166 lines
8.5 KiB
Markdown
166 lines
8.5 KiB
Markdown
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## AnnotationConfigApplicationContext
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- [AnnotationConfigApplicationContext](#annotationconfigapplicationcontext)
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- [一、基本信息](#一基本信息)
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- [二、知识储备](#二知识储备)
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- [三、基本描述](#三基本描述)
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- [四、最佳实践](#四最佳实践)
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- [五、时序图](#五时序图)
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- [六、源码分析](#六源码分析)
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### 一、基本信息
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✒️ **作者** - Lex 📝 **博客** - [掘金](https://juejin.cn/user/4251135018533068/posts) 📚 **源码地址** - [github](https://github.com/xuchengsheng/spring-reading)
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### 二、知识储备
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+ **ClassPathBeanDefinitionScanner**
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+ [ClassPathBeanDefinitionScanner](https://github.com/xuchengsheng/spring-reading/blob/master/spring-beans/spring-bean-classPathBeanDefinitionScanner/README.md) 类，用于在类路径上扫描指定包及其子包中的类，识别符合条件的类，并将其注册为 Spring Bean 的定义，从而实现组件扫描和自动装配，使我们能够方便地管理和配置应用程序中的 Bean。它允许我们定义过滤条件，以确定哪些类应被注册为 Bean，以及配合自动装配实现依赖注入，提高了应用程序的可维护性和扩展性。
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+ **AnnotatedBeanDefinitionReader**
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+ [AnnotatedBeanDefinitionReader](https://github.com/xuchengsheng/spring-reading/blob/master/spring-beans/spring-bean-annotatedBeanDefinitionReader/README.md)是一个用于读取和解析带有注解的Bean定义的类，它主要用于基于注解的配置方式，允许开发者将Java类标记为Spring组件，从而让Spring容器自动扫描和注册这些组件，而不需要显式配置这些组件的Bean定义。
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### 三、基本描述
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`AnnotationConfigApplicationContext` 提供了一种基于 Java 注解的轻量级、类型安全的方式来配置和管理 Spring 容器中的 bean。这种方式相对于传统的 XML 配置方式更加灵活，并且有助于减少配置文件的数量和复杂性。
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### 四、最佳实践
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通过`AnnotationConfigApplicationContext`容器，以手动注册和包扫描两种方式注册Bean定义，其中手动注册了单个Bean（`MyBean`类），并通过包扫描注册了指定包路径下的所有标有`@Component`及其派生注解的类。最后，通过打印输出了所有已注册的Bean定义的名称。
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```java
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public class RegisterBeanDefinitionApplication {
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public static void main(String[] args) {
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AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
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// 注册Bean
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context.register(MyBean.class);
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// 扫描包
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context.scan("com.xcs.spring");
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// 打印Bean定义
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for (String beanDefinitionName : context.getBeanDefinitionNames()) {
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System.out.println("beanDefinitionName = " + beanDefinitionName);
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}
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}
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}
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```
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一个简单的Java类 `MyBean`，这个类没有任何注解或其他特殊标记。
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```java
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public class MyBean {
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}
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```
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分别使用`@Controller`、`@Service`和`@Repository`。这些注解是Spring框架中用于标识不同层次组件的特殊注解。
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```java
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@Controller
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public class MyController {
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}
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@Service
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public class MyService {
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}
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@Repository
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public class MyRepository {
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}
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```
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运行结果发现，Spring应用上下文中成功加载了配置，并注册了各种Bean定义，包括手动注册和通过注解自动注册的。
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PS：前面4个是Spring容器内部的注册的Bean定义。
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```java
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beanDefinitionName = org.springframework.context.annotation.internalConfigurationAnnotationProcessor
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beanDefinitionName = org.springframework.context.annotation.internalAutowiredAnnotationProcessor
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beanDefinitionName = org.springframework.context.event.internalEventListenerProcessor
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beanDefinitionName = org.springframework.context.event.internalEventListenerFactory
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beanDefinitionName = myBean
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beanDefinitionName = myController
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beanDefinitionName = myRepository
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beanDefinitionName = myService
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```
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### 五、时序图
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~~~mermaid
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sequenceDiagram
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Title: AnnotationConfigApplicationContext时序图
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AnnotationConfigApplicationContextDemo->>AnnotationConfigApplicationContext: AnnotationConfigApplicationContext()
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Note over AnnotationConfigApplicationContextDemo,AnnotationConfigApplicationContext: 创建 AnnotationConfigApplicationContext 实例
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AnnotationConfigApplicationContext->>AnnotatedBeanDefinitionReader: new AnnotatedBeanDefinitionReader(this)
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Note over AnnotationConfigApplicationContext,AnnotatedBeanDefinitionReader: 创建 AnnotatedBeanDefinitionReader 实例
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AnnotatedBeanDefinitionReader->>AnnotationConfigApplicationContext: 返回 AnnotatedBeanDefinitionReader
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Note over AnnotatedBeanDefinitionReader,AnnotationConfigApplicationContext: 获取 AnnotatedBeanDefinitionReader 实例
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AnnotationConfigApplicationContext->>ClassPathBeanDefinitionScanner: new ClassPathBeanDefinitionScanner(this)
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Note over AnnotationConfigApplicationContext,ClassPathBeanDefinitionScanner: 创建 ClassPathBeanDefinitionScanner 实例
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ClassPathBeanDefinitionScanner->>AnnotationConfigApplicationContext: 返回 ClassPathBeanDefinitionScanner
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Note over ClassPathBeanDefinitionScanner,AnnotationConfigApplicationContext: 获取 ClassPathBeanDefinitionScanner 实例
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AnnotationConfigApplicationContextDemo->>AnnotationConfigApplicationContext: register(componentClasses)
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Note over AnnotationConfigApplicationContextDemo,AnnotationConfigApplicationContext: 注册组件类
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AnnotationConfigApplicationContext->>AnnotatedBeanDefinitionReader: this.reader.register(componentClasses)
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Note over AnnotationConfigApplicationContext,AnnotatedBeanDefinitionReader: 使用 AnnotatedBeanDefinitionReader 注册组件类
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AnnotationConfigApplicationContextDemo->>AnnotationConfigApplicationContext: scan(basePackages)
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Note over AnnotationConfigApplicationContextDemo,AnnotationConfigApplicationContext: 扫描指定包
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AnnotationConfigApplicationContext->>ClassPathBeanDefinitionScanner: this.scanner.scan(basePackages)
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Note over AnnotationConfigApplicationContext,ClassPathBeanDefinitionScanner: 使用 ClassPathBeanDefinitionScanner 扫描包
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~~~
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### 六、源码分析
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在`org.springframework.context.annotation.AnnotationConfigApplicationContext#AnnotationConfigApplicationContext()`方法中，初始化`AnnotationConfigApplicationContext`实例中的两个关键组件：`AnnotatedBeanDefinitionReader`和`ClassPathBeanDefinitionScanner`，这两者分别用于处理注解式Bean定义和类路径扫描注册Bean定义。
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```java
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public AnnotationConfigApplicationContext() {
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StartupStep createAnnotatedBeanDefReader = this.getApplicationStartup().start("spring.context.annotated-bean-reader.create");
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this.reader = new AnnotatedBeanDefinitionReader(this);
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createAnnotatedBeanDefReader.end();
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this.scanner = new ClassPathBeanDefinitionScanner(this);
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}
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```
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在`org.springframework.context.annotation.AnnotationConfigApplicationContext#register`方法中，主要作用是通过`AnnotatedBeanDefinitionReader`注册一组组件类，将它们解析为Spring容器中的Bean定义。
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> **`this.reader.register(componentClasses)`方法的源码分析已经在另外一篇关于[AnnotatedBeanDefinitionReader](https://github.com/xuchengsheng/spring-reading/blob/master/spring-beans/spring-bean-annotatedBeanDefinitionReader/README.md)类的博客中详细分析了。**
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```java
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@Override
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public void register(Class<?>... componentClasses) {
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Assert.notEmpty(componentClasses, "At least one component class must be specified");
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StartupStep registerComponentClass = this.getApplicationStartup().start("spring.context.component-classes.register")
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.tag("classes", () -> Arrays.toString(componentClasses));
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this.reader.register(componentClasses);
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registerComponentClass.end();
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}
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```
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在`org.springframework.context.annotation.AnnotationConfigApplicationContext#scan`方法中，主要作用是通过`ClassPathBeanDefinitionScanner`扫描指定的基础包路径下的类，将它们解析为Spring容器中的Bean定义。
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> **`this.scanner.scan(basePackages)`方法的源码分析已经在另外一篇关于[ClassPathBeanDefinitionScanner](https://github.com/xuchengsheng/spring-reading/blob/master/spring-beans/spring-bean-classPathBeanDefinitionScanner/README.md)类的博客中详细分析了。**
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```java
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@Override
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public void scan(String... basePackages) {
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Assert.notEmpty(basePackages, "At least one base package must be specified");
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StartupStep scanPackages = this.getApplicationStartup().start("spring.context.base-packages.scan")
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.tag("packages", () -> Arrays.toString(basePackages));
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this.scanner.scan(basePackages);
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scanPackages.end();
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}
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```
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