Spring 原理

Spring 使用的演变

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使用配置文件

IOC

package testDI;

// 数据层
public class UserDao {
    public void saveUser() {
        System.out.println("User saved to the database.");
    }
}

​UserService​

package testDI;

// 业务层
public class UserService {
    private UserDao userDao;

    public UserService(){
        this.userDao = new UserDao();
    }

    public void save() {
        userDao.saveUser();
    }
}

​SpringConfig.xml​

<?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 http://www.springframework.org/schema/beans/spring-beans.xsd">

    <!--
		bean标签标示配置bean
    	id属性标示给bean起名字
    	class属性表示给bean定义类型
	-->
    <bean id="userDao" class="testDI.UserDao"/>
    <bean id="userService" class="testDI.UserService"/>

</beans>

package testDI;

import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @author charmingdaidai
 * @project study
 * @since 2025/02/08 15:33
 */
// 客户端调用（使用 Spring IOC 容器）
public class Client {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("SpringConfig.xml");

        // 通过IOC容器获取UserService实例，并自动注入UserDao
        UserService userService = context.getBean(UserService.class);
        userService.save();

        context.close();
    }
}

DI

​SpringConfig.xml​

<?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 http://www.springframework.org/schema/beans/spring-beans.xsd">

    <!--
		bean标签标示配置bean
    	id属性标示给bean起名字
    	class属性表示给bean定义类型
	-->
    <bean id="userDao" class="testDI.UserDao"/>
    <bean id="userService" class="testDI.UserService">
        <!--配置server与dao的关系-->
        <!--
				property标签表示配置当前bean的属性
        		name属性表示配置哪一个具体的属性
        		ref属性表示参照哪一个bean
		-->
        <property name="userDao" ref="userDao"/>
    </bean>
</beans>

​UserService​ 中提供对应的set方法

package testDI;

// 业务层
public class UserService {
    private UserDao userDao;

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

    public void save() {
        userDao.saveUser();
    }
}

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纯注解

使用 Java类 替换 配置文件

package testDI;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

/**
 * @author charmingdaidai
 * @project study
 * @since 2025/02/08 15:39
 */

@Configuration
@ComponentScan("testDI") // 指定扫描的包路径
public class AppConfig {
    // Spring会自动将 UserDao 注入到 UserService 中
}

更改 context 的创建方式

package testDI;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

/**
 * @author charmingdaidai
 * @project study
 * @since 2025/02/08 15:33
 */
// 客户端调用（使用 Spring IOC 容器）
public class Client {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);

        // 通过IOC容器获取UserService实例，并自动注入UserDao
        UserService userService = context.getBean(UserService.class);
        userService.save();

        context.close();
    }
}

注册为 Bean

package testDI;

import org.springframework.stereotype.Component;

// 数据层
@Component
public class UserDao {
    public void saveUser() {
        System.out.println("User saved to the database.");
    }
}

package testDI;

import org.springframework.stereotype.Service;

import javax.annotation.Resource;

// 业务层
@Service
public class UserService {
    @Resource
    private UserDao userDao;

    public void save() {
        userDao.saveUser();
    }
}

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