Spring中的控制反转（IOC）

前言：笔记是参考B站up主遇见狂神说，图片、代码都是哦。因为最近特别喜欢他教的课程，所以就一边跟着学习，一边在blog写笔记~（图片、代码来源狂神说Java，侵权必删！）
狂神说Java学习路线B站网站：https://www.bilibili.com/read/cv5702420

Dao层

1.UserDao 接口
2.UserDaoImpl 实现类

Service层

3.UserService 业务接口
4.UserServiceImpl 业务实现类
用户实际调用service层 不会动dao层！

Dao层接口创建

package com.ckm.dao;

public interface UserDao {
    void getUser();
}

Dao层实现类1创建

package com.ckm.dao;

public class UserDaoImpl implements UserDao{
    @Override
    public void getUser() {
        System.out.println("获取了User数据");
    }
}

Dao层实现类2创建

package com.ckm.dao;

public class UserDaoMysqlImpl implements UserDao{
    @Override
    public void getUser() {
        System.out.println("mysql使用了数据");
    }
}

Service层接口创建

package com.ckm.service;

public interface UserService {
    void getUser();
}

Service层接口实现类创建

package com.ckm.service;

import com.ckm.dao.UserDao;
import com.ckm.dao.UserDaoImpl;

public class UserServiceImpl implements UserService{

//    private UserDao userDao = new UserDaoImpl();
    //利用set进行动态实现值的注入
    private UserDao userDao;
    public void setUserDao(UserDao userDao){
        this.userDao = userDao;
    }

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

单元测试

import com.ckm.dao.UserDaoImpl;
import com.ckm.dao.UserDaoMysqlImpl;
import com.ckm.service.UserServiceImpl;

public class TestIOC {
    public static void main(String[] args) {
        //用户实际调用service层 不会动dao层！
        UserServiceImpl userService = new UserServiceImpl();
        userService.setUserDao(new UserDaoMysqlImpl());
        userService.getUser();
    }
}

resources中新建beans.xml文件

dao层、Service层代码不变
测试类

import com.ckm.service.UserServiceImpl;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class TestIOC {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        UserServiceImpl userServiceImpl = (UserServiceImpl) context.getBean("UserServiceImpl");
        userServiceImpl.getUser();
    }
}

User类

package com.ckm.pojo;

public class Hello {
    private String str;

    public String getStr() {
        return str;
    }

    public void setStr(String str) {
        this.str = str;
    }

    @Override
    public String toString() {
        return "Hello{" +
                "str='" + str + ''' +
                '}';
    }
}

beans.xml

测试类

import com.ckm.pojo.Hello;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MyTest {
    public static void main(String[] args) {
        //获取spring的上下文对象
        //xml加载必须new ClassPathXmlApplicationContext()
        ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        //我们的对象现在都在spring中管理，我们要使用，直接去里面取出来
        Hello hello = (Hello) context.getBean("hello");
        System.out.println(hello.getStr());
    }
}

当getBean的时候，这个类就已经被实例化了，就会执行无参构造方法
有参构造的User类

package com.ckm.pojo;

public class User {
    private String name;
//    public User() {
//        System.out.println("无参构造");
//    }
    public User(String name){
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
    public void show(){
        System.out.println("name="+name);
    }
}

编写Beans.xml