Spring 源码学习笔记(一)容器的基础结构

<?xml version="1.0" encoding="UTF-8"?>
<beans>
	<bean id="book" class="domain.SimpleBook"/>
</beans>

public class SimpleBook {

	private int id;

	private String name = "Default Name";

}

public static void main(String[] args) {
	ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("config.xml");
	SimpleBook book = context.getBean(SimpleBook.class);
	System.out.println(book.getName());
}

Default Name

public ClassPathXmlApplicationContext(
		String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
		throws BeansException {
	super(parent);
	// 注释 1.1 获取资源文件
	setConfigLocations(configLocations);
	if (refresh) {
		refresh();
	}
}

public AbstractApplicationContext() {
	this.resourcePatternResolver = getResourcePatternResolver();
}

public AbstractApplicationContext(@Nullable ApplicationContext parent) {
	this();
	setParent(parent);
}

protected ResourcePatternResolver getResourcePatternResolver() {
	return new PathMatchingResourcePatternResolver(this);
}

public void setConfigLocations(@Nullable String... locations) {
	if (locations != null) {
		Assert.noNullElements(locations, "Config locations must not be null");
		// 注释 1.2 将配置资源路径放入 configLocations 数组中
		this.configLocations = new String[locations.length];
		for (int i = 0; i < locations.length; i++) {
			this.configLocations[i] = resolvePath(locations[i]).trim();
		}
	}
	else {
		this.configLocations = null;
	}
}

protected String resolvePath(String path) {
	return getEnvironment().resolveRequiredPlaceholders(path);
}

public String replacePlaceholders(String value, PlaceholderResolver placeholderResolver) {
	Assert.notNull(value, "'value' must not be null");
    // 用返回的值替换格式为{@code ${name}}的所有占位符
	return parseStringValue(value, placeholderResolver, null);
}

<!-- 测试环境配置文件 -->
<beans profile="test">
    <context:property-placeholder location="classpath:test/*.properties, classpath:common/*.properties" />
</beans>

<!-- 生产环境配置文件 -->
<beans profile="production">
    <context:property-placeholder location="classpath:production/*.properties, classpath:common/*.properties" />
</beans>

<!-- 开发环境配置文件 -->
<beans profile="development">
    <context:property-placeholder location="classpath:dev/*.properties, classpath:common/*.properties" />
</beans>

<context-param>
    <param-name>spring.profiles.active</param-name>
    <param-value>test</param-value>
</context-param>

context.getEnvironment().setActiveProfiles("test");

/**
 * A description of a JavaBeans Property that allows us to avoid a dependency on
 * {@code java.beans.PropertyDescriptor}. The {@code java.beans} package
 * is not available in a number of environments (e.g. Android, Java ME), so this is
 * desirable for portability of Spring's core conversion facility.
 *
 **/

它允许我们避免对 {@code java.bean . propertydescriptor}的依赖。

因为 {@code java。bean} package 在许多环境中都不可用(例如 Android、Java ME)，因此这对于 Spring 的核心转换工具的可移植性来说是非常理想的。

private final MutablePropertySources propertySources = new MutablePropertySources()

private final ConfigurablePropertyResolver propertyResolver =
			new PropertySourcesPropertyResolver(this.propertySources);
            
public AbstractEnvironment() {
	customizePropertySources(this.propertySources);
}

protected void customizePropertySources(MutablePropertySources propertySources) {
	propertySources.addLast(new MapPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));
	propertySources.addLast(new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));
}

((MutablePropertySources)((StandardEnvironment)context.environment).propertySources).propertySourceList

public void refresh() throws BeansException, IllegalStateException {
	synchronized (this.startupShutdownMonitor) {
		// Prepare this context for refreshing. （为更新准备上下文，设定一些标志）
		prepareRefresh();
		// Tell the subclass to refresh the internal bean factory. （告诉子类去更新它们的 bean factory）
		// 类的注册到 bean factory 也是在这一步
		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.
			invokeBeanFactoryPostProcessors(beanFactory);
			// Register bean processors that intercept bean creation.
			registerBeanPostProcessors(beanFactory);
			// Initialize message source for this context.
			initMessageSource();
			// Initialize event multicaster for this context.
			initApplicationEventMulticaster();
			// Initialize other special beans in specific context subclasses.
			onRefresh();
			// Check for listener beans and register them.
			registerListeners();
			// Instantiate all remaining (non-lazy-init) singletons.
			finishBeanFactoryInitialization(beanFactory);
			// Last step: publish corresponding event.
			finishRefresh();
		}
		catch (BeansException ex) {
			if (logger.isWarnEnabled()) {
				logger.warn("Exception encountered during context initialization - " +
						"cancelling refresh attempt: " + ex);
			}
			// Destroy already created singletons to avoid dangling resources.
			destroyBeans();
			// Reset 'active' flag.
			cancelRefresh(ex);
			// Propagate exception to caller.
			throw ex;
		}
		finally {
			// Reset common introspection caches in Spring's core, since we
			// might not ever need metadata for singleton beans anymore...
			resetCommonCaches();
		}
	}
}

protected void prepareRefresh() {
	// Switch to active.
	// Initialize any placeholder property sources in the context environment.(空方法，等子类实现）
	initPropertySources();
	// Validate that all properties marked as required are resolvable:（校验参数）
	// see ConfigurablePropertyResolver#setRequiredProperties
	getEnvironment().validateRequiredProperties();
	// Allow for the collection of early ApplicationEvents,
	// to be published once the multicaster is available...
	this.earlyApplicationEvents = new LinkedHashSet<>();
}

public void validateRequiredProperties() {
	MissingRequiredPropertiesException ex = new MissingRequiredPropertiesException();
	for (String key : this.requiredProperties) {
		if (this.getProperty(key) == null) {
			ex.addMissingRequiredProperty(key);
		}
	}
	if (!ex.getMissingRequiredProperties().isEmpty()) {
		throw ex;
	}
}

public class CustomApplicationContext extends AnnotationConfigServletWebServerApplicationContext {
    @Override
    protected void initPropertySources() {
        super.initPropertySources();
        //把"MYSQL_HOST"作为启动的时候必须验证的环境变量
        getEnvironment().setRequiredProperties("MYSQL_HOST");
    }
}


public static void main(String[] args) {
    SpringApplication springApplication = new SpringApplication(CustomizepropertyverifyApplication.class);
    springApplication.setApplicationContextClass(CustomApplicationContext.class);
    springApplication.run(args);
}

protected final void refreshBeanFactory() throws BeansException {
	// 在更新时，如果发现已经存在，将会把之前的 bean 清理掉，并且关闭老 bean 容器
	if (hasBeanFactory()) {
		destroyBeans();
		closeBeanFactory();
	}
	try {
		DefaultListableBeanFactory beanFactory = createBeanFactory();
		beanFactory.setSerializationId(getId());
		customizeBeanFactory(beanFactory);
		// 注释 1.3 开始加载 （bean 注册）
		loadBeanDefinitions(beanFactory);
		synchronized (this.beanFactoryMonitor) {
			this.beanFactory = beanFactory;
		}
	}
	catch (IOException ex) {
		throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
	}
}

protected void customizeBeanFactory(DefaultListableBeanFactory beanFactory) {
	if (this.allowBeanDefinitionOverriding != null) {
		// 默认是 false，不允许覆盖
		beanFactory.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
	}
	if (this.allowCircularReferences != null) {
		// 默认是 false，不允许循环引用
		beanFactory.setAllowCircularReferences(this.allowCircularReferences);
	}
}

protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
	// Create a new XmlBeanDefinitionReader for the given BeanFactory.
	// 为给定的BeanFactory创建一个新的XmlBeanDefinitionReader
	XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
	// Configure the bean definition reader with this context's
	// resource loading environment.
	beanDefinitionReader.setEnvironment(this.getEnvironment());
	beanDefinitionReader.setResourceLoader(this);
	beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
	// Allow a subclass to provide custom initialization of the reader,
	// then proceed with actually loading the bean definitions.(空方法，让子类进行扩展实现）
	initBeanDefinitionReader(beanDefinitionReader);
	loadBeanDefinitions(beanDefinitionReader);
}

public int loadBeanDefinitions(String location, @Nullable Set<Resource> actualResources) throws BeanDefinitionStoreException {
    // 获取资源文件（资源加载器从路径识别资源文件）
    Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location)
    // 注释 1.6 根据资源文件加载 bean
    int count = loadBeanDefinitions(resources);		
    ···
}

public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
	// 注释 1.7 从资源文件中获取输入流
	InputStream inputStream = encodedResource.getResource().getInputStream();
	InputSource inputSource = new InputSource(inputStream);
	return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
}

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
	throws BeanDefinitionStoreException {
	// 注释 1.8 将资源文件解析成 document
	Document doc = doLoadDocument(inputSource, resource);
	// 注释 1.10 从 doc 和资源中解析元素，注册到 bean factory
	int count = registerBeanDefinitions(doc, resource);
	if (logger.isDebugEnabled()) {
		logger.debug("Loaded " + count + " bean definitions from " + resource);
	}
	return count;
}

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
	// 使用 DefaultBeanDefinitionDocumentReader 实例化 BeanDefinitionDocumentReader
	BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
	// 记录统计前 beanDefinition 的加载个数
	int countBefore = getRegistry().getBeanDefinitionCount();
	// 加载及注册 bean，这里使用注册工厂的是 DefaultListableBeanFactory
	documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
	// 记录本次加载的 BeanDefinition 个数（新值 - 旧值）
	return getRegistry().getBeanDefinitionCount() - countBefore;
}

protected void doRegisterBeanDefinitions(Element root) {
	BeanDefinitionParserDelegate parent = this.delegate;
	this.delegate = createDelegate(getReaderContext(), root, parent);
	if (this.delegate.isDefaultNamespace(root)) {
		String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
		if (StringUtils.hasText(profileSpec)) {
			String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
					profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
			// We cannot use Profiles.of(...) since profile expressions are not supported
			// in XML config. See SPR-12458 for details.
			if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
				if (logger.isDebugEnabled()) {
					logger.debug("Skipped XML bean definition file due to specified profiles [" + profileSpec +
							"] not matching: " + getReaderContext().getResource());
				}
				return;
			}
		}
	}
	// preProcess 和 postProcess 点进去会发现是空方法，这两个方法留给子类重载，体现了设计模式 - 模板方法
	preProcessXml(root);
	// 注释 1.11 核心方法，解析 doc 元素
	parseBeanDefinitions(root, this.delegate);
	postProcessXml(root);
	this.delegate = parent;
}

org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader#parseBeanDefinitions

protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
	if (delegate.isDefaultNamespace(root)) {
		// 注释 1.12 遍历 doc 中的节点列表
		NodeList nl = root.getChildNodes();
		for (int i = 0; i < nl.getLength(); i++) {
			Node node = nl.item(i);
			if (node instanceof Element) {
				Element ele = (Element) node;
				if (delegate.isDefaultNamespace(ele)) {
					// 注释 1.13 识别出默认标签的 bean 注册
					// 根据元素名称，调用不同的加载方法，注册 bean
					parseDefaultElement(ele, delegate);
				}
				else {
					delegate.parseCustomElement(ele);
				}
			}
		}
	}
	else {
		delegate.parseCustomElement(root);
	}
}

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
	if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
		importBeanDefinitionResource(ele);
	}
	else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
		processAliasRegistration(ele);
	}
	else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
		processBeanDefinition(ele, delegate);
	}
	else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
		// recurse
		doRegisterBeanDefinitions(ele);
	}
}

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
	// 注释 1.15 解析 bean 名称的元素
	BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
	if (bdHolder != null) {
		bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
		try {
			// Register the final decorated instance. （注释 1.16 注册最后修饰后的实例）
			BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
		}
		catch (BeanDefinitionStoreException ex) {
			getReaderContext().error("Failed to register bean definition with name '" +
					bdHolder.getBeanName() + "'", ele, ex);
		}
		// Send registration event.
		getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
	}
}

public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
	// 获取 ID 属性
	String id = ele.getAttribute(ID_ATTRIBUTE);
	// 获取 NAME 属性
	String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
	List<String> aliases = new ArrayList<>();
	if (StringUtils.hasLength(nameAttr)) {
		// 名称按照 , ; 进行分割
		String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
		aliases.addAll(Arrays.asList(nameArr));
	}
	String beanName = id;
	if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
		// 如果没有指定 id，将 name 的第一个值作为 id
		beanName = aliases.remove(0);
	}
	// 默认 null
	if (containingBean == null) {
		// 检查名字是否唯一，如果 id 重复了，将抛出错误
		// 内部 usedNames 是一个 HashSet，将会存储加载过的 name 和 aliases
		checkNameUniqueness(beanName, aliases, ele);
	}
	// 将公共属性放入 AbstractBeanDefinition，具体实现在子类 GenericBeanDefinition
	AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
	if (beanDefinition != null) {
		if (!StringUtils.hasText(beanName)) {
			if (containingBean != null) {
				// 如果 id 和 name 都是空，那个 spring 会给它生成一个默认的名称
				beanName = BeanDefinitionReaderUtils.generateBeanName(
						beanDefinition, this.readerContext.getRegistry(), true);
			}
			else {
				beanName = this.readerContext.generateBeanName(beanDefinition);
				String beanClassName = beanDefinition.getBeanClassName();
				if (beanClassName != null &&
						beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
						!this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
					aliases.add(beanClassName);
				    }
			    }
		    }
		}
		String[] aliasesArray = StringUtils.toStringArray(aliases);
		return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
	}
	return null;
}

public AbstractBeanDefinition parseBeanDefinitionElement(
		Element ele, String beanName, @Nullable BeanDefinition containingBean) {
    AbstractBeanDefinition bd = createBeanDefinition(className, parent);
    parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
    bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
    parseMetaElements(ele, bd);
    parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
    parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
    parseConstructorArgElements(ele, bd);
    parsePropertyElements(ele, bd);
    parseQualifierElements(ele, bd);
    bd.setResource(this.readerContext.getResource());
    bd.setSource(extractSource(ele));
    return bd;
}

public static AbstractBeanDefinition createBeanDefinition(
			@Nullable String parentName, @Nullable String className, @Nullable ClassLoader classLoader) throws ClassNotFoundException {
	GenericBeanDefinition bd = new GenericBeanDefinition();
	bd.setParentName(parentName);
	if (className != null) {
		if (classLoader != null) {
			bd.setBeanClass(ClassUtils.forName(className, classLoader));
		}
		else {
			bd.setBeanClassName(className);
		}
	}
	return bd;
}

public BeanDefinitionHolder decorateBeanDefinitionIfRequired(
			Element ele, BeanDefinitionHolder definitionHolder, @Nullable BeanDefinition containingBd) {
	// 方法中的第三个参数是父类 bean
	// 当对某个嵌套配置进行分析时，这里需要传递，是为了使用父类的 scope 属性，以备子类没设定 scope，可以使用父类的 scope 属性
	BeanDefinitionHolder finalDefinition = definitionHolder;

	// Decorate based on custom attributes first.
	NamedNodeMap attributes = ele.getAttributes();
	// 遍历所有的属性，进行属性的修饰
	for (int i = 0; i < attributes.getLength(); i++) {
		Node node = attributes.item(i);
		finalDefinition = decorateIfRequired(node, finalDefinition, containingBd);
	}

	// Decorate based on custom nested elements.
	NodeList children = ele.getChildNodes();
	// 遍历所有的子节点，修饰子元素
	for (int i = 0; i < children.getLength(); i++) {
		Node node = children.item(i);
		if (node.getNodeType() == Node.ELEMENT_NODE) {
			finalDefinition = decorateIfRequired(node, finalDefinition, containingBd);
		}
	}
	return finalDefinition;
}

public static void registerBeanDefinition(
			BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
			throws BeanDefinitionStoreException {
		// Register bean definition under primary name.
		// 注释 1.17 在 DefaultListableBeanFactory 的 beanDefinitionMap 中添加 bean 定义
		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);
			}
		}
	}

public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) {
	this.beanDefinitionMap.put(beanName, beanDefinition);
	this.beanDefinitionNames.add(beanName);
}

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