戶信息保存到mysql數據庫中

package com.min.dao.impl;

import com.min.dao.UserDao;

public class UserDaoMysqlImpl implements UserDao {

    @Override
    public void save(String uname, String pwd) {
        System.out.println("----------UserDaoMysqlImpl----------------");
    }

}

（3）創建一個實現類將用戶信息保存到oracle數據庫中

package com.min.dao.impl;

import com.min.dao.UserDao;

public class UserDaoOracleImpl implements UserDao{

    @Override
    public void save(String uname, String pwd) {
        System.out.println("----------UserDaoOracleImpl----------------");
    }

}

（4）創建一個管理類，將接口對象作為其屬性

package com.min.manager;

import com.min.dao.UserDao;

public class UserManager {

    private UserDao userDao;　　／／將接口對象作為屬性
    
    public void save (String uname, String pwd) {
        userDao.save(uname, pwd);
    }

    public UserDao getUserDao() {
        return userDao;
    }

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

（5）在Spring配置文件applicationContext.xml將javaBean由Spring管理 

<?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:p="http://www.springframework.org/schema/p"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
    http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.1.xsd
    http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsd
    http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd">
    <bean id="hellword" class="com.min.Hellword">
    <property name="message" value="heel"></property>
    </bean>
    <bean id="mysqlimpl" class="com.min.dao.impl.UserDaoMysqlImpl"></bean>
    <bean id="oracleimpl" class="com.min.dao.impl.UserDaoOracleImpl"></bean>
　　 <!-- manager的userDao屬性依賴注入Spring來注入，可以在程序中無需修改代碼，就可以注入不同實例，本例中向mysql保存數據就注入mysqlimpl，如果后來向Oracle中保存數據只需修改注入實例-->
    <bean id="usermanager" class="com.min.manager.UserManager">
        <property name="userDao" ref="mysqlimpl"></property>
    </bean>

</beans>

（6）編寫測試類

package com.min.test;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.min.manager.UserManager;

public class Test {

    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        UserManager manager = (UserManager)context.getBean("usermanager");
        manager.save("user", "pwd ");
    }
}

執行結果

四月 21, 2019 10:46:19 上午 org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5f4da5c3: startup date ; root of context hierarchy
四月 21, 2019 10:46:19 上午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [applicationContext.xml]
----------UserDaoMysqlImpl----------------pwd