Spring源码之事务(一）— TransactionAutoConfiguration自动配置

总结：

在ConfigurationClassParser#parse（）中会对deferredImportSelectorHandler进行处理（在处理@ComponentScan 自己所写@Component的类后）
处理过程中会调用SpringFactoriesLoader#loadFactoryNames(),去查找所有jar下面META-INF/spring.factories中key为org.springframework.boot.autoconfigure.EnableAutoConfiguration的值
ConfigurationClassPostProcessor#processConfigBeanDefinitions()中loadBeanDefinitions对TransactionAutoConfiguration进行BeanDefinition的加载，并注册IOC容器

TransactionAutoConfiguration的BeanDefinition加载解析

调用链：

AbstractApplicationContext#refresh() --> AbstractApplicationContext#invokeBeanFactoryPostProcessors() --> PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors() --> PostProcessorRegistrationDelegate#invokeBeanDefinitionRegistryPostProcessors() --> ConfigurationClassPostProcessor#postProcessBeanDefinitionRegistry（）--> ConfigurationClassPostProcessor#processConfigBeanDefinitions() --> ConfigurationClassPostProcessor#parse() --> ConfigurationClassParser#process() --> ConfigurationClassParser$DeferredImportSelectorGroupingHandler#processGroupImports() --> ConfigurationClassParser#processImports() --> ConfigurationClassParser#processConfigurationClass() --> ConfigurationClassParser#doProcessConfigurationClass()

ConfigurationClassParser#parse() 对延迟ImportSelector进行处理

private final DeferredImportSelectorHandler deferredImportSelectorHandler = new DeferredImportSelectorHandler();

public void parse(Set<BeanDefinitionHolder> configCandidates) {

	this.deferredImportSelectorHandler.process();

}

调用DeferredImportSelectorGroupingHandler#processGroupImports()

public void process() {

	List<DeferredImportSelectorHolder> deferredImports = this.deferredImportSelectors;

	this.deferredImportSelectors = null;

	try {

		if (deferredImports != null) {

			DeferredImportSelectorGroupingHandler handler = new DeferredImportSelectorGroupingHandler();

			deferredImports.sort(DEFERRED_IMPORT_COMPARATOR);

			// 给ConfigurationClassParser.groupings赋值

			deferredImports.forEach(handler::register);

			// DeferredImportSelectorGroupingHandler处理

			handler.processGroupImports();

		}

	}

	finally {

		this.deferredImportSelectors = new ArrayList<>();

	}

主要handler.processGroupImports()中 grouping.getImports()会查找出所有ConfigurationClassParser$DeferredImportSelectorGroupingHandler中的imports

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, exclusionFilter),

						Collections.singleton(asSourceClass(entry.getImportClassName(), exclusionFilter)),

						exclusionFilter, false);

			}

		}

	}

}

ConfigurationClassParser$DeferredImportSelectorGroupingHandler#getImports（）

public Iterable<Group.Entry> getImports() {

	for (DeferredImportSelectorHolder deferredImport : this.deferredImports) {

		this.group.process(deferredImport.getConfigurationClass().getMetadata(),

				deferredImport.getImportSelector());

	}

	return this.group.selectImports();

}

会调用AutoConfigurationImportSelector#process（）

public void process(AnnotationMetadata annotationMetadata, DeferredImportSelector deferredImportSelector) {

	AutoConfigurationEntry autoConfigurationEntry = ((AutoConfigurationImportSelector) deferredImportSelector)

			.getAutoConfigurationEntry(annotationMetadata);

	this.autoConfigurationEntries.add(autoConfigurationEntry);

	for (String importClassName : autoConfigurationEntry.getConfigurations()) {

		this.entries.putIfAbsent(importClassName, annotationMetadata);

	}

}

会调用AutoConfigurationImportSelector#getAutoConfigurationEntry()

protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {

	List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);

	......

	return new AutoConfigurationEntry(configurations, exclusions);

}

其中AutoConfigurationImportSelector#getCandidateConfigurations()会查找所有jar下面META-INF/spring.factories，进行loadFactoryNames。

protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {

	List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),

			getBeanClassLoader());

	return configurations;

}

SpringFactoriesLoader#loadFactoryNames()

public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {

	......

	return loadSpringFactories(classLoaderToUse).getOrDefault(factoryTypeName, Collections.emptyList());

}

SpringFactoriesLoader#loadSpringFactories()

private static Map<String, List<String>> loadSpringFactories(ClassLoader classLoader) {

	result = new HashMap<>();

	try {

		Enumeration<URL> urls = classLoader.getResources(FACTORIES_RESOURCE_LOCATION);

		while (urls.hasMoreElements()) {

			URL url = urls.nextElement();

			UrlResource resource = new UrlResource(url);

			Properties properties = PropertiesLoaderUtils.loadProperties(resource);

			for (Map.Entry<?, ?> entry : properties.entrySet()) {

				String factoryTypeName = ((String) entry.getKey()).trim();

				String[] factoryImplementationNames =

						StringUtils.commaDelimitedListToStringArray((String) entry.getValue());

				for (String factoryImplementationName : factoryImplementationNames) {

					result.computeIfAbsent(factoryTypeName, key -> new ArrayList<>())

							.add(factoryImplementationName.trim());

				}

			}

		}

	}

	return result;

}

其中spring-boot-autoconfigure-XX.jar下面META-INF/spring.factories文件中就有：

org.springframework.boot.autoconfigure.EnableAutoConfiguration=org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration

附：其中ConfigurationClassParser.groupings赋值，是在ConfigurationClassParser#register（）执行的

public void register(DeferredImportSelectorHolder deferredImport) {

	Class<? extends Group> group = deferredImport.getImportSelector().getImportGroup();

	DeferredImportSelectorGrouping grouping = this.groupings.computeIfAbsent(

			(group != null ? group : deferredImport),

			key -> new DeferredImportSelectorGrouping(createGroup(group)));

	grouping.add(deferredImport);

	this.configurationClasses.put(deferredImport.getConfigurationClass().getMetadata(),

			deferredImport.getConfigurationClass());

}

loadBeanDefinitions

this.reader.loadBeanDefinitions(configClasses)进行BeanDefinition的加载，并注册到IOC容器

public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {

    this.reader.loadBeanDefinitions(configClasses);

}

巴特西

Spring源码之事务(一）— TransactionAutoConfiguration自动配置

总结：

TransactionAutoConfiguration的BeanDefinition加载解析

loadBeanDefinitions

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