@Configuration 類型的 class 需要知道的細節(jié)
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@Configuration.class文件如何被spring加載的？
@Configuration.class文件如何被轉化為BeanDefinition放入spring容器的？
@Configuration的BeanDefinition如何轉化為ConfigurationClass對象的
ConfigurationClass對象屬性在哪里開始被解析的？
@Configuration的BeanDefinition的beanClass值何時變成proxy代理類的，為什么要變
@Configuration類最終會生成cglib proxy代理類，這個由@Configuration類生成的cglib proxy代理類如何實例化的
我們能從中得到的擴展點有哪些
@Configuration注解作用
@Configuration標識的類有這些特性：可以聲明多個@Bean方法，且在運行時被spring容器處理來生成BeanDefinition。@Configuration類是被AnnotationConfigWebApplicationContext啟動(bootstrap)處理流程的。聲明方式如下代碼
@Configuration
?public?class?AppConfig?{
????@Bean
????public?MyBean?myBean()?{
????????//?instantiate,?configure?and?return?bean?...
????}
}
@Configuration class存在如下約束，如下圖
@Configuration class源碼加載分析
@Configuration相關的類
如果IDE你使用的Idea，double Shift鍵，輸入ConfigurationClass，會出現一長列的類，
這些類分工協作，從加載標識@Configuration的.class文件，到生成BeanDefinition，再到生成ConfigurationClass對象，再到解析ConfigurationClass對象，即解析@ConfigurationClass class類中@Bean、@Import、@ImportResource等注解
ConfigurationClass：?專門表示@Configuration class。存儲解析@Configuration class的信息
ConfigurationClassPostProcessor：?專門用于處理@Configuration class的BeanDefinitoinRegistryPostProcessor（BeanFactoryPostProcessor子類)
AnnotationConfigUtils?：專門注冊BeanPostProcessor和BeanFactoryPostProcessor到spring容器
@Configuration解析過程
ConfigurationClassPostProcessor實例創(chuàng)建過程
我們剛說過，ConfigurationClassPostProcessor是處理@Configuration class的核心組件，它是BeanFactoryPostProcessor類型子類且是BeanDefinitoinRegistryPostProcessor類型子類。BeanFactoryPostProcessor是AbstractApplicationContext's post-processor handling技術的規(guī)范接口，在項目啟動較早時段，它便開始工作?；蛘哒f任何spring boot項目啟動時都是走post-processor handling處理邏輯，這個邏輯的入口在PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors()方法，代碼如下
PostProcessorRegistrationDelegate?class
public?static?void?invokeBeanFactoryPostProcessors(
????????ConfigurableListableBeanFactory?beanFactory,?List<BeanFactoryPostProcessor>?beanFactoryPostProcessors)?{
????···
????//?Invoke?BeanDefinitionRegistryPostProcessors?first,?if?any.
????if?(beanFactory?instanceof?BeanDefinitionRegistry)?{
????????BeanDefinitionRegistry?registry?=?(BeanDefinitionRegistry)?beanFactory;
????????List?currentRegistryProcessors?=?new?ArrayList<>();
????????//?First,?invoke?the?BeanDefinitionRegistryPostProcessors?that?implement?PriorityOrdered.
????????String[]?postProcessorNames?=
????????????????beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class,?true,?false);?//?(1)
????????for?(String?ppName?:?postProcessorNames)?{
????????????if?(beanFactory.isTypeMatch(ppName,?PriorityOrdered.class))?{
????????????????currentRegistryProcessors.add(beanFactory.getBean(ppName,?BeanDefinitionRegistryPostProcessor.class));?//?(2)
????????????}
????????}
????????sortPostProcessors(currentRegistryProcessors,?beanFactory);
????????//?將@Configuration類生成BeanDefinition，此時的BeanDefinition.beanClass為原類class對象
????????invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors,?registry);?//?(3)
????????//?Now,?invoke?the?postProcessBeanFactory?callback?of?all?processors?handled?so?far.
????????//?將(3)處的BeanDefinition.beanClass賦值為proxy代理類
????????nvokeBeanFactoryPostProcessors(registryProcessors,?beanFactory);(4)
????}
????···
}
這個方法處理所有的BeanFactoryPostProcessor類型對象，但是通過優(yōu)先級來規(guī)定先后處理順序，優(yōu)先級維度有兩個:1:BeanDefinitionRegistryPostProcessor類型和BeanFactoryPostProcessor類型；2:PriorityOrdered和Ordered。而
ConfigurationClassPostProcessor同時實現了BeanDefinitionRegistryPostProcessor和PriorityOrdered，所以它得到最優(yōu)先處理的機會
如上方法(1)處，從spring容器獲取BeanDefinitionRegistryPostProcessor類型的beanName, 這個時期只有ConfigurationClassPostProcessor的beanName滿足，需要指出：ConfigurationClassPostProcessor是通過硬編碼的方式注冊到spring容器的，詳見AnnotationConfigUtils類)，接著執(zhí)行如上方法(2)處，以beanName為key從spring容器中獲取ConfigurationClassPostProcessor實例。
應用ConfigurationClassPostProcessor實例加載@Configuration進行BeanDefinition注冊
如上方法(3)處，即為應用ConfigurationClassPostProcessor實例。
PostProcessorRegistrationDelegate?class
private?static?void?invokeBeanDefinitionRegistryPostProcessors(
????????Collection?postProcessors,?BeanDefinitionRegistry?registry)?{
????for?(BeanDefinitionRegistryPostProcessor?postProcessor?:?postProcessors)?{
????????postProcessor.postProcessBeanDefinitionRegistry(registry);
????}
}
ConfigurationClassPostProcessor?class
@Override
public?void?postProcessBeanDefinitionRegistry(BeanDefinitionRegistry?registry)?{
????processConfigBeanDefinitions(registry);
}
從方法名大概就知道方法的作用了，會調用所有BeanDefinitionRegistryPostProcessor類型的postProcessBeanDefinitionRegistry()方法，此處只有ConfigurationClassPostProcessor符合。
應用ConfigurationClassPostProcessor實例將BeanDefinition.beanClass生成proxy代理類
如上invokeBeanFactoryPostProcessors方法(4)處，經過了方法(3)的處理，@Configuration類已經生成BeanDefinition，此時BeanDefinition.beanClass值為原類class對象。而方法(4)處目的是將BeanDefinition.beanClass賦值為proxy代理類，這里留個問題，其他為什么要設置成proxy代理類呢
關于方法(3)和方法(4)要做的事，參考下圖，時機和作用清晰的對比和展示
@Configuration class過程解析
下面的方法就是解析@Configuration class的核心邏輯了。解析過程可以總結分三步，正好對應著方法中(1),(2),(3)處
ConfigurationClassPostProcessor?class
public?void?processConfigBeanDefinitions(BeanDefinitionRegistry?registry)?{
????List?configCandidates?=?new?ArrayList<>();
????String[]?candidateNames?=?registry.getBeanDefinitionNames();?
????for?(String?beanName?:?candidateNames)?{
????????BeanDefinition?beanDef?=?registry.getBeanDefinition(beanName);
????????if?(ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef,?this.metadataReaderFactory)){
????????????configCandidates.add(new?BeanDefinitionHolder(beanDef,?beanName));//(1)
????????}
????}
????···?排序等
s
????//?Parse?each?@Configuration?class
????ConfigurationClassParser?parser?=?new?ConfigurationClassParser(
????????????this.metadataReaderFactory,?this.problemReporter,?this.environment,
????????????this.resourceLoader,?this.componentScanBeanNameGenerator,?registry);
????Set?candidates?=?new?LinkedHashSet<>(configCandidates);
????Set?alreadyParsed?=?new?HashSet<>(configCandidates.size());
????do?{
????????parser.parse(candidates);?//(2)
????????parser.validate();
????????Set?configClasses?=?new?LinkedHashSet<>(parser.getConfigurationClasses());
????????//?Read?the?model?and?create?bean?definitions?based?on?its?content
????????this.reader?=?new?ConfigurationClassBeanDefinitionReader(
????????????????registry,?this.sourceExtractor,?this.resourceLoader,?this.environment,
????????????????this.importBeanNameGenerator,?parser.getImportRegistry());
????????this.reader.loadBeanDefinitions(configClasses);?//(3)
????}
????while?(!candidates.isEmpty());
????···?···
}
step1: 獲取候選者
從spring容器拿到所有的beanDefinitionNames，然后遍歷驗證獲得候選者，驗證的依據是class metadata是否含有@Configuration注解，從下面我們可知，此時，beanDefinitionNames中只有consumerFeignApp符合條件。所以候選者就是consumerFeignApp及他的beanDefinition
step2: 通過候選者獲取ConfigurationClass
找到了候選者，下面就對候選者進行解析，解析的全部功能和邏輯都集中在ConfigurationClassParser類中，看名稱可知，這個類專業(yè)解析@Configuration類。
ConfigurationClassParser?class
public?void?parse(Set?configCandidates) ?{
????for?(BeanDefinitionHolder?holder?:?configCandidates)?{
????????BeanDefinition?bd?=?holder.getBeanDefinition();
????????if?(bd?instanceof?AnnotatedBeanDefinition)?{
????????????parse(((AnnotatedBeanDefinition)?bd).getMetadata(),?holder.getBeanName());
????????}
????????...
????}
????this.deferredImportSelectorHandler.process();
}
protected?final?void?parse(AnnotationMetadata?metadata,?String?beanName)?throws?IOException?{
????processConfigurationClass(new?ConfigurationClass(metadata,?beanName));
}
protected?void?processConfigurationClass(ConfigurationClass?configClass)?throws?IOException?{
????//?評估標識@Configuration的類是否滿足條件去加載，這是條件注解@ConditionalXXX起的作用
????//?實際開發(fā)中，我們可以依據這個功能實現靈活的加載配置(如讓誰加載進來，不讓誰加載進來^_^)
????if?(this.conditionEvaluator.shouldSkip(configClass.getMetadata(),?ConfigurationPhase.PARSE_CONFIGURATION))?{
????????return;
????}
????//?Recursively?process?the?configuration?class?and?its?superclass?hierarchy.
????SourceClass?sourceClass?=?asSourceClass(configClass);
????do?{
????????sourceClass?=?doProcessConfigurationClass(configClass,?sourceClass);
????}
????while?(sourceClass?!=?null);
????//?所有加載的@Configuration類都會轉為ConfigurationClass放入這個map中
????this.configurationClasses.put(configClass,?configClass);
}
protected?final?SourceClass?doProcessConfigurationClass(ConfigurationClass?configClass,?SourceClass?sourceClass){
????//?為了集中說明意圖，隱藏了代碼
????//?Recursively?process?any?member?(nested)?classes?first
????//?Process?any?@PropertySource?annotations
????//?Process?any?@ComponentScan?annotations
????for?(AnnotationAttributes?componentScan?:?componentScans)?{
????????for?(BeanDefinitionHolder?holder?:?scannedBeanDefinitions)?{
????????????if?()?{
????????????????//?進入遞歸調用
????????????????parse(bdCand.getBeanClassName(),?holder.getBeanName());
????????????}
????????}
????}
????//?Process?any?@Import?annotations
????//?Process?any?@ImportResource?annotations
????//?Process?individual?@Bean?methods
????//?Process?default?methods?on?interfaces
????//?Process?superclass,?if?any
????//?No?superclass?->?processing?is?complete
????return?null;
}
如上方法整體的邏輯為對ConfigurationClass和SourceClass解析，檢查他們有沒有@ComponentScan，@Import，@Bean methods，@ImportResource，@PropertySource這些注解，如果有，分別對其解析，解析后的結果放入ConfigurationClass的各屬性中
各個注解的屬性值中可能又包含@Configuration注解，又要對包含的@Configuration注解進行解析，這樣形成了遞歸，所以解析過程中有三個方法形成了三角遞歸調用的邏輯，
這一步會將我們項目中定義的@Configuration類都加載進來，你可能有疑問，難道項目中我們自己定義的@Configuration類都是靠遞歸加載進來的？答案當然是NO，請注意@ComponentScan注解，這個注解的解析器很厲害，它把所有的標識@Component注解的class加載進來，而@Configuration，@RestController，@Service，@Repository等都包含@Component，所有這些注解的class都會加載進來形成BeanDefinition存入spring 容器(解析過程詳見ComponentScanAnnotationParser)。說回來，對于@ComponentScan解析器加載進來的BeanDefinitoin，會進行時@Configuration進行過濾，從而得到@Configuration類，再次調用parse()方法，這時體現出三角遞歸調用了。此時，項目中所有我們自定義的@Configuration類都獲取到了
step3: 解析每個ConfigurationClass
step2中對@Configuration類的@Import，@Bean methods，@ImportResource進行解析，解析的結果放入ConfigurationClass對象的importBeanDefinitionRegistrars，beanMethods，importedResources，metadata等屬性。
所以，step2將@Configuration類的解析結果都放入了ConfigurationClass對象，即ConfigurationClass對象包裝了@Configuration類的所有信息。
回到ConfigurationClassPostProcessor.processConfigBeanDefinitions()方法(3)處，現在，我們解析ConfigurationClass，而解析ConfigurationClass過程由ConfigurationClassBeanDefinitionReader類負責的
看code
ConfigurationClassBeanDefinitionReader?class
public?void?loadBeanDefinitions(Set?configurationModel)?{
????TrackedConditionEvaluator?trackedConditionEvaluator?=?new?TrackedConditionEvaluator();
????for?(ConfigurationClass?configClass?:?configurationModel)?{
????????loadBeanDefinitionsForConfigurationClass(configClass,?trackedConditionEvaluator);
????}
}
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;
????}
????if?(configClass.isImported())?{
????????registerBeanDefinitionForImportedConfigurationClass(configClass);
????}
????for?(BeanMethod?beanMethod?:?configClass.getBeanMethods())?{
????????loadBeanDefinitionsForBeanMethod(beanMethod);
????}
????loadBeanDefinitionsFromImportedResources(configClass.getImportedResources());
????loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars());
}
看loadBeanDefinitionsForConfigurationClass()方法，方法主要功能為對ConfigurationClass的beanMethods，importedResources，importBeanDefinitionReistrars屬性進行解析，為什么要對這三個屬性進行解析呢，看看這三個其@Import，@Bean methods，@ImportResource的用法
@Import(DispatcherServletConfiguration.class)
@ImportResource("classpath:/com/acme/database-config.xml")
protected?static?class?DispatcherServletRegistrationConfiguration?{
????@Bean(name?=?DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
????public?DispatcherServletRegistrationBean?dispatcherServletRegistration(){
????????...
????}
}
可以看到，這三個注解的屬性值都是類或者配置文件或者加載文件的類，所以，需要解析，從而將解析到的.class文件轉化為BeanDefinition放入spring容器。
@Configuration類的cglib代理類實例化分析
由于@Configuration注解的都是類，而非接口，所有這里使用的是cglib代理技術，ConfigurationClassEnhancer包裝了cglib。這里我們實際工作中可以直接復用ConfigurationClassEnhancer滿足我們生成代理類的場景
實現自BeanFactoryPostProcessor.postProcessBeanFactory
ConfigurationClassPostProcessor?class
@Override
public?void?postProcessBeanFactory(ConfigurableListableBeanFactory?beanFactory)?{
????//?生成代理
????enhanceConfigurationClasses(beanFactory);
????beanFactory.addBeanPostProcessor(new?ImportAwareBeanPostProcessor(beanFactory));
}
ConfigurationClassPostProcessor.ConfigurationClassEnhancer?class
public?void?enhanceConfigurationClasses(ConfigurableListableBeanFactory?beanFactory)?{
????Map?configBeanDefs?=?new?LinkedHashMap<>();
????for?(String?beanName?:?beanFactory.getBeanDefinitionNames())?{
????????BeanDefinition?beanDef?=?beanFactory.getBeanDefinition(beanName);
????????if?(ConfigurationClassUtils.isFullConfigurationClass(beanDef))?{
????????????if?(!(beanDef?instanceof?AbstractBeanDefinition))?{
????????????????throw?
????????????}
????????????configBeanDefs.put(beanName,?(AbstractBeanDefinition)?beanDef);
????????}
????}
????ConfigurationClassEnhancer?enhancer?=?new?ConfigurationClassEnhancer();
????for?(Map.Entry?entry?:?configBeanDefs.entrySet())?{
????????AbstractBeanDefinition?beanDef?=?entry.getValue();
????????//?If?a?@Configuration?class?gets?proxied,?always?proxy?the?target?class
????????beanDef.setAttribute(AutoProxyUtils.PRESERVE_TARGET_CLASS_ATTRIBUTE,?Boolean.TRUE);
????????//?Set?enhanced?subclass?of?the?user-specified?bean?class
????????Class?configClass?=?beanDef.resolveBeanClass(this.beanClassLoader);
????????if?(configClass?!=?null)?{
????????????Class?enhancedClass?=?enhancer.enhance(configClass,?this.beanClassLoader);
????????????if?(configClass?!=?enhancedClass)?{
????????????????beanDef.setBeanClass(enhancedClass);
????????????}
????????}
????}
}
ConfigurationClassPostProcessor.ConfigurationClassEnhancer?class
public?Class?enhance(Class?configClass,?@Nullable?ClassLoader?classLoader)?{
????if?(EnhancedConfiguration.class.isAssignableFrom(configClass))?{
????????return?configClass;
????}
????Class?enhancedClass?=?createClass(newEnhancer(configClass,?classLoader));
????return?enhancedClass;
}
代理的代碼很清晰，很值得我們學習
it`s time to summary
整個過程可以看做是一顆小樹長成參天大樹，consumerFeignApp就是樹苗，而我們項目的代碼就是后來大樹的枝干和葉子。枝干和葉子與@ComponentScan，@Import，@Bean methods，@ImportResource，@PropertySource，@Configuration交織在一起被解析出來，生成beanDefinition、實例對象或代理類。
本文主要說明了標識了@Configuration的.class文件，是如何被解析成ConfigurationClass，再到轉化為ConfigurationClassBeanDefinition放入spring容器，再到如何解析ConfigurationClass對象屬性。為了集中闡述@Configuration，所以，其他的部分這里不做詳述和延展。如果閱讀后你有所收獲，共享歡喜
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1，2，3，4相信你已經有答案了，現在，我們看看擴展點有什么
加載一些package目錄下的.class文件
ClassPathBeanDefinitionScanner?scanner?=?new?ClassPathBeanDefinitionScanner(this.registry,
????????????componentScan.getBoolean("useDefaultFilters"),?this.environment,?this.resourceLoader);
Set?beanDefinitions?=?scanner.doScan(StringUtils.toStringArray(basePackages));
如此兩行代碼就實現了加載package目錄下的.class文件的功能。詳見ComponentScanAnnotationParser.parse()方法 source:?//yaoyuanyy.github.io/2019/12/12/springboot%20@Configuration類型的class需要知道的細節(jié)
喜歡，在看