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摘要: 原创出处 juejin.im/post/5efdd689e51d4534af686ca9 「温安适」欢迎转载,保留摘要,谢谢!


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工作中经常用到,如下注解:

  • @EnableEurekaClient
  • @EnableFeignClients
  • @EnableCircuitBreaker
  • @EnableHystrix

他们都是@Enable开头,各自实现不同的功能,解析这种@Enable的逻辑是什么呢?

@Enable驱动逻辑

找入口

@Enable的模块驱动,依赖于@Import实现。

@Import作用是装载导入类,主要包括@Configuration class,ImportSelector实现类,ImportBeanDefinitionRegistrar实现类。

XML时代,经常是@Import,<context:component-scan>,<context:annotation-config>一起使用。

<context:annotation-config>(注解配置)中大概率有我们需要找的逻辑。

根据 Spring Framework 2.0引入的可扩展的XML编程机制,XML Schema命名空间需要与Handler建立映射关系。

该关系配置在相对于classpath下的/META-INF/spring.handlers中。

查看ContextNamespaceHandler 源码

public class ContextNamespaceHandler extends NamespaceHandlerSupport {
@Override
public void init() {
//省略其他代码
registerBeanDefinitionParser("annotation-config",
new AnnotationConfigBeanDefinitionParser());
}
}复制代码

对应AnnotationConfigBeanDefinitionParser这个就是要找的入口

找核心类

从AnnotationConfigBeanDefinitionParser的parse方法开始一路向下,找到

AnnotationConfigUtils.registerAnnotationConfigProcessors中注册了ConfigurationClassPostProcessor。

img

ConfigurationClassPostProcessor类注释说明

\1. 用于的引导处理@Configuration类

\2. context:annotation-config/或 context:component-scan/时会注册

否则需要手工编程

\3. ConfigurationClassPostProcessor第一优先级,保证

@Configuration}类中声明@Bean,在其他 BeanFactoryPostProcessor执行之前被注册

扩展

AnnotationConfigApplicationContext中new AnnotationBeanDefinitionReader也调用了 AnnotationConfigUtils .

registerAnnotationConfigProcessors

从类注释中,可以看出ConfigurationClassPostProcessor就是要找的核心类

找核心方法

查看 ConfigurationClassPostProcessor 的层级关系为

img

Aware系列注入相应资源,Ordered设置优先级,值得关注的就是

postProcessBeanDefinitionRegistry了。

postProcessBeanDefinitionRegistry其内部有2个方法

  1. postProcessBeanDefinitionRegistry在BeanDefinition注册之后,BeanFactoryPostProcessor执行之前,修改或重写BeanDefinition
  2. 继承自BeanFactoryPostProcessor的postProcessBeanFactory,BeanDefinition加载之后,Bean实例化之前,重写或添加BeanDefinition,修改BeanFactory

浏览2个方法,都有processConfigBeanDefinitions,从名称可以看出是处理配置类Bean定义

img

ConfigurationClassPostProcessor#processConfigBeanDefinitions就是要找的核心方法

梳理流程

public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
String[] candidateNames = registry.getBeanDefinitionNames();

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);
}
}
else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
}
}

// 没有找到 @Configuration classes 立即返回
if (configCandidates.isEmpty()) {
return;
}
//根据@Order 值进行排序
configCandidates.sort((bd1, bd2) -> {
int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());
int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());
return Integer.compare(i1, i2);
});
//通过封闭的应用程序上下文, 检测任何自定义bean名称生成策略
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();
}
// 解析@Configuration class
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 {
parser.parse(candidates);
parser.validate();

Set<ConfigurationClass> configClasses = new LinkedHashSet<>(parser.getConfigurationClasses());
configClasses.removeAll(alreadyParsed);
// 读ConfigurationClass的信息,创建BeanDefinition
if (this.reader == null) {
this.reader = new ConfigurationClassBeanDefinitionReader(
registry, this.sourceExtractor, this.resourceLoader, this.environment,
this.importBeanNameGenerator, parser.getImportRegistry());
}
this.reader.loadBeanDefinitions(configClasses);
alreadyParsed.addAll(configClasses);

candidates.clear();
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);
if (ConfigurationClassUtils.checkConfigurationClassCandidate(bd, this.metadataReaderFactory) &&
!alreadyParsedClasses.contains(bd.getBeanClassName())) {
candidates.add(new BeanDefinitionHolder(bd, candidateName));
}
}
}
candidateNames = newCandidateNames;
}
}
while (!candidates.isEmpty());

// 将ImportRegistry注册为bean以支持importware@Configuration类
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();
}
}复制代码

ConfigurationClassPostProcessor#processConfigBeanDefinitions核心如下:

  1. 根据@Order 值进行排序
  2. 解析@Configuration class 为ConfigurationClass对象
  3. 读ConfigurationClass的信息,创建BeanDefinition
  4. 将ImportRegistry注册为bean以支持importware@Configuration类

重点关注解析方法

ConfigurationClassParser#parse方法负责解析@Configuration class 为ConfigurationClass对象

查阅其源码如下:

ConfigurationClassParser#doProcessConfigurationClass代码如下:

protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
throws IOException {

if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
// Recursively process any member (nested) classes first
processMemberClasses(configClass, sourceClass);
}

// Process any @PropertySource annotations
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");
}
}

// Process any @ComponentScan annotations
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
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
for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
if (bdCand == null) {
bdCand = holder.getBeanDefinition();
}
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;
}复制代码

ConfigurationClassParser#doProcessConfigurationClass(ConfigurationClass,AnnatationMetatdata)将@PropertySource@ComponentScan@Import,@ImportResource,@Bean等一起处理了。

看到这里基本逻辑已经理清 了,但是有一个疑问

@Configuration中的@Bean没有其他特殊处理吗?

浏览代码解决疑问

从上边浏览的代码可以看到完全模式,会被AOP增强

那什么是完全模式呢?在ConfigurationClassUtils找到如下方法:

public class ConfigurationClassUtils{
//省略其他方法
public static boolean isFullConfigurationCandidate(AnnotationMetadata metadata) {
return metadata.isAnnotated(Configuration.class.getName());
}
}复制代码

@Configuration class是完全模式,@Component,@Bean是轻量级模式

那AOP增强了作用是什么呢?查看 ConfigurationClassEnhancer 的类注释如下:

/**

* Enhances {@link

Configuration

} classes by generating a CGLIB subclass which

* interacts with the Spring container to respect bean scoping semantics for

* {@code @Bean} methods. Each such {@code @Bean} method will be overridden in

* the generated subclass, only delegating to the actual {@code @Bean} method

* implementation if the container actually requests the construction of a new

* instance. Otherwise, a call to such an {@code @Bean} method serves as a

* reference back to the container, obtaining the corresponding bean by name.

-

* @author Chris Beams

* @author Juergen Hoeller

* @since 3.0

* @see #enhance

* @see

ConfigurationClassPostProcessor

*/

class ConfigurationClassEnhancer {

大概意思如下:

通过CGLIB增强@Configuration class。

每个@Bean方法会生成子类。

首次被调用时,@Bean方法会被执行用于创建bean实例;

再次被调用时,不会再执行创建bean实例,而是根据bean名称返回首次该方法被执行时创建的bean实例。

总结

1.ConfigurationClassPostProcessor负责筛选@Component Class、@Configuration Class以及@Bean定义的Bean,**

2.ConfigurationClassParser从候选的Bean定义中解析出ConfigurationClass集合,随后被3.ConfigurationClassBeanDefinitionReader转换为BeanDefinition

4.ConfigurationClassParser的解析顺序,

@PropertySource->@ComponentScan->@Import->@ImportResource->@Bean->接口的默认方法->处理父类

5.@Configuration class是完全模式,@Component,@Bean是轻量级模式

6.CGLIB增强@Configuration class。每个@Bean方法会生成子类。

首次被调用时,@Bean方法会被执行用于创建bean实例;

再次被调用时,不会再执行创建bean实例,而是根据bean名称返回首次该方法被执行时创建的bean实例。

文章目录
  1. 1. @Enable驱动逻辑
    1. 1.1. 找入口
    2. 1.2. 找核心类
    3. 1.3. 梳理流程
    4. 1.4. 重点关注解析方法
    5. 1.5. 浏览代码解决疑问
  2. 2. 总结