Java 中的控制反转(IOC)详解

package com.ckm.dao;
public interface UserDao {
    void getUser();
}

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

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

package com.ckm.service;
public interface UserService {
    void getUser();
}

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();
    }
}

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();
    }
}

<?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">
    <!--使用Spring来创建对象，在Spring这些都称为Bean-->
    <!--bean = 对象-->
    <!--id = 变量名-->
    <!--class = new的对象-->
    <!--property 相当于给对象中的属性设值-->
    <bean id="DaoImpl" class="com.ckm.dao.UserDaoImpl" />
    <bean id="MysqlImpl" class="com.ckm.dao.UserDaoMysqlImpl" />
    <bean id="UserServiceImpl" class="com.ckm.service.UserServiceImpl">
        <!--
        value具体的值，基本数据类型
        ref是引用Spring中创建好的对象
        用户需要什么 就直接修改ref就ok
        -->
        <property name="userDao" ref="MysqlImpl" />
    </bean>
</beans>

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();
    }
}

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 + '\'' +
                '}';
    }
}

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 + '\'' +
                '}';
    }
}

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());
    }
}

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);
    }
}

    <!--第一种 下标赋值-->
    <bean id="user" class="com.ckm.pojo.User">
        <constructor-arg index="0" value="这个是第一种有参设置的name"/>
    </bean>

    <!--第二种 直接通过参数名-->
    <bean id="user" class="com.ckm.pojo.User">
        <constructor-arg name="name" value="这个是第二种方法是有参设置的name"/>
    </bean>

    <!--alias是别名，我们可以使用这个别名来获取这个对象-->
    <alias name="user" alias="userNew"/>

    <!--在bean中name也是别名，可以同时取多个别名-->
    <bean id="user" class="com.ckm.pojo.User" name="user1,user2,user3,user4"/>

   <!--这个import，一般用于团队开发，他可以将多个配置文件导入合并成一个-->
    <import resource="beans1.xml"/>
    <import resource="beans2.xml"/>