【Java】IoC注入的三种方式

1、根据类型注入

@Controller
public class UserController {
    public void sayHi(){
        System.out.println("Hi,controller");
    }
}

@SpringBootApplication
public class IocSpringApplication {

    public static void main(String[] args) {
        ApplicationContext context = SpringApplication.run(IocSpringApplication.class, args);

        UserController controller = context.getBean(UserController.class);
        controller.sayHi();
    }

}

根据类型注入时，不适合一个类型有多个bean(多个对象)的情况

2、根据名称注入

@Service
public class UserService {
    public void sayHi(){
        System.out.println("Hi,service");
    }
}

@SpringBootApplication
public class IocSpringApplication {

    public static void main(String[] args) {
        ApplicationContext context = SpringApplication.run(IocSpringApplication.class, args);

        UserService service = (UserService) context.getBean("userService");
        service.sayHi();
    }

}

根据名称注入时，要做强转，否则报错

 3、根据名称和类型注入

@Component
public class UserComponent {
    public void sayHi(){
        System.out.println("Hi,component");
    }
}

@SpringBootApplication
public class IocSpringApplication {

    public static void main(String[] args) {
        ApplicationContext context = SpringApplication.run(IocSpringApplication.class, args);

        UserComponent component = context.getBean("userComponent", UserComponent.class);
        component.sayHi();
    }

}

根据类型和名称注入时，不用做强转

4、bean的名字

（1）重命名

 @Controller，@Service，@Component，@Configuration，@Repository 等注解后面都可以重新命名

@Component("component")
public class UserComponent {
    public void sayHi(){
        System.out.println("Hi,component");
    }
}

@SpringBootApplication
public class IocSpringApplication {
    public static void main(String[] args) {
        ApplicationContext context = SpringApplication.run(IocSpringApplication.class, args);

        UserComponent component = context.getBean("component", UserComponent.class);
        component.sayHi();
    }

}

（2）未命名

⭐未指定名称时，Spring指定的名称

✅类名首字母小写，小驼峰——如：UserController转为userController

✅当类名前两个字母为大写时，直接返回原名称——如：USerController不变，直接返回USerController