Spring 源码解读继续。java
本文是 Spring 系列第八篇,若是小伙伴们还没阅读过本系列前面的文章,建议先看看,这有助于更好的理解本文。node
不知道小伙伴们是否还记得,在前面咱们讲 Spring 文档加载的时候,涉及到以下一段源码:spring
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException { try { Document doc = doLoadDocument(inputSource, resource); int count = registerBeanDefinitions(doc, resource); if (logger.isDebugEnabled()) { logger.debug("Loaded " + count + " bean definitions from " + resource); } return count; } catch (BeanDefinitionStoreException ex) { throw ex; } catch (SAXParseException ex) { throw new XmlBeanDefinitionStoreException(resource.getDescription(), "Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex); } catch (SAXException ex) { throw new XmlBeanDefinitionStoreException(resource.getDescription(), "XML document from " + resource + " is invalid", ex); } catch (ParserConfigurationException ex) { throw new BeanDefinitionStoreException(resource.getDescription(), "Parser configuration exception parsing XML from " + resource, ex); } catch (IOException ex) { throw new BeanDefinitionStoreException(resource.getDescription(), "IOException parsing XML document from " + resource, ex); } catch (Throwable ex) { throw new BeanDefinitionStoreException(resource.getDescription(), "Unexpected exception parsing XML document from " + resource, ex); } }
这段代码就两个核心方法:express
BeanDefinition 是什么,有什么做用,松哥在以前的 Spring 源码第四弹!深刻理解 BeanDefinition 一文中已经作过介绍,这里就再也不赘述。ide
本文咱们就来看看 Document 对象是如何一步一步加载成 BeanDefinition 的。函数
咱们就从 registerBeanDefinitions 方法开始看起:源码分析
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException { BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader(); int countBefore = getRegistry().getBeanDefinitionCount(); documentReader.registerBeanDefinitions(doc, createReaderContext(resource)); return getRegistry().getBeanDefinitionCount() - countBefore; }
这里经过调用 createBeanDefinitionDocumentReader 方法获取到一个 BeanDefinitionDocumentReader 的实例,具体的对象则是 DefaultBeanDefinitionDocumentReader,也就是说接下来调用 DefaultBeanDefinitionDocumentReader#registerBeanDefinitions 进行解析。继续来看该方法的定义:post
@Override public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) { this.readerContext = readerContext; doRegisterBeanDefinitions(doc.getDocumentElement()); }
这里又调用到了 doRegisterBeanDefinitions 方法继续完成注册:ui
protected void doRegisterBeanDefinitions(Element root) { // Any nested <beans> elements will cause recursion in this method. In // order to propagate and preserve <beans> default-* attributes correctly, // keep track of the current (parent) delegate, which may be null. Create // the new (child) delegate with a reference to the parent for fallback purposes, // then ultimately reset this.delegate back to its original (parent) reference. // this behavior emulates a stack of delegates without actually necessitating one. 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; } } } preProcessXml(root); parseBeanDefinitions(root, this.delegate); postProcessXml(root); this.delegate = parent; }
这个方法流程比较简单,首先检查了一下有没有 profile 须要处理(若是有人不清楚 Spring 中的 profile,能够在公众号后台回复 spring5 获取松哥录制的免费的 Spring 入门教程)。处理完 profile 以后,接下来就是解析了,解析有一个前置处理方法 preProcessXml 和后置处理方法 postProcessXml,不过这两个方法默认都是空方法,真正的解析方法是 parseBeanDefinitions:this
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) { if (delegate.isDefaultNamespace(root)) { 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)) { parseDefaultElement(ele, delegate); } else { delegate.parseCustomElement(ele); } } } } else { delegate.parseCustomElement(root); } }
在该方法中进行节点的解析,最终会来到 parseDefaultElement 方法中。咱们一块儿来看下该方法:
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); } }
终于来到期盼已久的 parseDefaultElement 方法中了。
在该方法中,咱们能够看到,节点一共被分为了四大类:
每个节点都好理解,由于咱们在开发中可能多多少少都有用过,须要注意的是,若是是 beans 节点,又会再次调用 doRegisterBeanDefinitions 方法进行递归解析,源码上面还给了一个注释 recurse,意思就是递归。
四种类型的节点解析,咱们就从 bean 的解析看起吧,由于 beans 节点是咱们最经常使用的节点,这个搞清楚了,另外三个节点就能够触类旁通了。
咱们来看 processBeanDefinition 方法:
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) { BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele); if (bdHolder != null) { bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder); try { // Register the final decorated instance. 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)); } }
在这段代码中,首先调用代理类 BeanDefinitionParserDelegate 对元素进行解析,解析的结果会保存在 bdHolder 中,也就是 bean 节点中配置的元素 class、id、name 等属性,在通过这一步的解析以后,都会保存到 bdHolder 中。
若是 bdHolder 不为空,那么接下来对子节点的属性继续解析,同时对 bdHolder 进行注册,最终发出事件,通知这个 bean 节点已经加载完了。
如此看来,整个解析的核心过程应该在 delegate.parseBeanDefinitionElement(ele) 方法中,追踪该方法的执行,咱们最终来到这里:
@Nullable public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) { String id = ele.getAttribute(ID_ATTRIBUTE); String nameAttr = ele.getAttribute(NAME_ATTRIBUTE); List<String> aliases = new ArrayList<>(); if (StringUtils.hasLength(nameAttr)) { String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS); aliases.addAll(Arrays.asList(nameArr)); } String beanName = id; if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) { beanName = aliases.remove(0); if (logger.isTraceEnabled()) { logger.trace("No XML 'id' specified - using '" + beanName + "' as bean name and " + aliases + " as aliases"); } } if (containingBean == null) { checkNameUniqueness(beanName, aliases, ele); } AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean); if (beanDefinition != null) { if (!StringUtils.hasText(beanName)) { try { if (containingBean != null) { beanName = BeanDefinitionReaderUtils.generateBeanName( beanDefinition, this.readerContext.getRegistry(), true); } else { beanName = this.readerContext.generateBeanName(beanDefinition); // Register an alias for the plain bean class name, if still possible, // if the generator returned the class name plus a suffix. // This is expected for Spring 1.2/2.0 backwards compatibility. String beanClassName = beanDefinition.getBeanClassName(); if (beanClassName != null && beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() && !this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) { aliases.add(beanClassName); } } if (logger.isTraceEnabled()) { logger.trace("Neither XML 'id' nor 'name' specified - " + "using generated bean name [" + beanName + "]"); } } catch (Exception ex) { error(ex.getMessage(), ele); return null; } } String[] aliasesArray = StringUtils.toStringArray(aliases); return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray); } return null; }
这个方法中所做的事情咱们能够大体分为 5 个步骤:
在这一层面主要完成了对 id 和 name 的处理,若是用户没有给 bean 定义名称的话,则生成一个默认的名称,至于其余属性的解析,则主要是在 parseBeanDefinitionElement 方法中完成的。
@Nullable public AbstractBeanDefinition parseBeanDefinitionElement( Element ele, String beanName, @Nullable BeanDefinition containingBean) { this.parseState.push(new BeanEntry(beanName)); String className = null; if (ele.hasAttribute(CLASS_ATTRIBUTE)) { className = ele.getAttribute(CLASS_ATTRIBUTE).trim(); } String parent = null; if (ele.hasAttribute(PARENT_ATTRIBUTE)) { parent = ele.getAttribute(PARENT_ATTRIBUTE); } try { 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; } catch (ClassNotFoundException ex) { error("Bean class [" + className + "] not found", ele, ex); } catch (NoClassDefFoundError err) { error("Class that bean class [" + className + "] depends on not found", ele, err); } catch (Throwable ex) { error("Unexpected failure during bean definition parsing", ele, ex); } finally { this.parseState.pop(); } return null; }
能够看到,bean 节点中全部的属性都解析了,有的是咱们平常常见的属性,有的是咱们不常见的甚至历来都没见到过的,不管哪一种状况,如今所有都解析了。解析完成后,将得到的 GenericBeanDefinition 返回。
这里有一些属性的解析可能比较冷门,这个我一会说,还有一些比较常规,例如 parseBeanDefinitionAttributes 方法用来解析各类各样的节点属性,这些节点属性可能你们都比较熟悉,咱们一块儿来看下:
public AbstractBeanDefinition parseBeanDefinitionAttributes(Element ele, String beanName, @Nullable BeanDefinition containingBean, AbstractBeanDefinition bd) { if (ele.hasAttribute(SINGLETON_ATTRIBUTE)) { error("Old 1.x 'singleton' attribute in use - upgrade to 'scope' declaration", ele); } else if (ele.hasAttribute(SCOPE_ATTRIBUTE)) { bd.setScope(ele.getAttribute(SCOPE_ATTRIBUTE)); } else if (containingBean != null) { // Take default from containing bean in case of an inner bean definition. bd.setScope(containingBean.getScope()); } if (ele.hasAttribute(ABSTRACT_ATTRIBUTE)) { bd.setAbstract(TRUE_VALUE.equals(ele.getAttribute(ABSTRACT_ATTRIBUTE))); } String lazyInit = ele.getAttribute(LAZY_INIT_ATTRIBUTE); if (isDefaultValue(lazyInit)) { lazyInit = this.defaults.getLazyInit(); } bd.setLazyInit(TRUE_VALUE.equals(lazyInit)); String autowire = ele.getAttribute(AUTOWIRE_ATTRIBUTE); bd.setAutowireMode(getAutowireMode(autowire)); if (ele.hasAttribute(DEPENDS_ON_ATTRIBUTE)) { String dependsOn = ele.getAttribute(DEPENDS_ON_ATTRIBUTE); bd.setDependsOn(StringUtils.tokenizeToStringArray(dependsOn, MULTI_VALUE_ATTRIBUTE_DELIMITERS)); } String autowireCandidate = ele.getAttribute(AUTOWIRE_CANDIDATE_ATTRIBUTE); if (isDefaultValue(autowireCandidate)) { String candidatePattern = this.defaults.getAutowireCandidates(); if (candidatePattern != null) { String[] patterns = StringUtils.commaDelimitedListToStringArray(candidatePattern); bd.setAutowireCandidate(PatternMatchUtils.simpleMatch(patterns, beanName)); } } else { bd.setAutowireCandidate(TRUE_VALUE.equals(autowireCandidate)); } if (ele.hasAttribute(PRIMARY_ATTRIBUTE)) { bd.setPrimary(TRUE_VALUE.equals(ele.getAttribute(PRIMARY_ATTRIBUTE))); } if (ele.hasAttribute(INIT_METHOD_ATTRIBUTE)) { String initMethodName = ele.getAttribute(INIT_METHOD_ATTRIBUTE); bd.setInitMethodName(initMethodName); } else if (this.defaults.getInitMethod() != null) { bd.setInitMethodName(this.defaults.getInitMethod()); bd.setEnforceInitMethod(false); } if (ele.hasAttribute(DESTROY_METHOD_ATTRIBUTE)) { String destroyMethodName = ele.getAttribute(DESTROY_METHOD_ATTRIBUTE); bd.setDestroyMethodName(destroyMethodName); } else if (this.defaults.getDestroyMethod() != null) { bd.setDestroyMethodName(this.defaults.getDestroyMethod()); bd.setEnforceDestroyMethod(false); } if (ele.hasAttribute(FACTORY_METHOD_ATTRIBUTE)) { bd.setFactoryMethodName(ele.getAttribute(FACTORY_METHOD_ATTRIBUTE)); } if (ele.hasAttribute(FACTORY_BEAN_ATTRIBUTE)) { bd.setFactoryBeanName(ele.getAttribute(FACTORY_BEAN_ATTRIBUTE)); } return bd; }
能够看到,这里解析的节点属性,从上往下,依次是:
这些属性做用你们都比较熟悉。由于平常用的多一些。
前面提到的解析中,lookup-method、replace-method、以及 qualifier 等属性可能你们平常都不多用到,甚至没有据说过,若是用都没用过,那源码确定很差理解,因此接下来松哥会录制一个视频,来和你们讲一讲这些冷门属性的使用,而后咱们再继续深刻解析这里的 parseMetaElements、parseLookupOverrideSubElements 等方法。
有了 BeanDefinitionHolder 以后,接下来 Bean 的生成就很容易了。
你们回顾以下两篇文章来理解有了 BeanDefinition 以后,如何转化为具体的 Bean:
好啦,今天的文章就先说这么多~