@Resource注解源码分析
xuchengsheng
parent
41a77cae00
commit
3afe054788
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@ -23,6 +23,7 @@
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<module>spring-annotation-conditional</module>
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<module>spring-annotation-value</module>
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<module>spring-annotation-autowired</module>
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<module>spring-annotation-profile</module>
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</modules>
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</project>
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@ -0,0 +1 @@
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## TODO
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@ -0,0 +1,19 @@
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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<parent>
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<artifactId>spring-annotation</artifactId>
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<groupId>com.xcs.spring</groupId>
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<version>0.0.1-SNAPSHOT</version>
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</parent>
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<modelVersion>4.0.0</modelVersion>
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<artifactId>spring-annotation-profile</artifactId>
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<properties>
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<maven.compiler.source>11</maven.compiler.source>
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<maven.compiler.target>11</maven.compiler.target>
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</properties>
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</project>
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@ -30,6 +30,11 @@
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<artifactId>javax.inject</artifactId>
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<version>1</version>
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</dependency>
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<dependency>
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<groupId>jakarta.annotation</groupId>
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<artifactId>jakarta.annotation-api</artifactId>
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<version>1.3.5</version>
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</dependency>
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</dependencies>
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</project>
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@ -1 +1,198 @@
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## TODO
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## @Resource
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### 一、基本信息
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✒️ **作者** - Lex 📝 **博客** - [我的CSDN](https://blog.csdn.net/duzhuang2399/article/details/133887864) 📚 **文章目录** - [所有文章](https://github.com/xuchengsheng/spring-reading) 🔗 **源码地址** - [@Resource源码](https://github.com/xuchengsheng/spring-reading/blob/master/spring-jsr/spring-jsr250-resource)
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### 二、接口描述
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`@Resource` 注解是由 JSR-250: Common Annotations for the Java Platform 规范定义的。这个规范定义了一组跨多个 Java 技术（如 Java EE 和 Java SE）的公共注解。
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### 三、接口源码
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`@Resource` 注解的目的是为了声明和注入应用程序所需的外部资源，从而允许容器在运行时为应用程序组件提供这些资源。
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```java
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/**
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* 标注需要注入的资源的注解。
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* 这个注解可以用于类、字段和方法上，指示容器为其注入资源。
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*/
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@Target({ElementType.TYPE, ElementType.FIELD, ElementType.METHOD})
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@Retention(RetentionPolicy.RUNTIME)
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@Repeatable(Resources.class)
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public @interface Resource {
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/**
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* 资源的 JNDI 名称。
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*
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* @return 资源名称。
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*/
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String name() default "";
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/**
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* JNDI 查询名称，用于运行时查找资源。
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*
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* @return JNDI 查询名称。
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*/
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String lookup() default "";
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/**
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* 资源的期望类型。默认为 Object，意味着类型不特定。
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*
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* @return 资源类型。
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*/
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Class<?> type() default Object.class;
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/**
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* 资源的身份验证类型。
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*
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* @return 身份验证类型。
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*/
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Resource.AuthenticationType authenticationType() default Resource.AuthenticationType.CONTAINER;
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/**
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* 标示资源是否可以被多个客户端共享。
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*
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* @return 如果资源可以被共享则返回 true，否则返回 false。
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*/
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boolean shareable() default true;
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/**
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* 与资源环境引用关联的产品特定的名称。
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*
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* @return 映射名称。
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*/
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String mappedName() default "";
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/**
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* 对资源的简要描述。
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*
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* @return 资源描述。
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*/
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String description() default "";
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/**
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* 身份验证类型的枚举。
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* CONTAINER: 容器管理身份验证。
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* APPLICATION: 应用程序管理身份验证。
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*/
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public static enum AuthenticationType {
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CONTAINER,
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APPLICATION;
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}
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}
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```
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### 四、主要功能
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1. **资源定位**
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+ 通过 `name` 和 `lookup` 属性，`@Resource` 可以定位到特定的资源，如 JNDI 中的一个数据库连接。
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2. **类型指定**
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+ 通过 `type` 属性，它允许指定所需资源的具体Java类型，确保注入的资源与预期类型匹配，从而提供类型安全。
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3. **身份验证策略**
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+ `authenticationType` 属性允许开发者选择资源的身份验证方式，决定是由容器还是应用程序来进行身份验证。
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4. **共享策略**
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+ 通过 `shareable` 属性，它指定资源是否可以在多个客户端或组件之间共享。
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5. **供应商特定名称**
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+ `mappedName` 属性可以提供与资源关联的供应商或平台特定的名称，增加部署的灵活性。
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6. **描述信息**
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+ 通过 `description` 属性，为资源提供了简要描述，有助于开发者和系统管理员理解其用途。
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### 五、最佳实践
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首先来看看启动类入口，上下文环境使用`AnnotationConfigApplicationContext`（此类是使用Java注解来配置Spring容器的方式），构造参数我们给定了一个`MyConfiguration`组件类。然后从Spring上下文中获取一个`MyController`类型的bean并调用了`showService`方法，
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```java
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public class ResourceApplication {
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public static void main(String[] args) {
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AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(MyConfiguration.class);
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MyController controller = context.getBean(MyController.class);
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controller.showService();
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}
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}
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```
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在`MyConfiguration`类中，使用了`@ComponentScan("com.xcs.spring")`注解告诉 Spring 在指定的包（在这里是 "`com.xcs.spring`"）及其子包中搜索带有 `@Component`、`@Service`、`@Repository` 和 `@Controller` 等注解的类，并将它们自动注册为 beans。这样，spring就不必为每个组件明确写一个 bean 定义。Spring 会自动识别并注册它们。
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```java
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@Configuration
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@ComponentScan("com.xcs.spring")
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public class MyConfiguration {
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}
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```
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Spring 容器在初始化 `MyController` 时，我们使用了`@Resource`注解，会自动注入一个 `MyService` 类型的 bean 到 `myService` 字段。
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```java
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@Controller
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public class MyController {
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@Resource(name="myService")
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private MyService myService;
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public void showService(){
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System.out.println("myService = " + myService);
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}
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}
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```
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`MyService` 是一个简单的服务类，但我们没有定义任何方法或功能。
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```java
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@Service
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public class MyService {
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}
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```
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运行结果发现，我们使用 `@Resource` 注解的功能，在我们的 Spring 上下文中工作正常，并且它成功地自动注入了所需的依赖关系。
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```java
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myService = com.xcs.spring.service.MyService@f0c8a99
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```
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### 六、时序图
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~~~mermaid
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sequenceDiagram
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Title: @Resource注解时序图
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AbstractAutowireCapableBeanFactory->>AbstractAutowireCapableBeanFactory:applyMergedBeanDefinitionPostProcessors(mbd,beanType,beanName)<br>应用Bean定义的后置处理器
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AbstractAutowireCapableBeanFactory->>CommonAnnotationBeanPostProcessor:postProcessMergedBeanDefinition(beanDefinition,beanType,beanName)<br>处理已合并的Bean定义
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CommonAnnotationBeanPostProcessor->>CommonAnnotationBeanPostProcessor:findResourceMetadata(beanName,clazz,pvs)
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CommonAnnotationBeanPostProcessor->>CommonAnnotationBeanPostProcessor:buildResourceMetadata(clazz)
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CommonAnnotationBeanPostProcessor->>ReflectionUtils:doWithLocalFields(clazz,fc)<br>处理类的本地字段
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ReflectionUtils->>CommonAnnotationBeanPostProcessor:解析有@Resource注解的字段
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CommonAnnotationBeanPostProcessor->>ResourceElement:ResourceElement(member,ae,pd)
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CommonAnnotationBeanPostProcessor->>ReflectionUtils:doWithLocalMethods(clazz,fc)<br>处理类的本地方法
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ReflectionUtils->>CommonAnnotationBeanPostProcessor:解析有@Resource注解的方法
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CommonAnnotationBeanPostProcessor->>ResourceElement:ResourceElement(member,ae,pd)
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CommonAnnotationBeanPostProcessor->>CommonAnnotationBeanPostProcessor:injectionMetadataCache.put(cacheKey, metadata)<br>将元数据存入缓存
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AbstractAutowireCapableBeanFactory->>AbstractAutowireCapableBeanFactory:populateBean(beanName,mbd,bw)<br>填充Bean的属性值
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AbstractAutowireCapableBeanFactory->>CommonAnnotationBeanPostProcessor:postProcessProperties(pvs,bean,beanName)<br>后处理Bean的属性
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CommonAnnotationBeanPostProcessor->>CommonAnnotationBeanPostProcessor:findResourceMetadata(beanName,clazz,pvs)
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Note right of CommonAnnotationBeanPostProcessor:<br>从缓存中获取注入的元数据
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CommonAnnotationBeanPostProcessor->>InjectionMetadata:inject(target,beanName,pvs)
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InjectionMetadata->>InjectedElement:inject(target,requestingBeanName,pvs)
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InjectedElement->>ResourceElement:getResourceToInject(target,requestingBeanName)
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ResourceElement->>CommonAnnotationBeanPostProcessor:getResource(element,requestingBeanName)
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CommonAnnotationBeanPostProcessor->>CommonAnnotationBeanPostProcessor:autowireResource(factory,element,requestingBeanName)
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CommonAnnotationBeanPostProcessor->>AbstractAutowireCapableBeanFactory:resolveBeanByName(name,descriptor)
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AbstractAutowireCapableBeanFactory->>CommonAnnotationBeanPostProcessor:返回被依赖的Bean
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CommonAnnotationBeanPostProcessor->>ResourceElement:返回被依赖的Bean
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ResourceElement->>InjectedElement:返回被依赖的Bean
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InjectedElement->>Field:field.set(target, 返回被依赖的Bean)
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~~~
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### 七、源码分析
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### 八、注意事项
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### 九、总结
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#### 最佳实践总结
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#### 源码分析总结
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@ -7,13 +7,8 @@
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<groupId>com.xcs.spring</groupId>
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<version>0.0.1-SNAPSHOT</version>
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</parent>
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<modelVersion>4.0.0</modelVersion>
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<modelVersion>4.0.0</modelVersion>
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<artifactId>spring-jsr250-resource</artifactId>
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<properties>
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<maven.compiler.source>11</maven.compiler.source>
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<maven.compiler.target>11</maven.compiler.target>
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</properties>
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</project>
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@ -0,0 +1,18 @@
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package com.xcs.spring;
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import com.xcs.spring.config.MyConfiguration;
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import com.xcs.spring.controller.MyController;
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import org.springframework.context.annotation.AnnotationConfigApplicationContext;
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/**
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* @author xcs
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* @date 2023年08月07日 16时21分
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**/
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public class ResourceApplication {
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public static void main(String[] args) {
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AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(MyConfiguration.class);
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MyController controller = context.getBean(MyController.class);
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controller.showService();
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}
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}
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@ -0,0 +1,10 @@
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package com.xcs.spring.config;
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import org.springframework.context.annotation.ComponentScan;
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import org.springframework.context.annotation.Configuration;
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@Configuration
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@ComponentScan("com.xcs.spring")
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public class MyConfiguration {
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}
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@ -0,0 +1,18 @@
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package com.xcs.spring.controller;
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import com.xcs.spring.service.MyService;
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import org.springframework.stereotype.Controller;
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import javax.annotation.Resource;
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import javax.inject.Inject;
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@Controller
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public class MyController {
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@Resource(name="myService")
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private MyService myService;
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public void showService(){
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System.out.println("myService = " + myService);
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}
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}
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@ -0,0 +1,7 @@
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package com.xcs.spring.service;
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import org.springframework.stereotype.Service;
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@Service
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public class MyService {
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}
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