Java Spring IOC 使用new、构造器、set、xml三种方式推导实现

DAO接口

package com.IOC.dao;

public interface IUserDao {
    void get();
}

两个DAO接口实现类

package com.IOC.dao;

public class UserDaoMysqlImpl implements IUserDao {

    @Override
    public void get() {
        System.out.println("Mysql 获取User");
    }
}

package com.IOC.dao;

public class UserDaoOracleImpl implements IUserDao {

    @Override
    public void get() {
        System.out.println("Oracle 获取User");
    }
}

service接口

package com.IOC.service;

public interface IUserService {
    void get();
}

第1种写法

*** 普通的三层切换多个dao，只能去修改service中的new对象 【耦合性太高】**

package com.IOC.service;

import com.IOC.dao.IUserDao;
import com.IOC.dao.UserDaoMysqlImpl;
import com.IOC.dao.UserDaoOracleImpl;

public class UserServiceImpl implements IUserService {
    //new mysql底层
    private IUserDao userDaoMysql = new UserDaoMysqlImpl();
    //new orcle底层
    private IUserDao userDaoOracle = new UserDaoOracleImpl();

    @Override
    public void get() {
        //调用mysql底层方法
        userDaoMysql.get();
        //调用orcle底层方法
        userDaoOracle.get();
    }
}

第2种写法

*** 利用set进行动态注入**

package com.IOC.service;

import com.IOC.dao.IUserDao;

public class UserServiceImplSet implements IUserService {
    private IUserDao userDao;

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

    @Override
    public void get() {
        userDao.get();
    }
}

第3种写法

*** 使用构造器进行动态注入**

package com.IOC.service;

import com.IOC.dao.IUserDao;

public class UserServiceImplContructor implements IUserService {
    /**
     * 第三种写法
     * 使用构造器进行动态注入
     */
    private IUserDao iUserDao;

    public UserServiceImplContructor(IUserDao iUserDao) {
        this.iUserDao = iUserDao;
    }

    @Override
    public void get() {
        iUserDao.get();
    }
}

第4种写法xml配置

*** 利用set和xml注入**

<?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="UserDaoMysqlImpl" class="com.IOC.dao.UserDaoMysqlImpl"/>
    <bean id="UserDaoOracleImpl" class="com.IOC.dao.UserDaoOracleImpl"/>

    <bean id="UserServiceImplSet" class="com.IOC.service.UserServiceImplSet">
        <!--ref：引用spring容器中创建好的对象-->
        <property name="userDao" ref="UserDaoMysqlImpl"></property>
    </bean>
</beans>

4种方法测试类

package com.IOC;

import com.IOC.dao.UserDaoMysqlImpl;
import com.IOC.dao.UserDaoOracleImpl;
import com.IOC.service.IUserService;
import com.IOC.service.UserServiceImpl;
import com.IOC.service.UserServiceImplContructor;
import com.IOC.service.UserServiceImplSet;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class TestIOC {
    /**
     * 第1种做法
     * 普通的三层切换多个dao，只能去修改service中的new对象 【不合理】
     */
    @Test
    public void test() {
        IUserService userService = new UserServiceImpl();
        userService.get();
    }

    /**
     * 第2种写法
     * 使用set进行动态注入
     */
    @Test
    public void test2() {
        IUserService userService = new UserServiceImplSet();
        //Mysql方法注入
        ((UserServiceImplSet) userService).setUserDao(new UserDaoMysqlImpl());
        userService.get();
        //Oracle方法注入
        ((UserServiceImplSet) userService).setUserDao(new UserDaoOracleImpl());
        userService.get();

        //另一种写法,耦合性比较高，实现类变了，要改比较多地方
        UserServiceImplSet userServiceImplSet = new UserServiceImplSet();
        //Mysql方法注入
        userServiceImplSet.setUserDao(new UserDaoMysqlImpl());
        userServiceImplSet.get();
        //Oracle方法注入
        userServiceImplSet.setUserDao(new UserDaoOracleImpl());
        userServiceImplSet.get();
    }

    /**
     * 第3种写法
     * 使用构造器进行动态注入
     */
    @Test
    public void test3() {
        //Mysql方法注入
        IUserService userServiceMysql = new UserServiceImplContructor(new UserDaoMysqlImpl());
        ((UserServiceImplContructor) userServiceMysql).get();
        //Oracle方法注入
        IUserService userServiceOracle = new UserServiceImplContructor(new UserDaoOracleImpl());
        ((UserServiceImplContructor) userServiceOracle).get();
    }

    /**
     * 第4种写法
     * 使用XML配置(只能通过set实现注入，不能通过构造器)
     */
    @Test
    public void test4() {
        //获取spring上下文对象
        ApplicationContext context = new ClassPathXmlApplicationContext("IOC.xml");
        //对象都在spring上下文对象里，要用时直接取
        UserServiceImplSet bean = context.getBean(UserServiceImplSet.class);
        bean.get();
    }
}