spring源码阅读(1)bean解析
public class Test { public static void main(String[] args) throws Exception { BeanFactory beanFactory = new XmlBeanFactory(new ClassPathResource("bean.xml")); Person person = beanFactory.getBean("person",Person.class); person.info();
} }
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> <bean id="person" class="com.wh.Person"> <property name="age" value="25"></property> <property name="name" value="wanghong"></property> </bean> </beans>
从资源文件得到DOM对象
先看看XmlBeanFactory所处的地位。
XmlBeanFactory构造函数中调用了XmlBeanDefinitionReader类型的reader属性提供的方法this.reader.loadBeanDefinitions(resource)。这句代码是整个资源加载的切入点。
public class XmlBeanFactory extends DefaultListableBeanFactory { private final XmlBeanDefinitionReader reader; public XmlBeanFactory(Resource resource) throws BeansException { this(resource, (BeanFactory)null); } public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException { super(parentBeanFactory); this.reader = new XmlBeanDefinitionReader(this);
//利用XmlBeanDefinitionReader类开始资源加载 this.reader.loadBeanDefinitions(resource); } }
XmlBeanFactory扩展了DefaultListableBeanFactory,使用XmlBeanDefinitionReader从XML配置文件中读取bean的定义。忽略其他的细节,我们先来看看这个配置文件(是一种Resource)是如何被加载的。跟踪进去,进入XmlBeanDefinitionReader#loadBeanDefinitions方法,然后扑面而来的是下面这个重要的方法。
public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException { //1.封装资源文件。当进入XmlBeanDefinitionReader后首先对参数Resource使用EncodedResource类进行封装
//EncodedResource类主要用于对资源文件的编码进行处理。其中主要逻辑体现在getReader()方法中。
Assert.notNull(encodedResource, "EncodedResource must not be null"); if (logger.isInfoEnabled()) { logger.info("Loading XML bean definitions from " + encodedResource.getResource()); } Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get(); if (currentResources == null) { currentResources = new HashSet<EncodedResource>(4); this.resourcesCurrentlyBeingLoaded.set(currentResources); } if (!currentResources.add(encodedResource)) { throw new BeanDefinitionStoreException( "Detected cyclic loading of " + encodedResource + " - check your import definitions!"); } try { //2获取输入流,从Resource中获取对应的InputStream并构造InputResource InputStream inputStream = encodedResource.getResource().getInputStream(); try { InputSource inputSource = new InputSource(inputStream); if (encodedResource.getEncoding() != null) { inputSource.setEncoding(encodedResource.getEncoding()); } //3通过构造的InputResource实例和Resource实例继续调用函数doLoadBeanDefinitions return doLoadBeanDefinitions(inputSource, encodedResource.getResource()); } finally { inputStream.close(); } } catch (IOException ex) { throw new BeanDefinitionStoreException( "IOException parsing XML document from " + encodedResource.getResource(), ex); } finally { currentResources.remove(encodedResource); if (currentResources.isEmpty()) { this.resourcesCurrentlyBeingLoaded.remove(); } } }
成员变量resourcesCurrentlyBeingLoaded是一个ThreadLocal,所以资源文件多线程加载是安全的,同时使用HashSet判断资源文件的循环加载,接下来就是读取我们的资源文件了,
其中InputSource表征一个XML实体的输入源,包装了几个字段。
从输入源InputSource中获得表示该XML文件的Document对象,后续就是操纵这个document。
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException { try { int validationMode = getValidationModeForResource(resource); Document doc = this.documentLoader.loadDocument( inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware()); return registerBeanDefinitions(doc, resource); } 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); } }
在上面冗长的代码中假如不考虑异常类的代码,其实只做了三件事,这三件事每一件都必不可少。
1.获取对XML文件的验证模式
2.加载XML文件,并得到对应的Document。
3.根据返回的Document注册bean信息。
然后就是根据Spring的"spring-beans" DTD(就是我们在配置文件开始制定的命名空间和location),注册该DOM对象里面的bean。
protected void doRegisterBeanDefinitions(Element root) { String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE); if (StringUtils.hasText(profileSpec)) { String[] specifiedProfiles = StringUtils.tokenizeToStringArray( profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS); if (!getEnvironment().acceptsProfiles(specifiedProfiles)) { return; } } // 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(this.readerContext, root, parent); preProcessXml(root); parseBeanDefinitions(root, this.delegate); postProcessXml(root); this.delegate = parent; }
通过上面代码我们看到了处理流程,首先是对profile的处理,然后开始进行解析,可是当我们跟进preProcessXml(root)或者postProcessXml(root)发现
代码是空的,就像面向对象设计方法学上常说的一句话,一个类要么是面向继承的设计的,要么就用final修饰。在DefaultBeanDefinitionDocumentReader中没有用final修饰,
所以是面向继承的。这两个方法是为子类而设计的,这是模板方法模式。如果子类需要在Bean解析前后做一些处理的话,那么只需要重写这两个方法就可以了。
后续的工作就是解析这里的DOM对象,从根节点开始,处理每个node,每个元素可以是默认命名空间有的(如"import", "alias", "bean"),也可以是自定义的。
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); } }
重点是看bean的定义是如何实现的,其他的先不关注。
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); } }
接下来就是具体处理一个bean定义的过程。
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)); } }
接下来委派给BeanDefinitionParserDelegate来专门解析XML里的bean定义,如果深究下去太多了,暂时先略过其中的细节,解析成功后返回一个 BeanDefinitionHolder.
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) { String id = ele.getAttribute(ID_ATTRIBUTE); String nameAttr = ele.getAttribute(NAME_ATTRIBUTE); List<String> aliases = new ArrayList<String>(); if (StringUtils.hasLength(nameAttr)) { String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, BEAN_NAME_DELIMITERS); aliases.addAll(Arrays.asList(nameArr)); } String beanName = id; if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) { beanName = aliases.remove(0); if (logger.isDebugEnabled()) { logger.debug("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.isDebugEnabled()) { logger.debug("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; }
当我们bean definition解析之后,就要进行注册,注册到bean factory中。
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 aliase : aliases) { registry.registerAlias(beanName, aliase); } } }
这项工作由实现了BeanDefinitionRegistry接口的DefaultListableBeanFactory类实现的。
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException { Assert.hasText(beanName, "Bean name must not be empty"); Assert.notNull(beanDefinition, "BeanDefinition must not be null"); if (beanDefinition instanceof AbstractBeanDefinition) { try { ((AbstractBeanDefinition) beanDefinition).validate(); } catch (BeanDefinitionValidationException ex) { throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Validation of bean definition failed", ex); } } synchronized (this.beanDefinitionMap) { Object oldBeanDefinition = this.beanDefinitionMap.get(beanName); if (oldBeanDefinition != null) { if (!this.allowBeanDefinitionOverriding) { throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName + "': There is already [" + oldBeanDefinition + "] bound."); } else { if (this.logger.isInfoEnabled()) { this.logger.info("Overriding bean definition for bean '" + beanName + "': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]"); } } } else { this.beanDefinitionNames.add(beanName); this.frozenBeanDefinitionNames = null; } this.beanDefinitionMap.put(beanName, beanDefinition); resetBeanDefinition(beanName); } }
可以看到就是把bean的定义存储在一个ConcurrentHashMap中,同时对于重复定义的bean也会报错,同时也把 bean definition name 有序的存在beanDefinitionNames数组中。