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标题: 8、Spring之基于注解的自动装配 [打印本页]
作者: 络腮胡菲菲    时间: 2023-8-7 23:40
标题: 8、Spring之基于注解的自动装配
8.1、场景模拟

8.1.1、UserDao接口及实现类

  1. package org.rain.spring.dao;
  3. /**
  4. * @author liaojy
  5. * @date 2023/8/5 - 18:32
  6. */
  7. public interface UserDao {
  9.     void saveUser();
  11. }
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  1. package org.rain.spring.dao.impl;
  3. import org.rain.spring.dao.UserDao;
  4. import org.springframework.stereotype.Repository;
  6. /**
  7. * @author liaojy
  8. * @date 2023/8/5 - 18:33
  9. */
  10. @Repository
  11. public class UserDaoImpl implements UserDao {
  12.     public void saveUser() {
  13. <?xml version="1.0" encoding="UTF-8"?>
  14. <beans xmlns="http://www.springframework.org/schema/beans"
  15.        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  16.        xmlns:context="http://www.springframework.org/schema/context"
  17.        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
  19.    
  20.     <context:component-scan base-package="org.rain.spring"></context:component-scan>
  22. </beans>System.out.println("保存成功");
  23.     }
  24. }
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8.1.2、UserService接口及实现类

  1. package org.rain.spring.service;
  3. /**
  4. * @author liaojy
  5. * @date 2023/8/5 - 18:35
  6. */
  7. public interface UserService {
  9.     void saveUser();
  11. }
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  1. package org.rain.spring.service.impl;
  3. import org.rain.spring.dao.UserDao;
  4. import org.rain.spring.service.UserService;
  5. import org.springframework.stereotype.Service;
  7. /**
  8. * @author liaojy
  9. * @date 2023/8/5 - 18:36
  10. */
  11. @Service
  12. public class UserServiceImpl implements UserService {
  14.     private UserDao userDao;
  16.     public void saveUser() {
  17. <?xml version="1.0" encoding="UTF-8"?>
  18. <beans xmlns="http://www.springframework.org/schema/beans"
  19.        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  20.        xmlns:context="http://www.springframework.org/schema/context"
  21.        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
  23.    
  24.     <context:component-scan base-package="org.rain.spring"></context:component-scan>
  26. </beans>userDao.saveUser();
  27.     }
  29. }
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8.1.3、UserController

  1. package org.rain.spring.controller;
  3. import org.rain.spring.service.UserService;
  4. import org.springframework.stereotype.Controller;
  6. /**
  7. * @author liaojy
  8. * @date 2023/8/5 - 18:38
  9. */
  10. @Controller("myUserController")
  11. public class UserController {
  13.     private UserService userService;
  15.     public void saveUser(){
  16. <?xml version="1.0" encoding="UTF-8"?>
  17. <beans xmlns="http://www.springframework.org/schema/beans"
  18.        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  19.        xmlns:context="http://www.springframework.org/schema/context"
  20.        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
  22.    
  23.     <context:component-scan base-package="org.rain.spring"></context:component-scan>
  25. </beans>userService.saveUser();
  26.     }
  28. }
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8.1.4、bean配置

  1. <?xml version="1.0" encoding="UTF-8"?>
  2. <beans xmlns="http://www.springframework.org/schema/beans"
  3.        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  4.        xmlns:context="http://www.springframework.org/schema/context"
  5.        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
  7.    
  8.     <context:component-scan base-package="org.rain.spring"></context:component-scan>
  10. </beans>
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8.1.5、测试


由控制台日志可知，组件注解+组件扫描，存在尚未实现依赖注入的问题
  1.     @Test    public void testAutowireByAnnotation(){<?xml version="1.0" encoding="UTF-8"?>
  2. <beans xmlns="http://www.springframework.org/schema/beans"
  3.        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  4.        xmlns:context="http://www.springframework.org/schema/context"
  5.        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
  7.    
  8.     <context:component-scan base-package="org.rain.spring"></context:component-scan>
  10. </beans>ApplicationContext ioc = new ClassPathXmlApplicationContext("spring-ioc-annotation.xml");<?xml version="1.0" encoding="UTF-8"?>
  11. <beans xmlns="http://www.springframework.org/schema/beans"
  12.        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  13.        xmlns:context="http://www.springframework.org/schema/context"
  14.        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
  16.    
  17.     <context:component-scan base-package="org.rain.spring"></context:component-scan>
  19. </beans>UserController userController = ioc.getBean(UserController.class);<?xml version="1.0" encoding="UTF-8"?>
  20. <beans xmlns="http://www.springframework.org/schema/beans"
  21.        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  22.        xmlns:context="http://www.springframework.org/schema/context"
  23.        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
  25.    
  26.     <context:component-scan base-package="org.rain.spring"></context:component-scan>
  28. </beans>userController.saveUser();    }
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8.2、@Autowired注解

@Autowired：实现自动装配功能的注解，其能够标识的位置有三处
8.2.1、方式一：标识在成员变量上(常用)

  1.     @Autowired
  2.     private UserDao userDao;
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  1.     @Autowired
  2.     private UserService userService;
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8.2.2、方式二：标识在setter方法上

  1.     private UserDao userDao;    @Autowired    public void setUserDao(UserDao userDao) {<?xml version="1.0" encoding="UTF-8"?>
  2. <beans xmlns="http://www.springframework.org/schema/beans"
  3.        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  4.        xmlns:context="http://www.springframework.org/schema/context"
  5.        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
  7.    
  8.     <context:component-scan base-package="org.rain.spring"></context:component-scan>
  10. </beans>this.userDao = userDao;    }
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  1.     private UserService userService;    @Autowired    public void setUserService(UserService userService) {<?xml version="1.0" encoding="UTF-8"?>
  2. <beans xmlns="http://www.springframework.org/schema/beans"
  3.        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  4.        xmlns:context="http://www.springframework.org/schema/context"
  5.        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
  7.    
  8.     <context:component-scan base-package="org.rain.spring"></context:component-scan>
  10. </beans>this.userService = userService;    }
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8.2.3、方式三：标识在有参构造方法上

  1.     private UserDao userDao;    @Autowired    public UserServiceImpl(UserDao userDao) {<?xml version="1.0" encoding="UTF-8"?>
  2. <beans xmlns="http://www.springframework.org/schema/beans"
  3.        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  4.        xmlns:context="http://www.springframework.org/schema/context"
  5.        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
  7.    
  8.     <context:component-scan base-package="org.rain.spring"></context:component-scan>
  10. </beans>this.userDao = userDao;    }
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  1.     private UserService userService;    @Autowired    public UserController(UserService userService) {<?xml version="1.0" encoding="UTF-8"?>
  2. <beans xmlns="http://www.springframework.org/schema/beans"
  3.        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  4.        xmlns:context="http://www.springframework.org/schema/context"
  5.        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
  7.    
  8.     <context:component-scan base-package="org.rain.spring"></context:component-scan>
  10. </beans>this.userService = userService;    }
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8.3、@Autowired的工作流程


如果有多个类型匹配的bean，且在IOC容器中没有找到id和属性名相同的bean，也没有使用@Qualifier注解指定将某个bean赋值给属性；则会抛出异常NoUniqueBeanDefinitionException
  1.     @Autowired
  2.     @Qualifier("myUserService")
  3.     private UserService userService;
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8.4、@Autowired的注意事项

在@Autowired注解中有一个属性required，默认值为true，意思是必要完成自动装配
如果在IOC容器中没有匹配的bean，就会抛出异常NoSuchBeanDefinitionException
为此可以将required属性的值设置为false，这样能装配就装配，不能装配就使用默认值

一般可以通过排查组件注解、组件扫描和@Qualifier注解，定位出为什么在IOC容器中没有匹配的bean
  1.     @Autowired(required = false)
  2.     private UserService userService;
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