本文详细描述了Spring框架中的ComponentScan注解解析器的工作原理，包括如何根据配置扫描指定类、使用默认过滤器、自定义扫描规则以及处理Bean的初始化和依赖关系。
private final ComponentScanAnnotationParser componentScanParser ;
// 实际上 registry = ConfigurableListableBeanFactory
// resourceLoader = new DefaultResourceLoader();
// componentScanBeanNameGenerator = new AnnotationBeanNameGenerator();
// environment = new StandardEnvironment();
this.componentScanParser = new ComponentScanAnnotationParser(Environment environment, ResourceLoader resourceLoader,BeanNameGenerator componentScanBeanNameGenerator,BeanDefinitionRegistry registry);
// 解析配置declaringClass配置类信息,ComponentScan注解信息
public Set<BeanDefinitionHolder> parse(AnnotationAttributes componentScan, final String declaringClass) {
// 创建类路径下的BD的扫描器
ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(this.registry,componentScan.getBoolean("useDefaultFilters"), this.environment, this.resourceLoader);{
this.registry = registry;
// 是否使用默认的扫描过滤器,默认为true
if (useDefaultFilters) {
// 添加默认的filter
registerDefaultFilters();{
// 扫描@Component
this.includeFilters.add(new AnnotationTypeFilter(Component.class));
// 扫描JSR的@ManagedBean注解
this.includeFilters.add(new AnnotationTypeFilter(((Class<? extends Annotation>) ClassUtils.forName("javax.annotation.ManagedBean", cl)), false));
// 扫描JSR中,@Named的类
this.includeFilters.add(new AnnotationTypeFilter(((Class<? extends Annotation>) ClassUtils.forName("javax.inject.Named", cl))
}
}
// 设置环境对象
setEnvironment(environment);
// 设置资源加载器
setResourceLoader(resourceLoader);
}
// 获取componentScan注解中的属性
Class<? extends BeanNameGenerator> generatorClass = componentScan.getClass("nameGenerator");
// 设置BeanName的生成器
boolean useInheritedGenerator = (BeanNameGenerator.class == generatorClass);
scanner.setBeanNameGenerator(useInheritedGenerator ? this.beanNameGenerator : BeanUtils.instantiateClass(generatorClass));
// 设置Scoped的代理模式
ScopedProxyMode scopedProxyMode = componentScan.getEnum("scopedProxy");
if (scopedProxyMode != ScopedProxyMode.DEFAULT) {
scanner.setScopedProxyMode(scopedProxyMode);
}
else {
// 设置作用域的解析器
Class<? extends ScopeMetadataResolver> resolverClass = componentScan.getClass("scopeResolver");
scanner.setScopeMetadataResolver(BeanUtils.instantiateClass(resolverClass));
}
// 设置资源扫描规则
scanner.setResourcePattern(componentScan.getString("resourcePattern"));
/// 获取需要添加的扫描过滤器
for (AnnotationAttributes filter : componentScan.getAnnotationArray("includeFilters")) {
for (TypeFilter typeFilter : typeFiltersFor(filter){
List<TypeFilter> typeFilters = new ArrayList<>();
FilterType filterType = filterAttributes.getEnum("type");
// 根据过滤类型来添加对应的过滤器
for (Class<?> filterClass : filterAttributes.getClassArray("classes")) {
switch (filterType) {
case ANNOTATION:
Class<Annotation> annotationType = (Class<Annotation>) filterClass;
typeFilters.add(new AnnotationTypeFilter(annotationType));
break;
case ASSIGNABLE_TYPE:
typeFilters.add(new AssignableTypeFilter(filterClass));
break;
case CUSTOM:
TypeFilter filter = ParserStrategyUtils.instantiateClass(filterClass, TypeFilter.class,
this.environment, this.resourceLoader, this.registry);
typeFilters.add(filter);
break;
default:
throw new IllegalArgumentException("Filter type not supported with Class value: " + filterType);
}
}
// 根据过滤规则来添加处理类
for (String expression : filterAttributes.getStringArray("pattern")) {
switch (filterType) {
case ASPECTJ:
typeFilters.add(new AspectJTypeFilter(expression, this.resourceLoader.getClassLoader()));
break;
case REGEX:
typeFilters.add(new RegexPatternTypeFilter(Pattern.compile(expression)));
break;
default:
throw new IllegalArgumentException("Filter type not supported with String pattern: " + filterType);
}
}
return typeFilters;
}) {
}
scanner.addIncludeFilter(typeFilter);
}
}
// 获取需要排除的扫描过滤器
for (AnnotationAttributes filter : componentScan.getAnnotationArray("excludeFilters")) {
for (TypeFilter typeFilter : typeFiltersFor(filter)) {
scanner.addExcludeFilter(typeFilter);
}
}
// 获取扫描的类是否是懒加载
boolean lazyInit = componentScan.getBoolean("lazyInit");
if (lazyInit) {
scanner.getBeanDefinitionDefaults().setLazyInit(true);
}
// 获取需要扫描的包路径
Set<String> basePackages = new LinkedHashSet<>();
String[] basePackagesArray = componentScan.getStringArray("basePackages");
for (String pkg : basePackagesArray) {
String[] tokenized = StringUtils.tokenizeToStringArray(this.environment.resolvePlaceholders(pkg),ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
Collections.addAll(basePackages, tokenized);
}
// 需要扫描的类,获取的是类对应的包名
for (Class<?> clazz : componentScan.getClassArray("basePackageClasses")) {
basePackages.add(ClassUtils.getPackageName(clazz));
}
// 如果没有配置basePackages,默认使用当前类的包名进行扫描
if (basePackages.isEmpty()) {
basePackages.add(ClassUtils.getPackageName(declaringClass));
}
// 添加排除过滤器,排除当前类传入的配置类
scanner.addExcludeFilter(new AbstractTypeHierarchyTraversingFilter(false, false) {
@Override
protected boolean matchClassName(String className) {
return declaringClass.equals(className);
}
});
// 开始扫描
return scanner.doScan(StringUtils.toStringArray(basePackages));{
Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
// 遍历所有需要扫描的包
for (String basePackage : basePackages) {
// 扫描所有的Bean
Set<BeanDefinition> candidates = findCandidateComponents(basePackage);{
// 存在索引文件COMPONENTS_RESOURCE_LOCATION,META-INF/spring.components文件
if (this.componentsIndex != null && indexSupportsIncludeFilters()) {
// 从spring.components加载给定Bean
return addCandidateComponentsFromIndex(this.componentsIndex, basePackage);{
Set<BeanDefinition> candidates = new LinkedHashSet<>();
Set<String> types = new HashSet<>();
for (TypeFilter filter : this.includeFilters) {
// 找到注解的类型
String stereotype = extractStereotype(filter);
if (stereotype == null) {
throw new IllegalArgumentException("Failed to extract stereotype from " + filter);
}
// 保存注解对应的多个类
types.addAll(index.getCandidateTypes(basePackage, stereotype));
}
// 遍历找到的类
for (String type : types) {
MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(type);
// 判断当前类被TypeFilter过滤之后,是否满足扫描条件
if (isCandidateComponent(metadataReader)) {
// 如果没有被过滤掉,是Bean,创建BD,保存起来
AnnotatedGenericBeanDefinition sbd = new AnnotatedGenericBeanDefinition(metadataReader.getAnnotationMetadata());
// 判断是否满足Bean的条件
if (isCandidateComponent(sbd){
AnnotationMetadata metadata = beanDefinition.getMetadata();
// 1. 当前类是独立的,例如静态内部类和独立类,其他类不满足
// 2. 当前类是否是具体的类,也就是非抽象类或者接口
// 3. 当前类是抽象类,但是这个抽象类中有Lookup注解,也可以当成Bean
return (metadata.isIndependent() && (metadata.isConcrete() ||
(metadata.isAbstract() && metadata.hasAnnotatedMethods(Lookup.class.getName()))));
}) {
}
candidates.add(sbd);
}
}
}
return candidates;
}
else {
// 否则扫描所有的Bean
return scanCandidateComponents(basePackage);{
Set<BeanDefinition> candidates = new LinkedHashSet<>();
// 搜索的路径 classpath*:扫描的包路径/**/*.class
String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX + resolveBasePackage(basePackage) + '/' + this.resourcePattern;
// 扫描路径上所有的类
Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath);
for (Resource resource : resources) {
if (resource.isReadable()) {
MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(resource);
// 判断当前类被TypeFilter过滤之后,是否满足扫描条件
if (isCandidateComponent(metadataReader)) {
ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
sbd.setResource(resource);
sbd.setSource(resource);
// 判断是否满足Bean的条件
// 1. 当前类是独立的,例如静态内部类和独立类,其他类不满足
// 2. 当前类是否是具体的类,也就是非抽象类或者接口
// 3. 当前类是抽象类,但是这个抽象类中有Lookup注解,也可以当成Bean
if (isCandidateComponent(sbd)) {
candidates.add(sbd);
}
}
}
}
return candidates;
}
}
}
// 遍历找到的所有BD
for (BeanDefinition candidate : candidates) {
// 设置Scope
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
candidate.setScope(scopeMetadata.getScopeName());
// 设置BeanName
String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
// 如果是BD类型(AbstractBeanDefinition),就执行默认值
if (candidate instanceof AbstractBeanDefinition) {
// 设置默认值
postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);{
// new BeanDefinitionDefaults();
beanDefinition.applyDefaults(this.beanDefinitionDefaults);{
Boolean lazyInit = defaults.getLazyInit();
if (lazyInit != null) {
setLazyInit(lazyInit);
}
setAutowireMode(defaults.getAutowireMode());
setDependencyCheck(defaults.getDependencyCheck());
setInitMethodName(defaults.getInitMethodName());
setEnforceInitMethod(false);
setDestroyMethodName(defaults.getDestroyMethodName());
setEnforceDestroyMethod(false);
}
if (this.autowireCandidatePatterns != null) {
beanDefinition.setAutowireCandidate(PatternMatchUtils.simpleMatch(this.autowireCandidatePatterns, beanName));
}
}
}
// 如果是注解的BD
if (candidate instanceof AnnotatedBeanDefinition) {
AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);{
// 设置BD相关注解信息
AnnotationAttributes lazy = attributesFor(metadata, Lazy.class);
if (lazy != null) {
abd.setLazyInit(lazy.getBoolean("value"));
}
else if (abd.getMetadata() != metadata) {
lazy = attributesFor(abd.getMetadata(), Lazy.class);
if (lazy != null) {
abd.setLazyInit(lazy.getBoolean("value"));
}
}
if (metadata.isAnnotated(Primary.class.getName())) {
abd.setPrimary(true);
}
AnnotationAttributes dependsOn = attributesFor(metadata, DependsOn.class);
if (dependsOn != null) {
abd.setDependsOn(dependsOn.getStringArray("value"));
}
AnnotationAttributes role = attributesFor(metadata, Role.class);
if (role != null) {
abd.setRole(role.getNumber("value").intValue());
}
AnnotationAttributes description = attributesFor(metadata, Description.class);
if (description != null) {
abd.setDescription(description.getString("value"));
}
}
}
// 去重,判断当前BeanName是否被扫描过,因为包路径可以设置多个,可能存在包含关系,一个类可以被扫描多次
if (checkCandidate(beanName, candidate)) {
// 如果没有重复,将BD包装成BeanDefinitionHolder
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
// 如果ScopedProxyMode为NO,表示当前BD不需要使用代理,否则需要使用代理
// 如果需要使用代理,则需要根据原来的BDH创建新的(代理)的BDH
// 这样到时候创建对象的时候,创建的可能是代理对象
definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
beanDefinitions.add(definitionHolder);
// 将BD注册到BeanDefinitionRegistry中
registerBeanDefinition(definitionHolder, this.registry);
}
}
}
return beanDefinitions;
}
}
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