一 : 引言

经过前面的学习，我们已经可以实现基本的 Spring 读取和存储对象的操作了，但在操作的过程中我们发现读取和存储对象并没有想象中的那么“简单”，所以接下来我们要学习更加简单的操作 Bean 对象的方法 .

二 : 存储Bean对象

2.1 使用类注解

示例代码 :

运行结果 :

接下来我们对类注解进行一一验证 :

import com.component.UserComponent;
import com.configuration.UserConfiguration;
import com.controller.UserController;
import com.respository.UserRepository;
import com.service.UserService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.stereotype.Controller;
//启动类
public class Test {public static void main(String[] args) {//1.得到Spring上下文对象ApplicationContext context =new ClassPathXmlApplicationContext("spring-config.xml");//2.从Spring获取bean对象[使用注解,默认命名规则:类名首字母小写]UserService userService = (UserService) context.getBean("userService");//3.使用beanuserService.doService();UserRepository userRepository = (UserRepository) context.getBean("userRepository");userRepository.doRepository();UserComponent userComponent = (UserComponent) context.getBean("userComponent");userComponent.doComponent();UserConfiguration userConfiguration = (UserConfiguration) context.getBean("userConfiguration");userConfiguration.doConfiguration();UserController userController = (UserController) context.getBean("userController");userController.doUserController();}
}

代码结构基本一致 :

运行结果 :

Q1 : 5大类注解的关系 ?

@Controller、@Service、@Repository、@Configuration 都是基于@Component，它们的作用都是将Bean存储到Spring 中 .

Q2 : Bean的命名规则 ?

查看Bean命名的源码 :

2.2 使用方法注解

2.2.1 演示

方法注解Bean命名规则 :

2.2.2注意事项

2.2.3 @Bean重命名

方法一:@Bean(name="xxxxx")

package com.bean;import com.model.User;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Controller;@Controller
public class UserBean {@Bean(name = "computerUser")public User user1() {User user = new User();user.setAge(18);user.setName("百乔");return user;}
}

import com.model.User;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class Test2 {public static void main(String[] args) {//1.得到Spring上下文对象ApplicationContext context =new ClassPathXmlApplicationContext("spring-config.xml");//2.从Spring获取bean对象[使用注解,默认命名规则:类名首字母小写]User user = (User) context.getBean("computerUser");//3.使用beanSystem.out.println(user);}
}

方法二:@Bean("xxxxx")

package com.bean;import com.model.User;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Controller;@Controller
public class UserBean {@Bean("computerUser")public User user1() {User user = new User();user.setAge(18);user.setName("百乔");return user;}
}

import com.model.User;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class Test2 {public static void main(String[] args) {//1.得到Spring上下文对象ApplicationContext context =new ClassPathXmlApplicationContext("spring-config.xml");//2.从Spring获取bean对象[使用注解,默认命名规则:类名首字母小写]User user = (User) context.getBean("computerUser");//3.使用beanSystem.out.println(user);}
}

方法三 : @Bean("xxxx","xxxxxx")

package com.bean;import com.model.User;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Controller;@Controller
public class UserBean {@Bean(name = {"computerUser","blackboardUser"})public User user1() {User user = new User();user.setAge(18);user.setName("百乔");return user;}
}

import com.model.User;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class Test2 {public static void main(String[] args) {//1.得到Spring上下文对象ApplicationContext context =new ClassPathXmlApplicationContext("spring-config.xml");//2.从Spring获取bean对象[使用注解,默认命名规则:类名首字母小写]User user = (User) context.getBean("blackboardUser");//3.使用beanSystem.out.println(user);}
}

三 : 获取Bean对象(依赖注入/对象装配)

在 Spring 中实现依赖注入的常见方式有以下 3 种：

• 属性注入（Field Injection）；
• Setter 注入（Setter Injection）；
• 构造方法注入（Constructor Injection）.

3.1 属性注入

属性注入是我们最熟悉，也是日常开发中使用最多的一种注入方式.

package com.controller;import com.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;@Controller
public class UserController {//1.属性注入@Autowired // 自动装配private UserService userService;public void doUserController() {System.out.println("Do UserController!");userService.doService();}
}

import com.controller.UserController;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class Test3 {public static void main(String[] args) {ApplicationContext context =new ClassPathXmlApplicationContext("spring-config.xml");UserController userController = (UserController) context.getBean("userController");userController.doUserController();}
}

3.2 Setter注入

package com.controller;import com.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;@Controller
public class UserController {//2.Setter注入private UserService userService;@Autowiredpublic void setUserService(UserService userService) {this.userService = userService;}public void doUserController() {System.out.println("Do UserController!");userService.doService();}
}

import com.controller.UserController;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class Test3 {public static void main(String[] args) {ApplicationContext context =new ClassPathXmlApplicationContext("spring-config.xml");UserController userController = (UserController) context.getBean("userController");userController.doUserController();}
}

3.3 构造方法注入

package com.controller;import com.model.User;
import com.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;@Controller
public class UserController {//3.构造方法注入private  UserService userService;@Autowiredpublic UserController(UserService userService) {this.userService = userService;}public void doUserController() {System.out.println("Do UserController!");userService.doService();}
}

import com.controller.UserController;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class Test3 {public static void main(String[] args) {ApplicationContext context =new ClassPathXmlApplicationContext("spring-config.xml");UserController userController = (UserController) context.getBean("userController");userController.doUserController();}
}

以下是关于构造方法注入的一些注意事项 :

1.当当前类只有一个构造方法时,@Autowired可以省略;当存在多个构造方法时,@Autowired注解不能省略.

2.可以在一个构造方法里注入多个Autowired对象,且当仅有1个构造方法时,@Autowired可以省略.

package com.controller;import com.configuration.UserConfiguration;
import com.model.User;
import com.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;@Controller
public class UserController {//3.构造方法注入private UserService userService;private UserConfiguration userConfiguration;@Autowiredpublic UserController(UserService userService,UserConfiguration userConfiguration) {this.userService = userService;this.userConfiguration = userConfiguration;}public void doUserController() {System.out.println("Do UserController!");userService.doService();userConfiguration.doConfiguration();}
}

import com.controller.UserController;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class Test3 {public static void main(String[] args) {ApplicationContext context =new ClassPathXmlApplicationContext("spring-config.xml");UserController userController = (UserController) context.getBean("userController");userController.doUserController();}
}

3.答:当有多个构造方法的时候，加了@Autowired 的构造方法才会执行，并且构造方法中的参数(对象）必须要存在于Spring容器中，否则就会报错.

典型错误 :

构造方法注入的优点 :

Spring4.2之前推荐使用Setter注入方式 , 原因是其符合单一性原则 ; Spring4.2之后则推荐使用构造方法注入 . 有意思的是Spring官方在源代码中更多使用的 , 却是属性注入的方式 , 因为这种方法确实非常简单 .

3.2 @Resource

在进行类注入时，除了可以使用 @Autowired 关键字之外，我们还可以使用 @Resource 进行注入 , 示例如下 :

@Resource注解不能使用在构造方法实现上 .

@Resource和@Autowired的区别

先看@Resource :

package com.controller;
import com.model.User;
import org.springframework.stereotype.Controller;import javax.annotation.Resource;@Controller
public class SheepController {@Resource(name = "user1")private User user;public void doSheepController() {System.out.println("别看我只是一只羊");System.out.println(user);}
}

import com.controller.SheepController;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class Test3 {public static void main(String[] args) {ApplicationContext context =new ClassPathXmlApplicationContext("spring-config.xml");SheepController sheepController =(SheepController) context.getBean("sheepController");sheepController.doSheepController();}
}

解释 :

如果使用@Autowired , 需要配合另一个Spring的注解@qualifier .

还可以配合@Primary注解 :

以下是一道综合练习题 , 大家可以到我的码云(SpringBoot_Demo3)查看答案 :

本节内容结束 !