Spring源码之@Configuration
@Configuration注解提供了全新的bean创建方式。最初spring通过xml配置文件初始化bean并完成依赖注入工作。从spring3.0开始，在spring framework模块中提供了这个注解，搭配@Bean等注解，可以完全不依赖xml配置，在运行时完成bean的创建和初始化工作。例如：
public interface IBean {
}
public class AppBean implements IBean{
}
// @Configuration申明了AppConfig是一个配置类
@Configuration
// 显式扫描需使用组件
@ComponentScan("xxx.xxx")
public class AppConfig {
// @Bean注解申明了一个bean，bean名称默认为方法名appBean
// 默认情况下bean的名称和方法名称相同
@Bean
IBean appBean(){
return new AppBean();
}
}@Configuration注解使用
Configuration.java
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
// @Component元注解，因此可以被@ComponentScan扫描并处理
@Component
public @interface Configuration {
@AliasFor(annotation = Component.class)
String value() default "";
}在这里认识几个注解: @Controller, @Service, @Repository, @Component
- @Controller: 表明一个注解的类是一个"Controller"，也就是控制器，可以把它理解为MVC 模式的Controller 这个角色。这个注解是一个特殊的@Component，允许实现类通过类路径的扫描扫描到。它通常与@RequestMapping 注解一起使用。
- @Service: 表明这个带注解的类是一个"Service"，也就是服务层，可以把它理解为MVC 模式中的Service层这个角色，这个注解也是一个特殊的@Component，允许实现类通过类路径的扫描扫描到
- @Repository: 表明这个注解的类是一个"Repository",团队实现了JavaEE 模式中像是作为"Data Access Object" 可能作为DAO来使用，当与 PersistenceExceptionTranslationPostProcessor 结合使用时，这样注释的类有资格获得Spring转换的目的。这个注解也是@Component 的一个特殊实现，允许实现类能够被自动扫描到
- @Component: 表明这个注释的类是一个组件，当使用基于注释的配置和类路径扫描时，这些类被视为自动检测的候选者。
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Controller {
@AliasFor(annotation = Component.class)
String value() default "";
}
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Service {
@AliasFor(annotation = Component.class)
String value() default "";
}
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Repository {
@AliasFor(annotation = Component.class)
String value() default "";
}我们可以看到@Controller, @Service, @Repository这三个注解上都有@Component这个注解
也就是说，上面四个注解标记的类都能够通过@ComponentScan 扫描到，上面四个注解最大的区别就是使用的场景和语义不一样，比如你定义一个Service类想要被Spring进行管理，你应该把它定义为@Service 而不是@Controller因为我们从语义上讲，@Service更像是一个服务的类，而不是一个控制器的类，@Component通常被称作组件，它可以标注任何你没有严格予以说明的类，比如说是一个配置类，它不属于MVC模式的任何一层，这个时候你更习惯于把它定义为 @Component。@Controller，@Service，@Repository 的注解上都有@Component，所以这三个注解都可以用@Component进行替换。
配置类约束
- 配置类必须为显式申明的类，而不能通过工厂类方法返回实例。允许运行时类增强。
- 配置类不允许标记final。
- 配置类必须全局可见（不允许定义在方法本地内部类中）
- 嵌套配置类必须申明为static 内部类
- @Bean方法不可以再创建新的配置类（所有实例都当做bean处理，不解析相关配置注解）
@Configuration源码
ApplicationContext的refresh方法
Spring容器启动时，即ApplicationContext接口实现类的对象实例执行refresh方法时，在Bean初始化完成之前，有一个扩展点，用来操作BeanFactory，来扩展对应的功能，比如往BeanFactory中注册BeanDefintion：
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
//准备刷新的上下文 环境
prepareRefresh();
//初始化BeanFactory，并进行XML文件读取
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
//对beanFactory进行各种功能填充
prepareBeanFactory(beanFactory);
try {
postProcessBeanFactory(beanFactory);
//激活各种beanFactory处理器
invokeBeanFactoryPostProcessors(beanFactory);
//注册拦截Bean创建的Bean处理器，这里只是注册，真正的调用实在getBean时候
registerBeanPostProcessors(beanFactory);
//为上下文初始化Message源，即不同语言的消息体，国际化处理
initMessageSource();
//初始化应用消息广播器，并放入“applicationEventMulticaster”bean中
initApplicationEventMulticaster();
//留给子类来初始化其它的Bean
onRefresh();
//在所有注册的bean中查找Listener bean，注册到消息广播器中
registerListeners();
//初始化剩下的单实例（非惰性的）
finishBeanFactoryInitialization(beanFactory);
//完成刷新过程，通知生命周期处理器lifecycleProcessor刷新过程，同时发出ContextRefreshEvent通知别人
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
destroyBeans();
cancelRefresh(ex);
throw ex;
}
finally {
resetCommonCaches();
}
}
}invokeBeanFactoryPostProcessors:
public static void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// Invoke BeanDefinitionRegistryPostProcessors first, if any.
// 1、首先调用BeanDefinitionRegistryPostProcessors
Set<String> processedBeans = new HashSet<>();
// beanFactory是BeanDefinitionRegistry类型
if (beanFactory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
// 定义BeanFactoryPostProcessor
List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
// 定义BeanDefinitionRegistryPostProcessor集合
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
// 循环手动注册的beanFactoryPostProcessors
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
// 如果是BeanDefinitionRegistryPostProcessor的实例话,则调用其postProcessBeanDefinitionRegistry方法,对bean进行注册操作
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
// 如果是BeanDefinitionRegistryPostProcessor类型,则直接调用其postProcessBeanDefinitionRegistry
BeanDefinitionRegistryPostProcessor registryProcessor = (BeanDefinitionRegistryPostProcessor) postProcessor;
registryProcessor.postProcessBeanDefinitionRegistry(registry);
registryProcessors.add(registryProcessor);
}
// 否则则将其当做普通的BeanFactoryPostProcessor处理,直接加入regularPostProcessors集合,以备后续处理
else {
regularPostProcessors.add(postProcessor);
}
}
//略....
}
// 2、如果不是BeanDefinitionRegistry的实例,那么直接调用其回调函数即可-->postProcessBeanFactory
else {
// Invoke factory processors registered with the context instance.
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
}
//略....
}而ConfigurationClassPostProcessor.java
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
//生成唯一标识，用于重复处理验证
int registryId = System.identityHashCode(registry);
if (this.registriesPostProcessed.contains(registryId)) {
throw new IllegalStateException(
"postProcessBeanDefinitionRegistry already called on this post-processor against " + registry);
}
if (this.factoriesPostProcessed.contains(registryId)) {
throw new IllegalStateException(
"postProcessBeanFactory already called on this post-processor against " + registry);
}
this.registriesPostProcessed.add(registryId);
//解析Java类配置bean
processConfigBeanDefinitions(registry);
}processConfigBeanDefinitions(registry):
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
//所有已经注册的bean
String[] candidateNames = registry.getBeanDefinitionNames();
//遍历bean定义信息
for (String beanName : candidateNames) {
BeanDefinition beanDef = registry.getBeanDefinition(beanName);
if (ConfigurationClassUtils.isFullConfigurationClass(beanDef) ||
ConfigurationClassUtils.isLiteConfigurationClass(beanDef)) {
if (logger.isDebugEnabled()) {
logger.debug("Bean definition has already been processed as a configuration class: " + beanDef);
}
}
//1.如果当前的bean是Javabean配置类（含有@Configuration注解的类），则加入到集合configCandidates中，
else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
}
}
// Return immediately if no @Configuration classes were found
// 没有@Configuration注解的类，直接退出
if (configCandidates.isEmpty()) {
return;
}
// 多个Java配置类，按@Ordered注解排序
configCandidates.sort((bd1, bd2) -> {
int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());
int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());
return Integer.compare(i1, i2);
});
// Detect any custom bean name generation strategy supplied through the enclosing application context
SingletonBeanRegistry sbr = null;
if (registry instanceof SingletonBeanRegistry) {
sbr = (SingletonBeanRegistry) registry;
if (!this.localBeanNameGeneratorSet) {
BeanNameGenerator generator = (BeanNameGenerator) sbr.getSingleton(CONFIGURATION_BEAN_NAME_GENERATOR);
if (generator != null) {
this.componentScanBeanNameGenerator = generator;
this.importBeanNameGenerator = generator;
}
}
}
if (this.environment == null) {
this.environment = new StandardEnvironment();
}
// Parse each @Configuration class
//初始化一个ConfigurationClassParser解析器，可以解析@Congiguration配置类
ConfigurationClassParser parser = new ConfigurationClassParser(
this.metadataReaderFactory, this.problemReporter, this.environment,
this.resourceLoader, this.componentScanBeanNameGenerator, registry);
Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);
Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());
do {
//2.解析Java配置类
parser.parse(candidates);
//主要校验配置类不能使用final修饰符（CGLIB代理是生成一个子类，因此原先的类不能使用final修饰）
parser.validate();
//排除已处理过的配置类
Set<ConfigurationClass> configClasses = new LinkedHashSet<>(parser.getConfigurationClasses());
configClasses.removeAll(alreadyParsed);
// Read the model and create bean definitions based on its content
if (this.reader == null) {
this.reader = new ConfigurationClassBeanDefinitionReader(
registry, this.sourceExtractor, this.resourceLoader, this.environment,
this.importBeanNameGenerator, parser.getImportRegistry());
}
//3.加载bean定义信息，主要实现将@bean @Configuration @Import @ImportResource @ImportRegistrar注册为bean
this.reader.loadBeanDefinitions(configClasses);
alreadyParsed.addAll(configClasses);
//清空已处理的配置类
candidates.clear();
//再次获取容器中bean定义数量 如果大于 之前获取的bean定义数量，则说明有新的bean注册到容器中，需要再次解析
if (registry.getBeanDefinitionCount() > candidateNames.length) {
String[] newCandidateNames = registry.getBeanDefinitionNames();
Set<String> oldCandidateNames = new HashSet<>(Arrays.asList(candidateNames));
Set<String> alreadyParsedClasses = new HashSet<>();
for (ConfigurationClass configurationClass : alreadyParsed) {
alreadyParsedClasses.add(configurationClass.getMetadata().getClassName());
}
for (String candidateName : newCandidateNames) {
if (!oldCandidateNames.contains(candidateName)) {
BeanDefinition bd = registry.getBeanDefinition(candidateName);
//新注册的bean如果也是@Configuration配置类,则添加到数据，等待解析
if (ConfigurationClassUtils.checkConfigurationClassCandidate(bd, this.metadataReaderFactory) &&
!alreadyParsedClasses.contains(bd.getBeanClassName())) {
candidates.add(new BeanDefinitionHolder(bd, candidateName));
}
}
}
candidateNames = newCandidateNames;
}
}
while (!candidates.isEmpty());
// Register the ImportRegistry as a bean in order to support ImportAware @Configuration classes
if (sbr != null && !sbr.containsSingleton(IMPORT_REGISTRY_BEAN_NAME)) {
sbr.registerSingleton(IMPORT_REGISTRY_BEAN_NAME, parser.getImportRegistry());
}
if (this.metadataReaderFactory instanceof CachingMetadataReaderFactory) {
// Clear cache in externally provided MetadataReaderFactory; this is a no-op
// for a shared cache since it'll be cleared by the ApplicationContext.
((CachingMetadataReaderFactory) this.metadataReaderFactory).clearCache();
}
}processConfigBeanDefinitions整个方法可以大体划分为三个阶段：
- 从容器中获取和Configuration有关系的BeanDefinition
- 以该BeanDefinition为起点，进行解析操作，得到解析结果集
- 将解析到的结果集加载到容器中，即构造成一个BeanDefinition放到容器中待初始化
ConfigurationClassUtils.checkConfigurationClassCandidate判断类是否与@Configuration有关
public static boolean checkConfigurationClassCandidate(BeanDefinition beanDef, MetadataReaderFactory metadataReaderFactory) {
String className = beanDef.getBeanClassName();
if (className == null || beanDef.getFactoryMethodName() != null) {
return false;
}
//获取注解元数据信息
AnnotationMetadata metadata;
if (beanDef instanceof AnnotatedBeanDefinition &&
className.equals(((AnnotatedBeanDefinition) beanDef).getMetadata().getClassName())) {
metadata = ((AnnotatedBeanDefinition) beanDef).getMetadata();
}
else if (beanDef instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) beanDef).hasBeanClass()) {
Class<?> beanClass = ((AbstractBeanDefinition) beanDef).getBeanClass();
metadata = new StandardAnnotationMetadata(beanClass, true);
}
else {
try {
MetadataReader metadataReader = metadataReaderFactory.getMetadataReader(className);
metadata = metadataReader.getAnnotationMetadata();
}
catch (IOException ex) {
return false;
}
}
// 查找当前注解是否是与@Configuration相关
// 该方法还会判断该注解上的注解是否有@Configuration，一直往上寻找
// 因为有的注解为复合注解
if (isFullConfigurationCandidate(metadata)) {
beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_FULL);
}
// 查找当前注解上是否有ComponentScan、Component、Import、ImportResource注解
//如果没有则查找Bean注解，同上，一直往上查找
else if (isLiteConfigurationCandidate(metadata)) {
beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_LITE);
}
else {
return false;
}
return true;
}isFullConfigurationCandidate
public static boolean isFullConfigurationCandidate(AnnotationMetadata metadata) {
return metadata.isAnnotated(Configuration.class.getName());
}isLiteConfigurationCandidate
public static boolean isLiteConfigurationCandidate(AnnotationMetadata metadata) {
// Do not consider an interface or an annotation...
if (metadata.isInterface()) {
return false;
}
// Any of the typical annotations found?
for (String indicator : candidateIndicators) {
if (metadata.isAnnotated(indicator)) {
return true;
}
}
// Finally, let's look for @Bean methods...
try {
return metadata.hasAnnotatedMethods(Bean.class.getName());
}
catch (Throwable ex) {
if (logger.isDebugEnabled()) {
logger.debug("Failed to introspect @Bean methods on class [" + metadata.getClassName() + "]: " + ex);
}
return false;
}
}
private static final Set<String> candidateIndicators = new HashSet<>(8);
static {
candidateIndicators.add(Component.class.getName());
candidateIndicators.add(ComponentScan.class.getName());
candidateIndicators.add(Import.class.getName());
candidateIndicators.add(ImportResource.class.getName());
}解析Java配置类parser.parse(candidates)
parser.parse(candidates)方法最终调用processConfigurationClass方法来处理@Configuration配置类，ConfigurationClassParser. processConfigurationClass()方法实现代码如下
protected void processConfigurationClass(ConfigurationClass configClass) throws IOException {
//判断是否需要解析
if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) {
return;
}
//判断同一个配置类是否重复加载过，如果重复加载过，则合并，否则从集合中移除旧的配置类，后续逻辑将处理新的配置类
ConfigurationClass existingClass = this.configurationClasses.get(configClass);
if (existingClass != null) {
if (configClass.isImported()) {
if (existingClass.isImported()) {
existingClass.mergeImportedBy(configClass);
}
// Otherwise ignore new imported config class; existing non-imported class overrides it.
return;
}
else {
// Explicit bean definition found, probably replacing an import.
// Let's remove the old one and go with the new one.
this.configurationClasses.remove(configClass);
this.knownSuperclasses.values().removeIf(configClass::equals);
}
}
// Recursively process the configuration class and its superclass hierarchy.
SourceClass sourceClass = asSourceClass(configClass);
do {
//【真正解析配置类】
sourceClass = doProcessConfigurationClass(configClass, sourceClass);
}
while (sourceClass != null);
//再次添加到到集合中
this.configurationClasses.put(configClass, configClass);
}doProcessConfigurationClass方法主要实现从配置类中解析所有bean，包括处理内部类，父类以及各种注解
ConfigurationClassParser. doProcessConfigurationClass()解析配置类逻辑如下：
@Nullable
protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
throws IOException {
if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
// Recursively process any member (nested) classes first
//递归处理任何成员（嵌套）类
processMemberClasses(configClass, sourceClass);
}
// Process any @PropertySource annotations
// 处理@PropertySource注解
for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
sourceClass.getMetadata(), PropertySources.class,
org.springframework.context.annotation.PropertySource.class)) {
if (this.environment instanceof ConfigurableEnvironment) {
processPropertySource(propertySource);
}
else {
logger.info("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
"]. Reason: Environment must implement ConfigurableEnvironment");
}
}
// 处理@ComponentScan
// 获取@ComponentScan注解信息
Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(
sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);
if (!componentScans.isEmpty() &&
!this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {
for (AnnotationAttributes componentScan : componentScans) {
// The config class is annotated with @ComponentScan -> perform the scan immediately
// 按@CmponentScan注解扫描bean
Set<BeanDefinitionHolder> scannedBeanDefinitions =
this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
// Check the set of scanned definitions for any further config classes and parse recursively if needed
// 遍历扫描出的bean定义是否是配置类bean
for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
if (bdCand == null) {
bdCand = holder.getBeanDefinition();
}
//若果扫描出的bean定义是配置类（含有@COnfiguration）,则继续调用parse方法，内部再次调用doProcessConfigurationClas(),递归解析
if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
parse(bdCand.getBeanClassName(), holder.getBeanName());
}
}
}
}
// Process any @Import annotations
processImports(configClass, sourceClass, getImports(sourceClass), true);
// Process any @ImportResource annotations
AnnotationAttributes importResource =
AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
if (importResource != null) {
String[] resources = importResource.getStringArray("locations");
Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");
for (String resource : resources) {
String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);
configClass.addImportedResource(resolvedResource, readerClass);
}
}
// Process individual @Bean methods
Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}
// Process default methods on interfaces
processInterfaces(configClass, sourceClass);
// Process superclass, if any
if (sourceClass.getMetadata().hasSuperClass()) {
String superclass = sourceClass.getMetadata().getSuperClassName();
if (superclass != null && !superclass.startsWith("java") &&
!this.knownSuperclasses.containsKey(superclass)) {
this.knownSuperclasses.put(superclass, configClass);
// Superclass found, return its annotation metadata and recurse
return sourceClass.getSuperClass();
}
}
// No superclass -> processing is complete
return null;
}@ComponentScan
@ComponentScan注解解析过程
Set<BeanDefinitionHolder> scannedBeanDefinitions =
this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());@ComponentScan注解解析，从上面的代码可以看出@ComponentScan注解解析通过调用ComponentScanAnnotationParser的parse方法完成，而parse()方法内部处理了一些scanner属性(过滤器设置)和basePackages包名处理，最终通过调用ClassPathBeanDefinitionScanner.doScan方法实现扫面工作
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) {
//根据basePackage加载包下所有java文件，并扫描出所有bean组件
Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
//遍历beandefition
for (BeanDefinition candidate : candidates) {
//解析作用域Scope
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);
}
//通用注解解析到candidate结构中，主要是处理Lazy, primary, DependsOn, Role ,Description这五个注解
if (candidate instanceof AnnotatedBeanDefinition) {
AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
}
//检查当前bean是否已经注册，不存在则注册
if (checkCandidate(beanName, candidate)) {
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
definitionHolder =
AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
beanDefinitions.add(definitionHolder);
// 注册到ioc容器中，主要是一些@Component组件，@Bean注解方法并没有在此处注册，beanname和beandefinition 键值对
registerBeanDefinition(definitionHolder, this.registry);
}
}
}
return beanDefinitions;
}而bean定义信息扫描Set<BeanDefinition> candidates = findCandidateComponents(basePackage);最终调用的是ClassPathScanningCandidateComponentProvider.scanCandidateComponents
private Set<BeanDefinition> scanCandidateComponents(String basePackage) {
Set<BeanDefinition> candidates = new LinkedHashSet<>();
try {
// @ComponentScan("com.gyt.study")包路径处理：packageSearchPath = classpath*:com/gyt/study/**/*.class
String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
resolveBasePackage(basePackage) + '/' + this.resourcePattern;
// //获取当前包下所有的class文件
Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath);
boolean traceEnabled = logger.isTraceEnabled();
boolean debugEnabled = logger.isDebugEnabled();
for (Resource resource : resources) {
if (traceEnabled) {
logger.trace("Scanning " + resource);
}
if (resource.isReadable()) {
try {
MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(resource);
//按照scanner过滤器过滤，比如配置类本身将被过滤掉，没有@Component等组件注解的类将过滤掉
//包含@Component注解的组件将创建BeanDefinition
if (isCandidateComponent(metadataReader)) {
ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
sbd.setSource(resource);
if (isCandidateComponent(sbd)) {
if (debugEnabled) {
logger.debug("Identified candidate component class: " + resource);
}
candidates.add(sbd);
}
else {
if (debugEnabled) {
logger.debug("Ignored because not a concrete top-level class: " + resource);
}
}
}
else {
if (traceEnabled) {
logger.trace("Ignored because not matching any filter: " + resource);
}
}
}
catch (Throwable ex) {
throw new BeanDefinitionStoreException(
"Failed to read candidate component class: " + resource, ex);
}
}
else {
if (traceEnabled) {
logger.trace("Ignored because not readable: " + resource);
}
}
}
}
catch (IOException ex) {
throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);
}
return candidates;
}@Bean
Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);方法实现了@Bean方法的解析，但并未将实现bean实例的创建。
private Set<MethodMetadata> retrieveBeanMethodMetadata(SourceClass sourceClass) {
AnnotationMetadata original = sourceClass.getMetadata();
//获取所有@Bean注解的方法
Set<MethodMetadata> beanMethods = original.getAnnotatedMethods(Bean.class.getName());
// 如果配置类中有多个@Bean注解的方法，则排序
if (beanMethods.size() > 1 && original instanceof StandardAnnotationMetadata) {
// Try reading the class file via ASM for deterministic declaration order...
// Unfortunately, the JVM's standard reflection returns methods in arbitrary
// order, even between different runs of the same application on the same JVM.
try {
AnnotationMetadata asm =
this.metadataReaderFactory.getMetadataReader(original.getClassName()).getAnnotationMetadata();
Set<MethodMetadata> asmMethods = asm.getAnnotatedMethods(Bean.class.getName());
if (asmMethods.size() >= beanMethods.size()) {
Set<MethodMetadata> selectedMethods = new LinkedHashSet<>(asmMethods.size());
for (MethodMetadata asmMethod : asmMethods) {
for (MethodMetadata beanMethod : beanMethods) {
if (beanMethod.getMethodName().equals(asmMethod.getMethodName())) {
selectedMethods.add(beanMethod);
break;
}
}
}
if (selectedMethods.size() == beanMethods.size()) {
// All reflection-detected methods found in ASM method set -> proceed
beanMethods = selectedMethods;
}
}
}
catch (IOException ex) {
logger.debug("Failed to read class file via ASM for determining @Bean method order", ex);
// No worries, let's continue with the reflection metadata we started with...
}
}
return beanMethods;
}回到ConfigurationClassPostProcessor#processConfigBeanDefinitions方法，当调用完parse方法之后，能得到一批ConfigurationClass集合，但是这时候只是获取到，而容器中还没有对应的注册信息，那么接下来就是对这批集合进行注册处理
ConfigurationClassBeanDefinitionReader.loadBeanDefinitions()方法的功能就是将之前解析出的configClasses配置类信息中所有配置相关的信息添加到spring的bean定义，主要是配置类中的@Bean注解方法，配置类@ImportResource和@Import(实现ImportBeanDefinitionRegistrar接口方式)的bean注册
ConfigurationClassBeanDefinitionReader.loadBeanDefinitions()方法 实现逻辑如下：
/**
* Read {@code configurationModel}, registering bean definitions
* with the registry based on its contents.
*/
public void loadBeanDefinitions(Set<ConfigurationClass> configurationModel) {
TrackedConditionEvaluator trackedConditionEvaluator = new TrackedConditionEvaluator();
for (ConfigurationClass configClass : configurationModel) {
loadBeanDefinitionsForConfigurationClass(configClass, trackedConditionEvaluator);
}
} /**
* Read a particular {@link ConfigurationClass}, registering bean definitions
* for the class itself and all of its {@link Bean} methods.
*/
private void loadBeanDefinitionsForConfigurationClass(
ConfigurationClass configClass, TrackedConditionEvaluator trackedConditionEvaluator) {
if (trackedConditionEvaluator.shouldSkip(configClass)) {
String beanName = configClass.getBeanName();
if (StringUtils.hasLength(beanName) && this.registry.containsBeanDefinition(beanName)) {
this.registry.removeBeanDefinition(beanName);
}
this.importRegistry.removeImportingClass(configClass.getMetadata().getClassName());
return;
}
//与@Import注解相关
if (configClass.isImported()) {
registerBeanDefinitionForImportedConfigurationClass(configClass);
}
//将@Bean方法注册为bean
for (BeanMethod beanMethod : configClass.getBeanMethods()) {
loadBeanDefinitionsForBeanMethod(beanMethod);
}
loadBeanDefinitionsFromImportedResources(configClass.getImportedResources());
loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars());
}loadBeanDefinitionsForBeanMethod
private void loadBeanDefinitionsForBeanMethod(BeanMethod beanMethod) {
ConfigurationClass configClass = beanMethod.getConfigurationClass();
MethodMetadata metadata = beanMethod.getMetadata();
//获取方法名
String methodName = metadata.getMethodName();
// Do we need to mark the bean as skipped by its condition?
if (this.conditionEvaluator.shouldSkip(metadata, ConfigurationPhase.REGISTER_BEAN)) {
configClass.skippedBeanMethods.add(methodName);
return;
}
if (configClass.skippedBeanMethods.contains(methodName)) {
return;
}
//获取@Bean注解的元数据信息
AnnotationAttributes bean = AnnotationConfigUtils.attributesFor(metadata, Bean.class);
Assert.state(bean != null, "No @Bean annotation attributes");
// Consider name and any aliases
//获取@Bean注解是否有name属性，如@Bean(name = "myBean")
List<String> names = new ArrayList<>(Arrays.asList(bean.getStringArray("name")));
//默认bean的名称和方法名称相同,但是如果设置了name，就取name作为beanName
String beanName = (!names.isEmpty() ? names.remove(0) : methodName);
//创建一个BeanMethod的BeanDefinition
ConfigurationClassBeanDefinition beanDef = new ConfigurationClassBeanDefinition(configClass, metadata);
beanDef.setResource(configClass.getResource());
beanDef.setSource(this.sourceExtractor.extractSource(metadata, configClass.getResource()));
//设置工厂方法
//后期Bean的实例化，getBean的时候，会判断BeanMethod是否存在FactoryMethod，如果存在，就使用反射调用工厂方法，返回工厂方法中的对象
if (metadata.isStatic()) {
// static @Bean method
beanDef.setBeanClassName(configClass.getMetadata().getClassName());
beanDef.setFactoryMethodName(methodName);
}
else {
// instance @Bean method
beanDef.setFactoryBeanName(configClass.getBeanName());
beanDef.setUniqueFactoryMethodName(methodName);
}
//....
this.registry.registerBeanDefinition(beanName, beanDefToRegister);
}Component注解的派生性原理
https://www.cnblogs.com/liuen...
模式注解
Stereotype Annotation俗称为模式注解。Spring核心部分提供了几种内建的模式注解,如@Component,@Repository,@Service,@Controller,@Configuration等。这些注解均派生于@Component。
由于Java语言规定,Annotation不允许继承,没有类派生子类的特性,因此Spring采用元标注的方式实现注解之间的派生。
@Component派生性
@Component注解作为Spring容器托管的通用模式组件,任何被@Component标注的组件均为组件扫描的候选对象。
当ClassPathBeanDefinitionScanner#doScan(String... basePackages)调用时,它利用basePackages参数迭代执行的findCandidateComponents(String basePackage),每次执行结果都生成候选的BeanDefinition集合,即candidates变量。
源码如上
默认情况下,ClassPathScanningCandidateComponentProvider构造参数useDefaultFilters为true,并且显示传递给父类构造参数。该方法给属性includeFilters增添了@Component类型AnnotationTypeFilter的TypeFilter。
registerDefaultFilters
protected void registerDefaultFilters() {
this.includeFilters.add(new AnnotationTypeFilter(Component.class));
ClassLoader cl = ClassPathScanningCandidateComponentProvider.class.getClassLoader();
try {
this.includeFilters.add(new AnnotationTypeFilter(
((Class<? extends Annotation>) ClassUtils.forName("javax.annotation.ManagedBean", cl)), false));
logger.trace("JSR-250 'javax.annotation.ManagedBean' found and supported for component scanning");
}
catch (ClassNotFoundException ex) {
// JSR-250 1.1 API (as included in Java EE 6) not available - simply skip.
}
try {
this.includeFilters.add(new AnnotationTypeFilter(
((Class<? extends Annotation>) ClassUtils.forName("javax.inject.Named", cl)), false));
logger.trace("JSR-330 'javax.inject.Named' annotation found and supported for component scanning");
}
catch (ClassNotFoundException ex) {
// JSR-330 API not available - simply skip.
}
}ClassPathBeanDefinitionScanner默认过滤器引入标注@Component,@Repository,@Service或者@Controller等类。同理,它也能够标注所有@Component的"派生"注解。
扩展
利用ClassPathBeanDefinitionScanner类配合includeFilters和excludeFilters定制化批量注册Bean到Spring容器中。常常可以通过注解方式来包含或者排除候选类。
TypeFilter常用实现
- AnnotationTypeFilter:注解类型过滤器
- AssignableTypeFilter:确定此对象表示的类或者接口是否为给定类或者接口相同。
- RegexPatternTypeFilter:判断给定的类名是否符合指定正则表达式。
@AliasFor
@AliasFor 用法：
* 用到注解 属性上，表示两个属性互相为别名，互相为别名的属性值必须相同，若设置成不同，则会报错
* 注解是可以继承的，但是注解是不能继承父注解的属性的,也就是说,我在类扫描的时候,拿到的注解的属性值,依然是父注解的属性值,而不是你定义的注解的属性值
* 所以此时可以在子注解对应的属性上加上@AliasFor
* 总结
处理逻辑理了一遍后，看一下ConfigurationClassPostProcessor处理器解析@configuration配置类主要过程：
1. Spring容器初始化时注册默认后置处理器ConfigurationClassPostProcessor
2. Spring容器初始化执行refresh()方法中调用ConfigurationClassPostProcessor
3. ConfigurationClassPostProcessor处理器借助ConfigurationClassParser完成配置类解析
4. ConfigurationClassParser配置内解析过程中完成嵌套的MemberClass、@PropertySource注解、@ComponentScan注解（扫描package下的所有Class并进行迭代解析，主要是@Component组件解析及注册）、@ImportResource、@Bean等处理
5. 完成@Bean注册， @ImportResource指定bean的注册以及@Import(实现ImportBeanDefinitionRegistrar接口方式)的bean注册
6.有@Bean注解的方法在解析的时候作为ConfigurationClass的一个属性，最后还是会转换成BeanDefinition进行处理， 而实例化的时候会作为一个工厂方法进行Bean的创建
java
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