spring —— IoC容器（二）

二、基于注解管理 bean

（一）Autowired 主动装配

（1）属性上主动装配

1. package com.fourth.anno;
3. import org.springframework.stereotype.Component;
5. @Component
6. public class Dao {
7.     public void runDao(){
8.         System.out.println("hello world");
9.     }
10. }

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1. package com.fourth.anno;
3. import org.springframework.beans.factory.annotation.Autowired;
4. import org.springframework.stereotype.Component;
6. @Component
7. public class Service {
8.     @Autowired
9.     private Dao dao;
10.     public void runService(){
11.         dao.runDao();
12.     }
13. }

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1. package com.fourth.anno;
3. import org.springframework.context.ApplicationContext;
4. import org.springframework.context.support.ClassPathXmlApplicationContext;
6. public class Test {
7.     public static void main(String[] args) {
8.         ApplicationContext context = new ClassPathXmlApplicationContext("bean-anno.xml");
9.         Service service = context.getBean(Service.class);
10.         service.runService();
11.     }
12. }

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1. <?xml version="1.0" encoding="UTF-8"?>
2. <beans xmlns="http://www.springframework.org/schema/beans"
3.        xmlns:context="http://www.springframework.org/schema/context"
4.        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
5.        xsi:schemaLocation="
6.        http://www.springframework.org/schema/context
7.        http://www.springframework.org/schema/context/spring-context.xsd
8.        http://www.springframework.org/schema/beans
9.        http://www.springframework.org/schema/beans/spring-beans.xsd">
11.     <context:component-scan base-package="com.fourth.anno"></context:component-scan>
12. </beans>

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（2）set 方法上主动装配 

1. package com.fourth.anno;
3. import org.springframework.beans.factory.annotation.Autowired;
4. import org.springframework.stereotype.Component;
6. @Component
7. public class Service {   
8.     private Dao dao;
10.     @Autowired
11.     public void setDao(Dao dao){
12.         this.dao=dao;
13.     }
15.     public void runService(){
16.         dao.runDao();
17.     }
18. }

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（3）构造方法上主动装配 

1. package com.fourth.anno;
3. import org.springframework.beans.factory.annotation.Autowired;
4. import org.springframework.stereotype.Component;
6. @Component
7. public class Service {
9.     private Dao dao;
10.     @Autowired
11.     public Service(Dao dao) {
12.         this.dao = dao;
13.     }
15.     public void runService(){
16.         dao.runDao();
17.     }
18. }

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（4）构造方法的形参上主动装配 

1. package com.fourth.anno;
3. import org.springframework.beans.factory.annotation.Autowired;
4. import org.springframework.stereotype.Component;
6. @Component
7. public class Service {
9.     private Dao dao;
11.     public Service(@Autowired Dao dao) {
12.         this.dao = dao;
13.     }
15.     public void runService(){
16.         dao.runDao();
17.     }
18. }

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 （二）Resource 主动装配

（1）属性上主动装配

1. package com.fourth.anno;
3. import jakarta.annotation.Resource;
4. import org.springframework.stereotype.Component;
6. @Component
7. public class Service {
8.     @Resource
9.     private Dao dao;
11.     public void runService(){
12.         dao.runDao();
13.     }
14. }

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（2）set 方法上主动装配 

1. package com.fourth.anno;
3. import jakarta.annotation.Resource;
4. import org.springframework.stereotype.Component;
6. @Component
7. public class Service {
9.     private Dao dao;
10.     @Resource
11.     public void setDao(Dao dao) {
12.         this.dao = dao;
13.     }
15.     public void runService(){
16.         dao.runDao();
17.     }
18. }

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 Autowired 与 Resource 比较：

Autowired 可以应用在属性、set 方法、构造方法、构造方法的形参上；其默认通过范例进行装配。
Resource 可以应用在属性、set 方法上；其默认通过名称进行装配。
 Autowired 基于 spring 框架；Resource 基于 java 扩展包，假如 JDK 版本高于11或低于8，应引入以下依赖：

1. <strong><dependency>
2.     <groupId>jakarta.annotation</groupId>
3.     <artifactId>jakarta.annotation-api</artifactId>
4.     <version>2.1.1</version>
5. </dependency></strong>

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（三）全注解开发

全注解开发，纵然用配置类代替 xml 配置文件：

1. package com.fourth.anno;
3. import org.springframework.stereotype.Component;
5. @Component
6. public class Dao {
7.     public void runDao(){
8.         System.out.println("hello world");
9.     }
10. }

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1. package com.fourth.anno;
3. import jakarta.annotation.Resource;
4. import org.springframework.stereotype.Component;
6. @Component
7. public class Service {
9.     private Dao dao;
10.     @Resource
11.     public void setDao(Dao dao) {
12.         this.dao = dao;
13.     }
15.     public void runService(){
16.         dao.runDao();
17.     }
18. }

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1. package com.fourth.anno;
3. import org.springframework.context.annotation.ComponentScan;
4. import org.springframework.context.annotation.Configuration;
6. @Configuration
7. @ComponentScan(value = "com.fourth.anno")
8. public class SpringConfig {
9. }

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1. package com.fourth.anno;
3. import org.springframework.context.ApplicationContext;
4. import org.springframework.context.annotation.AnnotationConfigApplicationContext;
6. public class Test {
7.     public static void main(String[] args) {
8.         ApplicationContext context = new AnnotationConfigApplicationContext(SpringConfig.class);
9.         Service service = context.getBean(Service.class);
10.         service.runService();
11.     }
12. }

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