1. 简介

@Controller、@Service、@Repository都继承了@Component的特性，所以它们能够被Spring容器扫描，放入容器中。如下以Controller注解源码为例

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Controller {

    /**
     * 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 = Component.class)
    String value() default "";

}

2. ClassPathScanningCandidateComponentProvider类

2.1 ClassPathBeanDefinitionScanner类

image.png

在指定的基本包中执行扫描，返回注册的bean定义。

    /**
     * Perform a scan within the specified base packages,
     * returning the registered bean definitions.
     * <p>This method does <i>not</i> register an annotation config processor
     * but rather leaves this up to the caller.
     * @param basePackages the packages to check for annotated classes
     * @return set of beans registered if any for tooling registration purposes (never {@code null})
     */
    protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
        Assert.notEmpty(basePackages, "At least one base package must be specified");
        Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
        for (String basePackage : basePackages) {
            Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
            for (BeanDefinition candidate : candidates) {
                ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
                candidate.setScope(scopeMetadata.getScopeName());
                String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
                if (candidate instanceof AbstractBeanDefinition) {
                    postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
                }
                if (candidate instanceof AnnotatedBeanDefinition) {
                    AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
                }
                if (checkCandidate(beanName, candidate)) {
                    BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
                    definitionHolder =
                            AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
                    beanDefinitions.add(definitionHolder);
                    registerBeanDefinition(definitionHolder, this.registry);
                }
            }
        }
        return beanDefinitions;
    }

2.2 AnnotationTypeFilter过滤器

这个过滤器在spring-core的包下

继承关系如下

image.png
2.3 ClassPathScanningCandidateComponentProvider类
确定给定的类是否与任何排除筛选器不匹配,并且至少匹配一个include过滤器

    /**
     * Determine whether the given class does not match any exclude filter
     * and does match at least one include filter.
     * @param metadataReader the ASM ClassReader for the class
     * @return whether the class qualifies as a candidate component
     */
    protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException {
        for (TypeFilter tf : this.excludeFilters) {
            if (tf.match(metadataReader, getMetadataReaderFactory())) {
                return false;
            }
        }
        for (TypeFilter tf : this.includeFilters) {
            if (tf.match(metadataReader, getMetadataReaderFactory())) {
                return isConditionMatch(metadataReader);
            }
        }
        return false;
    }

寻找组件

    /**
     * Scan the class path for candidate components.
     * @param basePackage the package to check for annotated classes
     * @return a corresponding Set of autodetected bean definitions
     */
    public Set<BeanDefinition> findCandidateComponents(String basePackage) {
        if (this.componentsIndex != null && indexSupportsIncludeFilters()) {
            return addCandidateComponentsFromIndex(this.componentsIndex, basePackage);
        }
        else {
            return scanCandidateComponents(basePackage);
        }
    }