SpringBoot自动配置原理是什么？
面试过程中问得最多的可能是自动装配的原理，而自动装配是在启动过程中完成，只不过在刚开始的时候我们选择性的跳过了，下面详细讲解自动装配的过程。
推荐学习：谈起SpringBoot，面试官（Java）必问题：讲述一下 SpringBoot 自动装配原理？
1、在springboot的启动过程中，有一个步骤是创建上下文，如果不记得可以看下面的代码：
public ConfigurableApplicationContext run(String... args) { StopWatch stopWatch = new StopWatch(); stopWatch.start(); ConfigurableApplicationContext context = null; Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>(); configureHeadlessProperty(); SpringApplicationRunListeners listeners = getRunListeners(args); listeners.starting(); try { ApplicationArguments applicationArguments = new DefaultApplicationArguments(args); ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments); configureIgnoreBeanInfo(environment); Banner printedBanner = printBanner(environment); context = createApplicationContext(); exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[] { ConfigurableApplicationContext.class }, context); //此处完成自动装配的过程 prepareContext(context, environment, listeners, applicationArguments, printedBanner); refreshContext(context); afterRefresh(context, applicationArguments); stopWatch.stop(); if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch); } listeners.started(context); callRunners(context, applicationArguments); } catch (Throwable ex) { handleRunFailure(context, ex, exceptionReporters, listeners); throw new IllegalStateException(ex); } try { listeners.running(context); } catch (Throwable ex) { handleRunFailure(context, ex, exceptionReporters, null); throw new IllegalStateException(ex); } return context; }
2、在prepareContext方法中查找load方法，一层一层向内点击，找到最终的load方法
//prepareContext方法 private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment, SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) { context.setEnvironment(environment); postProcessApplicationContext(context); applyInitializers(context); listeners.contextPrepared(context); if (this.logStartupInfo) { logStartupInfo(context.getParent() == null); logStartupProfileInfo(context); } // Add boot specific singleton beans ConfigurableListableBeanFactory beanFactory = context.getBeanFactory(); beanFactory.registerSingleton("springApplicationArguments", applicationArguments); if (printedBanner != null) { beanFactory.registerSingleton("springBootBanner", printedBanner); } if (beanFactory instanceof DefaultListableBeanFactory) { ((DefaultListableBeanFactory) beanFactory) .setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding); } if (this.lazyInitialization) { context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor()); } // Load the sources Set<Object> sources = getAllSources(); Assert.notEmpty(sources, "Sources must not be empty"); //load方法完成该功能 load(context, sources.toArray(new Object[0])); listeners.contextLoaded(context); } /** * Load beans into the application context. * @param context the context to load beans into * @param sources the sources to load * 加载bean对象到context中 */ protected void load(ApplicationContext context, Object[] sources) { if (logger.isDebugEnabled()) { logger.debug("Loading source " + StringUtils.arrayToCommaDelimitedString(sources)); } //获取bean对象定义的加载器 BeanDefinitionLoader loader = createBeanDefinitionLoader(getBeanDefinitionRegistry(context), sources); if (this.beanNameGenerator != null) { loader.setBeanNameGenerator(this.beanNameGenerator); } if (this.resourceLoader != null) { loader.setResourceLoader(this.resourceLoader); } if (this.environment != null) { loader.setEnvironment(this.environment); } loader.load(); } /** * Load the sources into the reader. * @return the number of loaded beans */ int load() { int count = 0; for (Object source : this.sources) { count += load(source); } return count; }
3、实际执行load的是BeanDefinitionLoader中的load方法，如下：
//实际记载bean的方法 private int load(Object source) { Assert.notNull(source, "Source must not be null"); //如果是class类型，启用注解类型 if (source instanceof Class<?>) { return load((Class<?>) source); } //如果是resource类型，启动xml解析 if (source instanceof Resource) { return load((Resource) source); } //如果是package类型，启用扫描包，例如@ComponentScan if (source instanceof Package) { return load((Package) source); } //如果是字符串类型，直接加载 if (source instanceof CharSequence) { return load((CharSequence) source); } throw new IllegalArgumentException("Invalid source type " + source.getClass()); }
4、下面方法将用来判断是否资源的类型，是使用groovy加载还是使用注解的方式
private int load(Class<?> source) { //判断使用groovy脚本 if (isGroovyPresent() && GroovyBeanDefinitionSource.class.isAssignableFrom(source)) { // Any GroovyLoaders added in beans{} DSL can contribute beans here GroovyBeanDefinitionSource loader = BeanUtils.instantiateClass(source, GroovyBeanDefinitionSource.class); load(loader); } //使用注解加载 if (isComponent(source)) { this.annotatedReader.register(source); return 1; } return 0; }
5、下面方法判断启动类中是否包含@Component注解，但是会神奇的发现我们的启动类中并没有该注解，继续更进发现MergedAnnotations类传入了一个参数SearchStrategy.TYPE_HIERARCHY，会查找继承关系中是否包含这个注解，@SpringBootApplication-->@SpringBootConfiguration-->@Configuration-->@Component,当找到@Component注解之后，会把该对象注册到AnnotatedBeanDefinitionReader对象中
private boolean isComponent(Class<?> type) { // This has to be a bit of a guess. The only way to be sure that this type is // eligible is to make a bean definition out of it and try to instantiate it. if (MergedAnnotations.from(type, SearchStrategy.TYPE_HIERARCHY).isPresent(Component.class)) { return true; } // Nested anonymous classes are not eligible for registration, nor are groovy // closures return !type.getName().matches(".*\\$_.*closure.*") && !type.isAnonymousClass() && type.getConstructors() != null && type.getConstructors().length != 0; } /** * Register a bean from the given bean class, deriving its metadata from * class-declared annotations. * 从给定的bean class中注册一个bean对象，从注解中找到相关的元数据 */ private <T> void doRegisterBean(Class<T> beanClass, @Nullable String name, @Nullable Class<? extends Annotation>[] qualifiers, @Nullable Supplier<T> supplier, @Nullable BeanDefinitionCustomizer[] customizers) { AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(beanClass); if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) { return; } abd.setInstanceSupplier(supplier); ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd); abd.setScope(scopeMetadata.getScopeName()); String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry)); AnnotationConfigUtils.processCommonDefinitionAnnotations(abd); if (qualifiers != null) { for (Class<? extends Annotation> qualifier : qualifiers) { if (Primary.class == qualifier) { abd.setPrimary(true); } else if (Lazy.class == qualifier) { abd.setLazyInit(true); } else { abd.addQualifier(new AutowireCandidateQualifier(qualifier)); } } } if (customizers != null) { for (BeanDefinitionCustomizer customizer : customizers) { customizer.customize(abd); } } BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName); definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry); BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry); } /** * Register the given bean definition with the given bean factory. * 注册主类，如果有别名可以设置别名 */ public static void registerBeanDefinition( BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry) throws BeanDefinitionStoreException { // Register bean definition under primary name. String beanName = definitionHolder.getBeanName(); registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition()); // Register aliases for bean name, if any. String[] aliases = definitionHolder.getAliases(); if (aliases != null) { for (String alias : aliases) { registry.registerAlias(beanName, alias); } } } //@SpringBootApplication @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 {} //@SpringBootConfiguration @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Configuration public @interface SpringBootConfiguration {} //@Configuration @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Component public @interface Configuration {}
当看完上述代码之后，只是完成了启动对象的注入，自动装配还没有开始，下面开始进入到自动装配。
6、自动装配入口，从刷新容器开始
@Override public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. prepareRefresh(); // Tell the subclass to refresh the internal bean factory. ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. prepareBeanFactory(beanFactory); try { // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. // 此处是自动装配的入口 invokeBeanFactoryPostProcessors(beanFactory); }
7、在invokeBeanFactoryPostProcessors方法中完成bean的实例化和执行
/** * Instantiate and invoke all registered BeanFactoryPostProcessor beans, * respecting explicit order if given. * <p>Must be called before singleton instantiation. */ protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) { //开始执行beanFactoryPostProcessor对应实现类,需要知道的是beanFactoryPostProcessor是spring的扩展接口，在刷新容器之前，该接口可以用来修改bean元数据信息 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())); } }
8、查看invokeBeanFactoryPostProcessors的具体执行方法
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<>(); //开始遍历三个内部类，如果属于BeanDefinitionRegistryPostProcessor子类，加入到bean注册的集合，否则加入到regularPostProcessors for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) { if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) { BeanDefinitionRegistryPostProcessor registryProcessor = (BeanDefinitionRegistryPostProcessor) postProcessor; registryProcessor.postProcessBeanDefinitionRegistry(registry); registryProcessors.add(registryProcessor); } else { regularPostProcessors.add(postProcessor); } } // Do not initialize FactoryBeans here: We need to leave all regular beans // uninitialized to let the bean factory post-processors apply to them! // Separate between BeanDefinitionRegistryPostProcessors that implement // PriorityOrdered, Ordered, and the rest. List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>(); // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered. //通过BeanDefinitionRegistryPostProcessor获取到对应的处理类“org.springframework.context.annotation.internalConfigurationAnnotationProcessor”，但是需要注意的是这个类在springboot中搜索不到，这个类的完全限定名在AnnotationConfigEmbeddedWebApplicationContext中，在进行初始化的时候会装配几个类，在创建AnnotatedBeanDefinitionReader对象的时候会将该类注册到bean对象中，此处可以看到internalConfigurationAnnotationProcessor为bean名称，容器中真正的类是ConfigurationClassPostProcessor String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); //首先执行类型为PriorityOrdered的BeanDefinitionRegistryPostProcessor //PriorityOrdered类型表明为优先执行 for (String ppName : postProcessorNames) { if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) { //获取对应的bean currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); //用来存储已经执行过的BeanDefinitionRegistryPostProcessor processedBeans.add(ppName); } } sortPostProcessors(currentRegistryProcessors, beanFactory); registryProcessors.addAll(currentRegistryProcessors); //开始执行装配逻辑 invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); currentRegistryProcessors.clear(); // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered. //其次执行类型为Ordered的BeanDefinitionRegistryPostProcessor //Ordered表明按顺序执行 postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); for (String ppName : postProcessorNames) { if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) { currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); processedBeans.add(ppName); } } sortPostProcessors(currentRegistryProcessors, beanFactory); registryProcessors.addAll(currentRegistryProcessors); invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); currentRegistryProcessors.clear(); // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear. //循环中执行类型不为PriorityOrdered，Ordered类型的BeanDefinitionRegistryPostProcessor boolean reiterate = true; while (reiterate) { reiterate = false; postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); for (String ppName : postProcessorNames) { if (!processedBeans.contains(ppName)) { currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); processedBeans.add(ppName); reiterate = true; } } sortPostProcessors(currentRegistryProcessors, beanFactory); registryProcessors.addAll(currentRegistryProcessors); invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry); currentRegistryProcessors.clear(); } // Now, invoke the postProcessBeanFactory callback of all processors handled so far. //执行父类方法，优先执行注册处理类 invokeBeanFactoryPostProcessors(registryProcessors, beanFactory); //执行有规则处理类 invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory); } else { // Invoke factory processors registered with the context instance. invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory); } // Do not initialize FactoryBeans here: We need to leave all regular beans // uninitialized to let the bean factory post-processors apply to them! String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false); // Separate between BeanFactoryPostProcessors that implement PriorityOrdered, // Ordered, and the rest. List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>(); List<String> orderedPostProcessorNames = new ArrayList<>(); List<String> nonOrderedPostProcessorNames = new ArrayList<>(); for (String ppName : postProcessorNames) { if (processedBeans.contains(ppName)) { // skip - already processed in first phase above } else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) { priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class)); } else if (beanFactory.isTypeMatch(ppName, Ordered.class)) { orderedPostProcessorNames.add(ppName); } else { nonOrderedPostProcessorNames.add(ppName); } } // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered. sortPostProcessors(priorityOrderedPostProcessors, beanFactory); invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory); // Next, invoke the BeanFactoryPostProcessors that implement Ordered. List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size()); for (String postProcessorName : orderedPostProcessorNames) { orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class)); } sortPostProcessors(orderedPostProcessors, beanFactory); invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory); // Finally, invoke all other BeanFactoryPostProcessors. List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size()); for (String postProcessorName : nonOrderedPostProcessorNames) { nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class)); } invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory); // Clear cached merged bean definitions since the post-processors might have // modified the original metadata, e.g. replacing placeholders in values... beanFactory.clearMetadataCache(); }
9、开始执行自动配置逻辑（启动类指定的配置，非默认配置），可以通过debug的方式一层层向里进行查找，会发现最终会在ConfigurationClassParser类中，此类是所有配置类的解析类，所有的解析逻辑在parser.parse(candidates)中
public void parse(Set<BeanDefinitionHolder> configCandidates) { for (BeanDefinitionHolder holder : configCandidates) { BeanDefinition bd = holder.getBeanDefinition(); try { //是否是注解类 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); } } //执行配置类 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 { if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) { return; } 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 { //循环处理bean,如果有父类，则处理父类，直至结束 sourceClass = doProcessConfigurationClass(configClass, sourceClass); } while (sourceClass != null); this.configurationClasses.put(configClass, configClass); }
10、继续跟进doProcessConfigurationClass方法，此方式是支持注解配置的核心逻辑
/** * Apply processing and build a complete {@link ConfigurationClass} by reading the * annotations, members and methods from the source class. This method can be called * multiple times as relevant sources are discovered. * @param configClass the configuration class being build * @param sourceClass a source class * @return the superclass, or {@code null} if none found or previously processed */ @Nullable protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass) throws IOException { //处理内部类逻辑，由于传来的参数是启动类，并不包含内部类，所以跳过 if (configClass.getMetadata().isAnnotated(Component.class.getName())) { // Recursively process any member (nested) classes first processMemberClasses(configClass, sourceClass); } // Process any @PropertySource annotations //针对属性配置的解析 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 // 这里是根据启动类@ComponentScan注解来扫描项目中的bean 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 //遍历项目中的bean，如果是注解定义的bean，则进一步解析 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)) { //递归解析，所有的bean,如果有注解，会进一步解析注解中包含的bean parse(bdCand.getBeanClassName(), holder.getBeanName()); } } } } // Process any @Import annotations //递归解析，获取导入的配置类，很多情况下，导入的配置类中会同样包含导入类注解 processImports(configClass, sourceClass, getImports(sourceClass), true); // Process any @ImportResource annotations //解析@ImportResource配置类 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 //处理@Bean注解修饰的类 Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass); for (MethodMetadata methodMetadata : beanMethods) { configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass)); } // Process default methods on interfaces // 处理接口中的默认方法 processInterfaces(configClass, sourceClass); // Process superclass, if any //如果该类有父类，则继续返回，上层方法判断不为空，则继续递归执行 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; }
11、查看获取配置类的逻辑
processImports(configClass, sourceClass, getImports(sourceClass), true); /** * Returns {@code @Import} class, considering all meta-annotations. */ private Set<SourceClass> getImports(SourceClass sourceClass) throws IOException { Set<SourceClass> imports = new LinkedHashSet<>(); Set<SourceClass> visited = new LinkedHashSet<>(); collectImports(sourceClass, imports, visited); return imports; } ------------------ /** * Recursively collect all declared {@code @Import} values. Unlike most * meta-annotations it is valid to have several {@code @Import}s declared with * different values; the usual process of returning values from the first * meta-annotation on a class is not sufficient. * <p>For example, it is common for a {@code @Configuration} class to declare direct * {@code @Import}s in addition to meta-imports originating from an {@code @Enable} * annotation. * 看到所有的bean都以导入的方式被加载进去 */ private void collectImports(SourceClass sourceClass, Set<SourceClass> imports, Set<SourceClass> visited) throws IOException { if (visited.add(sourceClass)) { for (SourceClass annotation : sourceClass.getAnnotations()) { String annName = annotation.getMetadata().getClassName(); if (!annName.equals(Import.class.getName())) { collectImports(annotation, imports, visited); } } imports.addAll(sourceClass.getAnnotationAttributes(Import.class.getName(), "value")); } }
12、继续回到ConfigurationClassParser中的parse方法中的最后一行,继续跟进该方法：
this.deferredImportSelectorHandler.process() ------------- public void process() { List<DeferredImportSelectorHolder> deferredImports = this.deferredImportSelectors; this.deferredImportSelectors = null; try { if (deferredImports != null) { DeferredImportSelectorGroupingHandler handler = new DeferredImportSelectorGroupingHandler(); deferredImports.sort(DEFERRED_IMPORT_COMPARATOR); deferredImports.forEach(handler::register); handler.processGroupImports(); } } finally { this.deferredImportSelectors = new ArrayList<>(); } } --------------- public void processGroupImports() { for (DeferredImportSelectorGrouping grouping : this.groupings.values()) { grouping.getImports().forEach(entry -> { ConfigurationClass configurationClass = this.configurationClasses.get( entry.getMetadata()); try { processImports(configurationClass, asSourceClass(configurationClass), asSourceClasses(entry.getImportClassName()), false); } catch (BeanDefinitionStoreException ex) { throw ex; } catch (Throwable ex) { throw new BeanDefinitionStoreException( "Failed to process import candidates for configuration class [" + configurationClass.getMetadata().getClassName() + "]", ex); } }); } } ------------ /** * Return the imports defined by the group. * @return each import with its associated configuration class */ public Iterable<Group.Entry> getImports() { for (DeferredImportSelectorHolder deferredImport : this.deferredImports) { this.group.process(deferredImport.getConfigurationClass().getMetadata(), deferredImport.getImportSelector()); } return this.group.selectImports(); } } ------------ public DeferredImportSelector getImportSelector() { return this.importSelector; } ------------ @Override public void process(AnnotationMetadata annotationMetadata, DeferredImportSelector deferredImportSelector) { Assert.state(deferredImportSelector instanceof AutoConfigurationImportSelector, () -> String.format("Only %s implementations are supported, got %s", AutoConfigurationImportSelector.class.getSimpleName(), deferredImportSelector.getClass().getName())); AutoConfigurationEntry autoConfigurationEntry = ((AutoConfigurationImportSelector) deferredImportSelector) .getAutoConfigurationEntry(getAutoConfigurationMetadata(), annotationMetadata); this.autoConfigurationEntries.add(autoConfigurationEntry); for (String importClassName : autoConfigurationEntry.getConfigurations()) { this.entries.putIfAbsent(importClassName, annotationMetadata); } }
如何理解springboot中的starter？
使用spring+springmvc框架进行开发的时候，如果需要引入mybatis框架，那么需要在xml中定义需要的bean对象，这个过程很明显是很麻烦的，如果需要引入额外的其他组件，那么也需要进行复杂的配置，因此在springboot中引入了starter
starter就是一个jar包，写一个@Configuration的配置类，将这些bean定义在其中，然后再starter包的META-INF/spring.factories中写入配置类，那么springboot程序在启动的时候就会按照约定来加载该配置类
开发人员只需要将相应的starter包依赖进应用中，进行相关的属性配置，就可以进行代码开发，而不需要单独进行bean对象的配置
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