• IoC和DI

    Spring 是包含众多工具的 IoC 容器,存的是对象,对象这个词在 Spring 的范围内,称之为 bean

    IoC 是控制反转

    控制权进行了反转,比如对某一个东西的控制权在 A 手上,结果变成了 B ,Spring 管理的是 bean ,所以这里的控制权指的是 bean 的控制权,也就是对象的控制权进行了反转

    之前我们依赖的一些对象,我们需要自己去创建,通过 new 来进行创建,有了 Spring 之后我们就不再进行创建了,而是由 Spring 帮助我们进行创建,这就叫控制反转

    控制反转的一个优点主要是解耦

    耦合度高就说明两个事务的关联性密切,我们项目开发软件设计的原则是高内聚,低耦合

    高内聚 : 是指一个模块内部的关系(比如一个班级)

    低耦合 : 是指各个模块之间的关系(比如各个班级)

    高内聚低耦合就是,一个班级内需要团结协作,但是各个班级之间的相互影响要小,一个班级的问题对别的班级的影响要降低

    Spring MVC 和 Spring Boot 都属于 Spring ,Spring MVC 是基于 Spring 的一个 MVC 框架 ,而 Spring Boot 是基于 Spring 的一套快速开发整合包

    IoC 是思想, DI(依赖注入) 是是一种实现方式

    IoC 就是依赖的象的创建的控制权交给了 Spring 进行管理(存对象), DI 就是如何将依赖对象取出来,并赋给该对象的属性(取对象)

    IoC 提供了两类注解 : 

    1.类注解 : @Controller(控制器存储) , @Service(服务存储) , @Repository(仓库存储) , @Component(组件存储) , @Configuration(配置存储)

    2.方法注解 : @Bean

    接下来我们使用一下这些注解

    ①  @Controller

    先创建一个 controller 包,在里面创建一个 UserController 类,用 @Controller 告诉 Spring 帮我们管理这个对象

    1. package com.example.ioc.controller;
    2.  
    3. import org.springframework.stereotype.Controller;
    4.  
    5. //用 @Controller 告诉 Spring 帮我们管理这个对象
    6. @Controller
    7. public class UserController {
    8.     public void doController(){
    9.         System.out.println("do Controller...");
    10.     }
    11. }

    然后在启动类 DemoApplication 中查看 Spring 有没有把上面这个 Controller 存进来呢

    1. package com.example.ioc;
    2. import com.example.ioc.controller.UserController;
    3. import org.springframework.boot.SpringApplication;
    4. import org.springframework.boot.autoconfigure.SpringBootApplication;
    5. import org.springframework.context.ApplicationContext;
    6.  
    7. @SpringBootApplication
    8. public class DemoApplication {
    9.  
    10.     public static void main(String[] args) {
    11.         //Spring 上下文
    12.         ApplicationContext context = SpringApplication.run(DemoApplication.class, args);
    13.         //返回的就是 Spring 的运行环境
    14.  
    15.         UserController bean = context.getBean(UserController.class);
    16.         bean.doController();
    17.     }
    18.  
    19. }

     运行出来了,说明存进去了

     

    bean 一般使用这三个方法

    ②  @Service

    1. package com.example.ioc.service;
    2.  
    3. import org.springframework.stereotype.Service;
    4.  
    5. @Service
    6. public class UserService {
    7.     public void doService(){
    8.         System.out.println("do service....");
    9.     }
    10. }

    依旧在启动类 DemoApplication 中查看

    1. package com.example.ioc;
    2.  
    3. import com.example.ioc.controller.UserController;
    4. import com.example.ioc.service.UserService;
    5. import org.springframework.boot.SpringApplication;
    6. import org.springframework.boot.autoconfigure.SpringBootApplication;
    7. import org.springframework.context.ApplicationContext;
    8.  
    9. @SpringBootApplication
    10. public class DemoApplication {
    11.  
    12.     public static void main(String[] args) {
    13.         //Spring 上下文
    14.         ApplicationContext context = SpringApplication.run(DemoApplication.class, args);
    15.         //返回的就是 Spring 的运行环境
    16.  
    17.         UserController bean = context.getBean(UserController.class);
    18.         bean.doController();
    19.  
    20.         UserService userService = context.getBean(UserService.class);
    21.         userService.doService();
    22.     }
    23.  
    24. }

    成功拿到 

    根据名称来获取 UserService 的 bean

    (名称为类名转换为小驼峰,特殊情况就是如果类名前两位都是大写,那么bean的名称就是类名)

    1. package com.example.ioc;
    2.  
    3. import com.example.ioc.controller.UserController;
    4. import com.example.ioc.service.UserService;
    5. import org.springframework.boot.SpringApplication;
    6. import org.springframework.boot.autoconfigure.SpringBootApplication;
    7. import org.springframework.context.ApplicationContext;
    8.  
    9. @SpringBootApplication
    10. public class DemoApplication {
    11.  
    12.     public static void main(String[] args) {
    13.         //Spring 上下文
    14.         ApplicationContext context = SpringApplication.run(DemoApplication.class, args);
    15.         //返回的就是 Spring 的运行环境
    16.  
    17.         UserController bean = context.getBean(UserController.class);
    18.         bean.doController();
    19.  
    20.         UserService userService = context.getBean(UserService.class);
    21.         userService.doService();
    22.  
    23.         //根据名称来获取bean
    24.         UserService userService1 = (UserService) context.getBean("userService");
    25.         userService1.doService();
    26.     }

    根据名称+类型来拿 bean

    1. package com.example.ioc;
    2.  
    3. import com.example.ioc.controller.UserController;
    4. import com.example.ioc.service.UserService;
    5. import org.springframework.boot.SpringApplication;
    6. import org.springframework.boot.autoconfigure.SpringBootApplication;
    7. import org.springframework.context.ApplicationContext;
    8.  
    9. @SpringBootApplication
    10. public class DemoApplication {
    11.  
    12.     public static void main(String[] args) {
    13.         //Spring 上下文
    14.         ApplicationContext context = SpringApplication.run(DemoApplication.class, args);
    15.         //返回的就是 Spring 的运行环境
    16.  
    17.         UserController bean = context.getBean(UserController.class);
    18.         bean.doController();
    19.  
    20.         UserService userService = context.getBean(UserService.class);
    21.         userService.doService();
    22.  
    23.         //根据名称来获取bean
    24.         UserService userService1 = (UserService) context.getBean("userService");
    25.         userService1.doService();
    26.  
    27.         //根据名称和类型来获取 bean
    28.         UserService userService2 = context.getBean("userService",UserService.class);
    29.         userService2.doService();
    30.     }

    ③  @Repository

    1. package com.example.ioc.repo;
    2.  
    3. import org.springframework.stereotype.Repository;
    4.  
    5. @Repository
    6. public class UserRepository {
    7.     public void doRepository(){
    8.         System.out.println("do repo...");
    9.     }
    10. }
    1. package com.example.ioc;
    2.  
    3. import com.example.ioc.controller.UserController;
    4. import com.example.ioc.repo.UserRepository;
    5. import com.example.ioc.service.UserService;
    6. import org.springframework.boot.SpringApplication;
    7. import org.springframework.boot.autoconfigure.SpringBootApplication;
    8. import org.springframework.context.ApplicationContext;
    9.  
    10. @SpringBootApplication
    11. public class DemoApplication {
    12.  
    13.     public static void main(String[] args) {
    14.         //Spring 上下文
    15.         ApplicationContext context = SpringApplication.run(DemoApplication.class, args);
    16.         //返回的就是 Spring 的运行环境
    17.  
    18.         UserController bean = context.getBean(UserController.class);
    19.         bean.doController();
    20.  
    21.         UserService userService = context.getBean(UserService.class);
    22.         userService.doService();
    23.  
    24.         //根据名称来获取bean
    25.         UserService userService1 = (UserService) context.getBean("userService");
    26.         userService1.doService();
    27.  
    28.         //根据名称和类型来获取 bean
    29.         UserService userService2 = context.getBean("userService",UserService.class);
    30.         userService2.doService();
    31.  
    32.         UserRepository userRepository = context.getBean(UserRepository.class);
    33.         userRepository.doRepository();
    34.     }

    ④  @Component

    1. package com.example.ioc.component;
    2.  
    3. import org.springframework.stereotype.Component;
    4.  
    5. @Component
    6. public class UserComponent {
    7.     public void doComponent(){
    8.         System.out.println("do component");
    9.     }
    10. }
    1. package com.example.ioc;
    2.  
    3. import com.example.ioc.component.UserComponent;
    4. import com.example.ioc.controller.UserController;
    5. import com.example.ioc.repo.UserRepository;
    6. import com.example.ioc.service.UserService;
    7. import org.springframework.boot.SpringApplication;
    8. import org.springframework.boot.autoconfigure.SpringBootApplication;
    9. import org.springframework.context.ApplicationContext;
    10.  
    11. @SpringBootApplication
    12. public class DemoApplication {
    13.  
    14.     public static void main(String[] args) {
    15.         //Spring 上下文
    16.         ApplicationContext context = SpringApplication.run(DemoApplication.class, args);
    17.         //返回的就是 Spring 的运行环境
    18.  
    19.         UserController bean = context.getBean(UserController.class);
    20.         bean.doController();
    21.  
    22.         UserService userService = context.getBean(UserService.class);
    23.         userService.doService();
    24.  
    25.         //根据名称来获取bean
    26.         UserService userService1 = (UserService) context.getBean("userService");
    27.         userService1.doService();
    28.  
    29.         //根据名称和类型来获取 bean
    30.         UserService userService2 = context.getBean("userService",UserService.class);
    31.         userService2.doService();
    32.  
    33.         UserRepository userRepository = context.getBean(UserRepository.class);
    34.         userRepository.doRepository();
    35.  
    36.         UserComponent userComponent = context.getBean(UserComponent.class);
    37.         userComponent.doComponent();
    38.     }
    39.  
    40. }

    ⑤  @Configuration

    1. package com.example.ioc.config;
    2.  
    3. import org.springframework.context.annotation.Configuration;
    4.  
    5. @Configuration
    6. public class UserConfig {
    7.     public void doConfig(){
    8.         System.out.println("do configurarion...");
    9.     }
    10. }
    1. package com.example.ioc;
    2.  
    3. import com.example.ioc.component.UserComponent;
    4. import com.example.ioc.config.UserConfig;
    5. import com.example.ioc.controller.UserController;
    6. import com.example.ioc.repo.UserRepository;
    7. import com.example.ioc.service.UserService;
    8. import org.springframework.boot.SpringApplication;
    9. import org.springframework.boot.autoconfigure.SpringBootApplication;
    10. import org.springframework.context.ApplicationContext;
    11.  
    12. @SpringBootApplication
    13. public class DemoApplication {
    14.  
    15.     public static void main(String[] args) {
    16.         //Spring 上下文
    17.         ApplicationContext context = SpringApplication.run(DemoApplication.class, args);
    18.         //返回的就是 Spring 的运行环境
    19.  
    20.         UserController bean = context.getBean(UserController.class);
    21.         bean.doController();
    22.  
    23.         UserService userService = context.getBean(UserService.class);
    24.         userService.doService();
    25.  
    26.         //根据名称来获取bean
    27.         UserService userService1 = (UserService) context.getBean("userService");
    28.         userService1.doService();
    29.  
    30.         //根据名称和类型来获取 bean
    31.         UserService userService2 = context.getBean("userService",UserService.class);
    32.         userService2.doService();
    33.  
    34.         UserRepository userRepository = context.getBean(UserRepository.class);
    35.         userRepository.doRepository();
    36.  
    37.         UserComponent userComponent = context.getBean(UserComponent.class);
    38.         userComponent.doComponent();
    39.  
    40.         UserConfig userConfig = context.getBean(UserConfig.class);
    41.         userConfig.doConfig();
    42.     }
    43.  
    44. }

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  • 原文地址：https://blog.csdn.net/qq_40841463/article/details/134441566