详解如何实现SpringBoot的底层注解

/**
 * 1、@Configuration 告诉SpringBoot这是一个配置类，相当于一个xml配置文件
 *
 * 2、配置类里面使用 @Bean 标注在方法上 来给容器注册组件，默认是单实例的
 *
 * 3、配置类本身也是一个组件
 */
@Configuration(proxyBeanMethods = true)
public class MyConfig {

    @Bean
    public User user01(){
        return new User("zhangsan",23);
    }

    @Bean
    public Pet pet01(){
        return new Pet("cat");
    }
}

/**
 * 主程序类
 * @SpringBootApplication：这是一个SpringBoot应用
 */
@SpringBootApplication
public class MainApplication {
    public static void main(String[] args) {
        //返回IOC容器
        ConfigurableApplicationContext context = SpringApplication.run(MainApplication.class, args);

        //从容器中获取bean
        User user = context.getBean(User.class);
        System.out.println(user);

        Pet pet = context.getBean("pet01", Pet.class);
        System.out.println(pet);

        MyConfig myConfig = context.getBean(MyConfig.class);
        System.out.println(myConfig);

        /*如果配置@Configuration(proxyBeanMethods = true)，代理对象调用方法从容器中拿组件，SpringBoot总会检查容器中是否有这个组件
        * 保持组件的单实例*/
        User user1 = myConfig.user01();
        User user2 = myConfig.user01();
        System.out.println(user1 == user2);

    }
}

  /*如果配置@Configuration(proxyBeanMethods = true)，代理对象调用方法从容器中拿组件，SpringBoot总会检查容器中是否有这个组件
        * 保持组件的单实例*/
        User user1 = myConfig.user01();
        User user2 = myConfig.user01();
        System.out.println(user1 == user2);		//true

public class User {
    private String name;
    private Integer age;

    private Pet pet;

    public Pet getPet() {
        return pet;
    }
}

@Configuration(proxyBeanMethods = false)
public class MyConfig {

    @Bean
    public User user01(){
        User user = new User("zhangsan", 23);
        //User组件依赖了Pet组件
        user.setPet(pet01());
        return user;
    }

    @Bean
    public Pet pet01(){
        return new Pet("cat");
    }
}

@SpringBootApplication
public class MainApplication {
    public static void main(String[] args) {
    
        User user01 = context.getBean("user01", User.class);
        Pet pet01 = context.getBean("pet01", Pet.class);
        System.out.println(user01.getPet() == pet01);		//true
        
    }
}

@Import(DBHelper.class)
@Configuration(proxyBeanMethods = false)
public class MyConfig {

}

@EnableConfigurationProperties(Pet.class)
public class MyConfig {
}

//@Component
@ConfigurationProperties(prefix = "mydog")
public class Pet {
}