spring 创建注解(@Service @Component 等)扫描器源码解析（三）

╰半夏微凉° 2023-10-07 12:51 11阅读 0赞

上一篇介绍spring 自定义扫描标签解析过程，中间有个重要的知识点我们单独取出来分析，就是注解扫描器的创建

1、ComponentScanBeanDefinitionParser implements BeanDefinitionParser 这里开始创建

@Override
    @Nullable
    public BeanDefinition parse(Element element, ParserContext parserContext) {
       //获取basePackage属性
       String basePackage = element.getAttribute(BASE_PACKAGE_ATTRIBUTE);
       basePackage = parserContext.getReaderContext().getEnvironment().resolvePlaceholders(basePackage);
       //可以用逗号分开
       String[] basePackages = StringUtils.tokenizeToStringArray(basePackage,
             ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
    
       //创建注解扫描器，今天从这里开始，点击进入
       ClassPathBeanDefinitionScanner scanner = configureScanner(parserContext, element);
       //扫描并把扫描的类封装成beanDefinition对象  核心方法，重要程度 5
       Set<BeanDefinitionHolder> beanDefinitions = scanner.doScan(basePackages);
       registerComponents(parserContext.getReaderContext(), beanDefinitions, element);
    
       return null;
    }

protected ClassPathBeanDefinitionScanner configureScanner(ParserContext parserContext, Element element) {
       //使用默认的过滤器
       boolean useDefaultFilters = true;
       //@Service @Component  默认filter
       if (element.hasAttribute(USE_DEFAULT_FILTERS_ATTRIBUTE)) {
          useDefaultFilters = Boolean.valueOf(element.getAttribute(USE_DEFAULT_FILTERS_ATTRIBUTE));
       }
    
       //从这里开始  创建注解的扫描器
       ClassPathBeanDefinitionScanner scanner = createScanner(parserContext.getReaderContext(), useDefaultFilters);
       scanner.setBeanDefinitionDefaults(parserContext.getDelegate().getBeanDefinitionDefaults());
       scanner.setAutowireCandidatePatterns(parserContext.getDelegate().getAutowireCandidatePatterns());
     //删除部分代码
       try {
          parseBeanNameGenerator(element, scanner);
       }
       try {
          parseScope(element, scanner);
       }
       parseTypeFilters(element, scanner, parserContext);
    
       return scanner;
    }

protected ClassPathBeanDefinitionScanner createScanner(XmlReaderContext readerContext, boolean useDefaultFilters) {
    //点击进入
       return new ClassPathBeanDefinitionScanner(readerContext.getRegistry(), useDefaultFilters,
             readerContext.getEnvironment(), readerContext.getResourceLoader());
    }

2、ClassPathBeanDefinitionScanner extends ClassPathScanningCandidateComponentProvider

public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters,
          Environment environment, @Nullable ResourceLoader resourceLoader) {
    
       Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
       this.registry = registry;
    
       //使用默认的过滤器
       if (useDefaultFilters) {
          //默认的 注解@Service @Component  点击进入
          registerDefaultFilters();
       }
       setEnvironment(environment);
       setResourceLoader(resourceLoader);
    }

3、 ClassPathScanningCandidateComponentProvider implements EnvironmentCapable, ResourceLoaderAware

protected void registerDefaultFilters() {
       //过滤器中添加需要扫描的注解类型，把componet 注解包装 同时也处理了@server注解，一样它继承了compont注解
       this.includeFilters.add(new AnnotationTypeFilter(Component.class));
       ClassLoader cl = ClassPathScanningCandidateComponentProvider.class.getClassLoader();
       //删除不重要的
    }

4、

@Target({ElementType.TYPE})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @org.springframework.stereotype.Component//继承了compont注解
    public @interface Service {
    
       /**
        * The value may indicate a suggestion for a logical component name,
        * to be turned into a Spring bean in case of an autodetected component.
        * @return the suggested component name, if any (or empty String otherwise)
        */
       @AliasFor(annotation = org.springframework.stereotype.Component.class)
       String value() default "";
    
    }

5、到这里大家应该豁然开朗了吧，项目中常用的注解 @Component @Service 在这里开始进入我们视线。下篇我们介绍类里面的注解问题，大家可以先思考一下。敬请期待！