Spring IOC 源码阅读资源加载和注册

   上面讲到，Spring在查找到资源以后，在BeanDefinitionReader的loadBeanDefinitions（String location）方法中，接着就调用了int loadCount = loadBeanDefinitions(resources);

   这个方法间接的调用了子类XmlBeanDifinitionReader的loadBeanDefinitions(EncodedResource encodedResource)方法：

/** * Load bean definitions from the specified XML file. * @param encodedResource the resource descriptor for the XML file, * allowing to specify an encoding to use for parsing the file * @return the number of bean definitions found * @throws BeanDefinitionStoreException in case of loading or parsing errors */public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {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);}//当前的资源正在加载--我猜的if (!currentResources.add(encodedResource)) {throw new BeanDefinitionStoreException("Detected cyclic loading of " + encodedResource + " - check your import definitions!");}try {InputStream inputStream = encodedResource.getResource().getInputStream();try {InputSource inputSource = new InputSource(inputStream);if (encodedResource.getEncoding() != null) {inputSource.setEncoding(encodedResource.getEncoding());}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();}}}

上述方法调用了doLoadBeanDefinitions(InputSource inputSource, Resource resource)方法：

 

/** * Actually load bean definitions from the specified XML file. * @param inputSource the SAX InputSource to read from * @param resource the resource descriptor for the XML file * @return the number of bean definitions found * @throws BeanDefinitionStoreException in case of loading or parsing errors */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);}}

在上面的方法中将xml人间解析成了document对象，然后调用了registerBeanDefinitions(Document doc, Resource resource)方法：

/** * Register the bean definitions contained in the given DOM document. * Called by <code>loadBeanDefinitions</code>. * <p>Creates a new instance of the parser class and invokes * <code>registerBeanDefinitions</code> on it. * @param doc the DOM document * @param resource the resource descriptor (for context information) * @return the number of bean definitions found * @throws BeanDefinitionStoreException in case of parsing errors * @see #loadBeanDefinitions * @see #setDocumentReaderClass * @see BeanDefinitionDocumentReader#registerBeanDefinitions */public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();documentReader.setEnvironment(this.getEnvironment());int countBefore = getRegistry().getBeanDefinitionCount();documentReader.registerBeanDefinitions(doc, createReaderContext(resource));return getRegistry().getBeanDefinitionCount() - countBefore;}

在上面的方法中先创建了一个DocumentReader对象，然后调用DefaultBeanDifinitionDocumentReader的registerBeanDefinitions(Document doc, XmlReaderContext readerContext)方法，此方法调用了下面的方法

/** * Register each bean definition within the given root {@code <beans/>} element. * @throws IllegalStateException if {@code <beans profile="..."} attribute is present * and Environment property has not been set * @see #setEnvironment */protected void doRegisterBeanDefinitions(Element root) {String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);if (StringUtils.hasText(profileSpec)) {Assert.state(this.environment != null, "environment property must not be null");String[] specifiedProfiles = StringUtils.tokenizeToStringArray(profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);if (!this.environment.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 = createHelper(readerContext, root, parent);preProcessXml(root);parseBeanDefinitions(root, this.delegate);postProcessXml(root);this.delegate = parent;}

在这个方法中创建了解析beandefinition的委托对象，实际上所有的解析都是在这个委托对象中完成的。

再看上面的方法间接调用了下面的DefaultBeanDifinitionDocumentReader方法：

/** * Process the given bean element, parsing the bean definition * and registering it with the registry. */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));}}

上面红色的的两个方法一个是解析得到BeanDefinitionHolder对象，此对象持有BeanDefinition对象和bean的别名，id等信息。一个方法是注册解析得到的BeanDefinition。

 下面看看在BeanDefinitionParserDeleget类中的解析方法，

/** * Parses the supplied <code><bean></code> element. May return <code>null</code> * if there were errors during parse. Errors are reported to the * {@link org.springframework.beans.factory.parsing.ProblemReporter}. */public BeanDefinitionHolder parseBeanDefinitionElement(Element ele) {return parseBeanDefinitionElement(ele, null);}/** * Parses the supplied <code><bean></code> element. May return <code>null</code> * if there were errors during parse. Errors are reported to the * {@link org.springframework.beans.factory.parsing.ProblemReporter}. */public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {//这里取得<bean>中定义的 id name和 aliase的值

                  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, MULTI_VALUE_ATTRIBUTE_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);}                  //这个方法是对bean元素的详细解析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;}

看看详细的解析方法： parseBeanDefinitionElement( Element ele, String beanName, BeanDefinition containingBean)

/** * Parse the bean definition itself, without regard to name or aliases. May return * <code>null</code> if problems occurred during the parsing of the bean definition. */public AbstractBeanDefinition parseBeanDefinitionElement(Element ele, String beanName, BeanDefinition containingBean) {this.parseState.push(new BeanEntry(beanName));                  //取得class name的定义，这里指读取<bean>中设置的class的名字，记录到BeanDefinition中，并不涉及对象的实例化过程，实例化实际上是在以来注入的时候完成的String className = null;if (ele.hasAttribute(CLASS_ATTRIBUTE)) {className = ele.getAttribute(CLASS_ATTRIBUTE).trim();}try {String parent = null;if (ele.hasAttribute(PARENT_ATTRIBUTE)) {parent = ele.getAttribute(PARENT_ATTRIBUTE);}AbstractBeanDefinition bd = createBeanDefinition(className, parent);                           //对当前的Bean元素进行属性解析，并设置description的信息 parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));                           //从名字可以看出。这里是对各种<bean>元素的信息进行解析的地方parseMetaElements(ele, bd);parseLookupOverrideSubElements(ele, bd.getMethodOverrides());parseReplacedMethodSubElements(ele, bd.getMethodOverrides());                           //解析<bean>的构造函数parseConstructorArgElements(ele, bd);//解析bean的property设置

                           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;}

上面主要关注红色的两个方法，一个是创建了BeanDefinition，一个是解析详细的bean的属性设置。

创建BeanDefinition是在调用了类BeanDefinitionReaderUtils.createBeanDefinition(parentName, className, this.readerContext.getBeanClassLoader());方法

/** * Create a new GenericBeanDefinition for the given parent name and class name, * eagerly loading the bean class if a ClassLoader has been specified. * @param parentName the name of the parent bean, if any * @param className the name of the bean class, if any * @param classLoader the ClassLoader to use for loading bean classes * (can be <code>null</code> to just register bean classes by name) * @return the bean definition * @throws ClassNotFoundException if the bean class could not be loaded */public static AbstractBeanDefinition createBeanDefinition(String parentName, String className, 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;}

再看详细解析bean的属性定义的方法：

 

/** * Parse property sub-elements of the given bean element. */public void parsePropertyElements(Element beanEle, BeanDefinition bd) {NodeList nl = beanEle.getChildNodes();for (int i = 0; i < nl.getLength(); i++) {Node node = nl.item(i);if (isCandidateElement(node) && nodeNameEquals(node, PROPERTY_ELEMENT)) {parsePropertyElement((Element) node, bd);}}}

 

/** * Parse a property element. */public void parsePropertyElement(Element ele, BeanDefinition bd) {//取得property的名字

                  String propertyName = ele.getAttribute(NAME_ATTRIBUTE);if (!StringUtils.hasLength(propertyName)) {error("Tag 'property' must have a 'name' attribute", ele);return;}this.parseState.push(new PropertyEntry(propertyName));try {      //如果在同一个Bean中已经有同名的property存在，则不进行解析，直接返回，也就是说，在同一个bean中的相同property设置，只有第一个起作用

                          if (bd.getPropertyValues().contains(propertyName)) {error("Multiple 'property' definitions for property '" + propertyName + "'", ele);return;}                           //这里是解析property的地方，返回的对象对应对bean定义的property属性设置的解析结果，这个解析结果会被封装到PropertyValue中

Object val = parsePropertyValue(ele, bd, propertyName);PropertyValue pv = new PropertyValue(propertyName, val);parseMetaElements(ele, pv);pv.setSource(extractSource(ele));bd.getPropertyValues().addPropertyValue(pv);}finally {this.parseState.pop();}}

下面这个方法是去的Property元素的值，也许是MAP,LIST SET或者其他ref对象

/** * Get the value of a property element. May be a list etc. * Also used for constructor arguments, "propertyName" being null in this case. */public Object parsePropertyValue(Element ele, BeanDefinition bd, String propertyName) {String elementName = (propertyName != null) ?"<property> element for property '" + propertyName + "'" :"<constructor-arg> element";// Should only have one child element: ref, value, list, etc.NodeList nl = ele.getChildNodes();Element subElement = null;for (int i = 0; i < nl.getLength(); i++) {Node node = nl.item(i);if (node instanceof Element && !nodeNameEquals(node, DESCRIPTION_ELEMENT) &&!nodeNameEquals(node, META_ELEMENT)) {// Child element is what we're looking for.if (subElement != null) {error(elementName + " must not contain more than one sub-element", ele);}else {subElement = (Element) node;}}}                  //这里判断property的属性是ref还是value，不允许同时是ref和valueboolean hasRefAttribute = ele.hasAttribute(REF_ATTRIBUTE);boolean hasValueAttribute = ele.hasAttribute(VALUE_ATTRIBUTE);if ((hasRefAttribute && hasValueAttribute) ||((hasRefAttribute || hasValueAttribute) && subElement != null)) {error(elementName +" is only allowed to contain either 'ref' attribute OR 'value' attribute OR sub-element", ele);}                  //如果是ref，创建一个ref的数据对象RuntimeBeanReference 这个对象封装 了ref的信息if (hasRefAttribute) {String refName = ele.getAttribute(REF_ATTRIBUTE);if (!StringUtils.hasText(refName)) {error(elementName + " contains empty 'ref' attribute", ele);}RuntimeBeanReference ref = new RuntimeBeanReference(refName);ref.setSource(extractSource(ele));return ref;}                  //如果是value，创建一个value的数据对象TypeStringValue，这个对象封装了value信息

else if (hasValueAttribute) {TypedStringValue valueHolder = new TypedStringValue(ele.getAttribute(VALUE_ATTRIBUTE));valueHolder.setSource(extractSource(ele));return valueHolder;}//如果有子元素，对子元素解析，这里是对Map、List、Set、Property等元素解析

                 else if (subElement != null) {return parsePropertySubElement(subElement, bd);}else {// Neither child element nor "ref" or "value" attribute found.error(elementName + " must specify a ref or value", ele);return null;}}

上述解析过程可简单的看成是

1、XmlBeanDefinitionReader读取资源，

2、交给DefaultBeanDefinitionDocumentReader对象解析成Document对象，

3、然后DefaultBeanDefinitionDocumentReader对象委托给BeanDefinitionParserDelegate对象解析成BeanDefinitionHoler对象。

4、得到返回的BeanDefunitionHolder对象后调用BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());方法进行注册。

getReaderContext().getRegistry()这里得到的是DefaultListableBeanFactory。在AbstarctXmlApplicationContext的创建XmlBeandefinitionReader的地方可以看到：

XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

 

DefaultListableBeanFactory中注册的地方

 

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);}}                   注册的地方需要同步，保持一致性synchronized (this.beanDefinitionMap) {                           //这里检查是不是有相同名字的BeanDefinition已经存在于IOC容器了，如果有相同的名字的BeanDefinition，但又不允许覆盖，会抛出异常

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 {//这是正常的注册BeanDefinition的过程，把Bean的名字存入到BeanDefinitionNames的同时，beanName作为Map的Key，吧BeanDefinition作为value存入到IOC容器的BeanDefinitionMap中

                                     this.beanDefinitionNames.add(beanName);this.frozenBeanDefinitionNames = null;}this.beanDefinitionMap.put(beanName, beanDefinition);}resetBeanDefinition(beanName);}

上面的代码可以看出IOC容器是作为一个Map实现的。看看DefaultListableBeanFactory中有关容器定义

 

 /** Map from dependency type to corresponding autowired value */
 private final Map<Class<?>, Object> resolvableDependencies = new HashMap<Class<?>, Object>();

 /** 这个就是存放BeanDefinition的容器MAP */
 private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>();

 /** 存放单例的类的名字 */
 private final Map<Class<?>, String[]> singletonBeanNamesByType = new ConcurrentHashMap<Class<?>, String[]>();

 /** Map of non-singleton bean names keyed by bean class */
 private final Map<Class<?>, String[]> nonSingletonBeanNamesByType = new ConcurrentHashMap<Class<?>, String[]>();

 /** 容器中的beanName集合 */
 private final List<String> beanDefinitionNames = new ArrayList<String>();

容器启动时候完成的事情就已经全部分析完成了，类的实例化是在依赖注入或根据配置在容器启动的时候完成的。容器启动加载完成后，就可以再getBean方法调用的时候去使用了。