SpringBoot之自动装配
1、自动装配过程
启动类注解一览
@SpringBootApplication @EnableDiscoveryClient @MapperScan("com.tpl.system.dao") public class SystemApplication { public static void main(String[] args) { SpringApplication.run(SystemApplication.class, args); } }
查看@SpringBootApplication注解
@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @SpringBootConfiguration @EnableAutoConfiguration @ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class), @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) }) public @interface SpringBootApplication { /** * Exclude specific auto-configuration classes such that they will never be applied. * @return the classes to exclude */ @AliasFor(annotation = EnableAutoConfiguration.class) Class<?>[] exclude() default {}; /** * Exclude specific auto-configuration class names such that they will never be * applied. * @return the class names to exclude * @since 1.3.0 */ @AliasFor(annotation = EnableAutoConfiguration.class) String[] excludeName() default {}; ... }
一旦加上@EnableAutoConfiguration就开启了自动装配，代码如下：
@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @AutoConfigurationPackage @Import(AutoConfigurationImportSelector.class) public @interface EnableAutoConfiguration { String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration"; /** * Exclude specific auto-configuration classes such that they will never be applied. * @return the classes to exclude */ Class<?>[] exclude() default {}; /** * Exclude specific auto-configuration class names such that they will never be * applied. * @return the class names to exclude * @since 1.3.0 */ String[] excludeName() default {}; }
继续看AutoConfigurationImportSelector.class，实现了DeferredImportSelector
public class AutoConfigurationImportSelector implements DeferredImportSelector, BeanClassLoaderAware, ResourceLoaderAware, BeanFactoryAware, EnvironmentAware, Ordered { ... 省略部分代码 @Override public String[] selectImports(AnnotationMetadata annotationMetadata) {
1、判断自动装配开关是否打开，观察spring.boot.enableautoconfiguration是否为true if (!isEnabled(annotationMetadata)) { return NO_IMPORTS; }
2、收集需要自动装配的类 AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(annotationMetadata); return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations()); } ... }
getAutoConfigurationEntry(annotationMetadata),收集需要自动装配的类
/** * Return the {@link AutoConfigurationEntry} based on the {@link AnnotationMetadata} * of the importing {@link Configuration @Configuration} class. * @param annotationMetadata the annotation metadata of the configuration class * @return the auto-configurations that should be imported */ protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {
//1、检查自动装配开关 if (!isEnabled(annotationMetadata)) { return EMPTY_ENTRY; }
//2、获取EnableAutoConfiguration中的参数，exclude()/excludeName() AnnotationAttributes attributes = getAttributes(annotationMetadata);
//3、获取需要自动装配的所有配置类，读取META-INF/spring.factories List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
//4、去重,List转Set再转List configurations = removeDuplicates(configurations);
//5、从EnableAutoConfiguration的exclude/excludeName属性中获取排除项 Set<String> exclusions = getExclusions(annotationMetadata, attributes);
//6、查看排除项是否在configurations中，不在报错 checkExcludedClasses(configurations, exclusions);
//7、从configurations去除exclusions configurations.removeAll(exclusions);
//8、对configurations进行过滤，ex剔除掉@Conditional条件不成立的配置类 configurations = getConfigurationClassFilter().filter(configurations);
//9、把AutoConfigurationImportEvent绑定在所有AutoConfigurationImportListener子类实例上 fireAutoConfigurationImportEvents(configurations, exclusions);
//10、返回(configurations, exclusions)组 return new AutoConfigurationEntry(configurations, exclusions); }
上面代码主要实现三个功能：
1、获取META-INF/spring.factories中EnableAutoConfiguration所对应的Configuration列表
2、根据注解中的exclude和exludeName进行筛选
3、再把不满足@Conditional的配置类也筛选掉
2、何时进行自动装配
前面的环节只是确认了哪些类需要被装配，当AbstractApplicationContext执行refresh方法里的invokeBeanFactoryPostProcessors(beanFactory)方法时会执行自动装配。
// Invoke factory processors registered as beans in the context. invokeBeanFactoryPostProcessors(beanFactory);
探索
/** * Instantiate and invoke all registered BeanFactoryPostProcessor beans, * respecting explicit order if given. * <p>Must be called before singleton instantiation. */ protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) { PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors()); // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor) if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) { beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory)); beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader())); } }
继续
public static void invokeBeanFactoryPostProcessors( ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) { // Invoke BeanDefinitionRegistryPostProcessors first, if any. Set<String> processedBeans = new HashSet<>(); if (beanFactory instanceof BeanDefinitionRegistry) { BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory; List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>(); List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>(); for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) { if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) { BeanDefinitionRegistryPostProcessor registryProcessor = (BeanDefinitionRegistryPostProcessor) postProcessor; registryProcessor.postProcessBeanDefinitionRegistry(registry); registryProcessors.add(registryProcessor); } else { regularPostProcessors.add(postProcessor); } } ... }
观察BeanDefinitionRegistryPostProcessor
/** * Extension to the standard {@link BeanFactoryPostProcessor} SPI, allowing for * the registration of further bean definitions <i>before</i> regular * BeanFactoryPostProcessor detection kicks in. In particular, * BeanDefinitionRegistryPostProcessor may register further bean definitions * which in turn define BeanFactoryPostProcessor instances. * * @author Juergen Hoeller * @since 3.0.1 * @see org.springframework.context.annotation.ConfigurationClassPostProcessor */ public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor { /** * Modify the application context's internal bean definition registry after its * standard initialization. All regular bean definitions will have been loaded, * but no beans will have been instantiated yet. This allows for adding further * bean definitions before the next post-processing phase kicks in. * @param registry the bean definition registry used by the application context * @throws org.springframework.beans.BeansException in case of errors */ void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException; }
我们看ConfigurationClassPostProcessor这个类
public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPostProcessor, PriorityOrdered, ResourceLoaderAware, BeanClassLoaderAware, EnvironmentAware { ...省略部分代码 /** * Prepare the Configuration classes for servicing bean requests at runtime * by replacing them with CGLIB-enhanced subclasses. */ @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) { int factoryId = System.identityHashCode(beanFactory); if (this.factoriesPostProcessed.contains(factoryId)) { throw new IllegalStateException( "postProcessBeanFactory already called on this post-processor against " + beanFactory); } this.factoriesPostProcessed.add(factoryId); if (!this.registriesPostProcessed.contains(factoryId)) { // BeanDefinitionRegistryPostProcessor hook apparently not supported... // Simply call processConfigurationClasses lazily at this point then. processConfigBeanDefinitions((BeanDefinitionRegistry) beanFactory); } enhanceConfigurationClasses(beanFactory); beanFactory.addBeanPostProcessor(new ImportAwareBeanPostProcessor(beanFactory)); } /** * Build and validate a configuration model based on the registry of * {@link Configuration} classes. */ public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) { List<BeanDefinitionHolder> configCandidates = new ArrayList<>(); String[] candidateNames = registry.getBeanDefinitionNames(); for (String beanName : candidateNames) { BeanDefinition beanDef = registry.getBeanDefinition(beanName); if (beanDef.getAttribute(ConfigurationClassUtils.CONFIGURATION_CLASS_ATTRIBUTE) != null) { 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)); } } // Return immediately if no @Configuration classes were found if (configCandidates.isEmpty()) { return; } // Sort by previously determined @Order value, if applicable 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( AnnotationConfigUtils.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 解析每一个注解类 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 { parser.parse(candidates); parser.validate(); 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()); } 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()); // 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(); } }
通过ConfigurationClassParser解析注解类
public void parse(Set<BeanDefinitionHolder> configCandidates) { for (BeanDefinitionHolder holder : configCandidates) { BeanDefinition bd = holder.getBeanDefinition(); try { if (bd instanceof AnnotatedBeanDefinition) { parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName()); } else if (bd instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) bd).hasBeanClass()) { parse(((AbstractBeanDefinition) bd).getBeanClass(), holder.getBeanName()); } else { parse(bd.getBeanClassName(), holder.getBeanName()); } } catch (BeanDefinitionStoreException ex) { throw ex; } catch (Throwable ex) { throw new BeanDefinitionStoreException( "Failed to parse configuration class [" + bd.getBeanClassName() + "]", ex); } } this.deferredImportSelectorHandler.process(); }
在这里大家留意一下最后一句this.deferredImportSelectorHandler.process()方法，在这里将会对DeferredImportSelector进行处理，这样我们就和AutoConfigurationSelectImporter结合到一起了。
3、总结
- 最初的入口时@SpringBootApplication 然后是@EnableAutoConfiguration，其中存在exclude和excludeName可以排除指定的Configuration
- @Import(AutoConfigurationImportSelector.class)，AutoConfigurationImportSelector实现了DeferredImportSelector（DeferredImportSelector是延期导入，当所有的@Configuration都处理过后才会执行）
-
获取META-INF/spring.factories中EnableAutoConfiguration所对应的Configuration列表，然后根据exclude/excludeName以及Condition条件过滤获取最终需要自动装配的类
- 处理@Configuration的核心还是ConfigurationClassPostProcessor，这个类实现了BeanFactoryPostProcessor，因此在AbstractApplicationContext的refresh方法中
执行invokeBeanFactoryPostProcessors时会进行自动装配。
