一、spring的IOC控制反转：控制反转——Spring通过一种称作控制反转（IOC）的技术促进了松耦合。当应用了IOC，一个对象依赖的其它对象会通过被动的方式传递进来，而不是这个对象自己创建或者查找依赖对象。说白了就是原本需要手动去创建和管理的对象，现在交给容器了。在容器的基础上，实现对象的控制。这个方式也很好的减少了开发者在框架上面的时间，更多关注点在业务逻辑上面。
二、这表博客的主要目的是研究，bean容器的初始化，会在最基本的bean初始化作源码的解析和分析。如何存在不妥当的地方，还请指出！
三、BeanFactory是spring的核心，通过工厂的模式来创建和使用bean。
四、我们都知道spring的bean初始化，依赖xml文件来实现的，所以这里重点讲解XmlBeanFactory的初始化过程。可能有人会问为什么不是ApplicationContext，相对于ApplicationContext，XmlBeanFactory是基础的bean初始化过程，后续我会单独将ApplicationContext又做了哪些动作。
五、源码解读
1）创建xml配置文件spring-bean.xml（这里省略User,，重点不在这里）
<?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="user" class="com.pinnet.customLabel.User"/> </beans>
2）开始创建对象
package com.pinnet.bean; import org.springframework.beans.factory.xml.XmlBeanFactory; import org.springframework.core.io.ClassPathResource; import org.springframework.core.io.Resource; public class Test { public static void main(String[] args) { //读取资源 Resource resource = new ClassPathResource("spring-bean.xml"); //初始化容器 new XmlBeanFactory(resource); } }
3）初始化XmlBeanFactory
private final XmlBeanDefinitionReader reader; public XmlBeanFactory(Resource resource) throws BeansException { this(resource, (BeanFactory)null); } public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException { super(parentBeanFactory); //用XmlBeanDefinitionReader，来进行加载 this.reader = new XmlBeanDefinitionReader(this); //解析资源 this.reader.loadBeanDefinitions(resource); }
4）loadBeanDefinitions
public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
//包装成EncodedResource return this.loadBeanDefinitions(new EncodedResource(resource)); } public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException { Assert.notNull(encodedResource, "EncodedResource must not be null"); if (this.logger.isInfoEnabled()) { this.logger.info("Loading XML bean definitions from " + encodedResource.getResource()); } Set<EncodedResource> currentResources = (Set)this.resourcesCurrentlyBeingLoaded.get(); if (currentResources == null) { currentResources = new HashSet(4); this.resourcesCurrentlyBeingLoaded.set(currentResources); } if (!((Set)currentResources).add(encodedResource)) { throw new BeanDefinitionStoreException("Detected cyclic loading of " + encodedResource + " - check your import definitions!"); } else { int var6; try {
//转换成InputStream流 InputStream inputStream = encodedResource.getResource().getInputStream(); try { InputSource inputSource = new InputSource(inputStream); if (encodedResource.getEncoding() != null) { inputSource.setEncoding(encodedResource.getEncoding()); } //进一步解析 var6 = this.doLoadBeanDefinitions(inputSource, encodedResource.getResource()); } finally { inputStream.close(); } } catch (IOException var15) { throw new BeanDefinitionStoreException("IOException parsing XML document from " + encodedResource.getResource(), var15); } finally { ((Set)currentResources).remove(encodedResource); if (((Set)currentResources).isEmpty()) { this.resourcesCurrentlyBeingLoaded.remove(); } } return var6; } }
5）doLoadBeanDefinitions
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException { try { int validationMode = this.getValidationModeForResource(resource);
//读取xml为doc Document doc = this.documentLoader.loadDocument(inputSource, this.getEntityResolver(), this.errorHandler, validationMode, this.isNamespaceAware());
//注册BeanDefinition return this.registerBeanDefinitions(doc, resource); } catch (BeanDefinitionStoreException var5) { throw var5; } catch (SAXParseException var6) { throw new XmlBeanDefinitionStoreException(resource.getDescription(), "Line " + var6.getLineNumber() + " in XML document from " + resource + " is invalid", var6); } catch (SAXException var7) { throw new XmlBeanDefinitionStoreException(resource.getDescription(), "XML document from " + resource + " is invalid", var7); } catch (ParserConfigurationException var8) { throw new BeanDefinitionStoreException(resource.getDescription(), "Parser configuration exception parsing XML from " + resource, var8); } catch (IOException var9) { throw new BeanDefinitionStoreException(resource.getDescription(), "IOException parsing XML document from " + resource, var9); } catch (Throwable var10) { throw new BeanDefinitionStoreException(resource.getDescription(), "Unexpected exception parsing XML document from " + resource, var10); } }
6）registerBeanDefinitions
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) { this.readerContext = readerContext; this.logger.debug("Loading bean definitions"); Element root = doc.getDocumentElement(); BeanDefinitionParserDelegate delegate = this.createHelper(readerContext, root);
//此方法用于提供子类处理之用 this.preProcessXml(root); this.parseBeanDefinitions(root, delegate);
//此方法用于提供子类处理之用 this.postProcessXml(root); }
7）parseBeanDefinitions（这一部分就是解析过程了）
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)) {
//默认标签解析 this.parseDefaultElement(ele, delegate); } else {
//自定义标签解析（这里后面讲，这个也是非常重要的拓展功能） delegate.parseCustomElement(ele); } } } } else { delegate.parseCustomElement(root); } }
8）parseDefaultElement（默认标签解析，这里关注bean）
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) { if (delegate.nodeNameEquals(ele, "import")) { this.importBeanDefinitionResource(ele); } else if (delegate.nodeNameEquals(ele, "alias")) { this.processAliasRegistration(ele); } else if (delegate.nodeNameEquals(ele, "bean")) { this.processBeanDefinition(ele, delegate); } }
9）processBeanDefinition
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) { //这里主要是解析过程 BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele); if (bdHolder != null) { bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder); try { //这里注册bean到beanDefinitionMap，后面会看到 BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, this.getReaderContext().getRegistry()); } catch (BeanDefinitionStoreException var5) { this.getReaderContext().error("Failed to register bean definition with name '" + bdHolder.getBeanName() + "'", ele, var5); } this.getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder)); } }
a、parseBeanDefinitionElement
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele) { return this.parseBeanDefinitionElement(ele, (BeanDefinition)null); } public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) { String id = ele.getAttribute("id"); String nameAttr = ele.getAttribute("name"); List<String> aliases = new ArrayList(); if (StringUtils.hasLength(nameAttr)) { String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, ",; "); aliases.addAll((Collection)Arrays.asList(nameArr)); } String beanName = id; if (!StringUtils.hasText(id) && !aliases.isEmpty()) { beanName = (String)aliases.remove(0); if (this.logger.isDebugEnabled()) { this.logger.debug("No XML 'id' specified - using '" + beanName + "' as bean name and " + aliases + " as aliases"); } } if (containingBean == null) { //检查id和别名是否重复 this.checkNameUniqueness(beanName, aliases, ele); } //解析过程 AbstractBeanDefinition beanDefinition = this.parseBeanDefinitionElement(ele, beanName, containingBean); if (beanDefinition != null) { if (!StringUtils.hasText(beanName)) { try { if (containingBean != null) { beanName = BeanDefinitionReaderUtils.generateBeanName(beanDefinition, this.readerContext.getRegistry(), true); } else { //生成beanName 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); } } if (this.logger.isDebugEnabled()) { this.logger.debug("Neither XML 'id' nor 'name' specified - using generated bean name [" + beanName + "]"); } } catch (Exception var9) { this.error(var9.getMessage(), ele); return null; } } String[] aliasesArray = StringUtils.toStringArray(aliases); //将别名和beanName放入BeanDefinitionHolder return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray); } else { return null; } }
parseBeanDefinitionElement（进一步解析过程，可以自己查看源码，这里不讲解）
public AbstractBeanDefinition parseBeanDefinitionElement(Element ele, String beanName, BeanDefinition containingBean) { this.parseState.push(new BeanEntry(beanName)); String className = null; if (ele.hasAttribute("class")) { className = ele.getAttribute("class").trim(); } try { String parent = null; if (ele.hasAttribute("parent")) { parent = ele.getAttribute("parent"); } //创建GenericBeanDefinition AbstractBeanDefinition bd = this.createBeanDefinition(className, parent); //解析bean上面的默认元素 this.parseBeanDefinitionAttributes(ele, beanName, containingBean, bd); bd.setDescription(DomUtils.getChildElementValueByTagName(ele, "description")); //meta this.parseMetaElements(ele, bd); //lookup-method this.parseLookupOverrideSubElements(ele, bd.getMethodOverrides()); //replaced-method this.parseReplacedMethodSubElements(ele, bd.getMethodOverrides()); //constructor-arg this.parseConstructorArgElements(ele, bd); //property this.parsePropertyElements(ele, bd); //qualifier this.parseQualifierElements(ele, bd); bd.setResource(this.readerContext.getResource()); bd.setSource(this.extractSource(ele)); //所有解析过后的元素全部放在AbstractBeanDefinition里面 AbstractBeanDefinition var8 = bd; return var8; } catch (ClassNotFoundException var13) { this.error("Bean class [" + className + "] not found", ele, var13); } catch (NoClassDefFoundError var14) { this.error("Class that bean class [" + className + "] depends on not found", ele, var14); } catch (Throwable var15) { this.error("Unexpected failure during bean definition parsing", ele, var15); } finally { this.parseState.pop(); } return null; }
b、registerBeanDefinition（将AbstractBeanDefinition的相关数据放入beanDefinitionMap）
public static void registerBeanDefinition(BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry) throws BeanDefinitionStoreException { String beanName = definitionHolder.getBeanName(); registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition()); String[] aliases = definitionHolder.getAliases(); if (aliases != null) { String[] var7 = aliases; int var6 = aliases.length; for(int var5 = 0; var5 < var6; ++var5) { String aliase = var7[var5]; registry.registerAlias(beanName, aliase); } } }
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 var6) { throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Validation of bean definition failed", var6); } } Map var3 = this.beanDefinitionMap; 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."); } 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; } //将beanName和beanDefinition形成键值对的形式，保存在Map中 this.beanDefinitionMap.put(beanName, beanDefinition); this.resetBeanDefinition(beanName); } }
六、好了，这就是源码的实现过程，中间省略了很多的判定和实现过程。主要的流程，基本上就是这样。这里重点注意几个点，也是对流程的梳理
1）初始化XmlBeanFactory，需要注意XmlBeanDefinitionReader：这是整个解读过程的关键
2）然后就是字符集包装，然后形成流EncodedResource、inputSource
3）解析xml，基本上是通过spring的DefaultDocumentLoader实现的，通过对Document文档的解析来实现标签和元素的解析
4）判断是否是默认标签是通过xml的Namespace来实现的，默认Namespace的读取目录是通过DefaultNamespaceHandlerResolver来实现的，也就是读取spring.handlers和spring.schemas，后续会讲到这两个文件的作用
public boolean isDefaultNamespace(String namespaceUri) { return !StringUtils.hasLength(namespaceUri) || "http://www.springframework.org/schema/beans".equals(namespaceUri); }
protected NamespaceHandlerResolver createDefaultNamespaceHandlerResolver() { return new DefaultNamespaceHandlerResolver(this.getResourceLoader().getClassLoader()); }
spring.handlers
http\://www.springframework.org/schema/p=org.springframework.beans.factory.xml.SimplePropertyNamespaceHandler http\://www.springframework.org/schema/util=org.springframework.beans.factory.xml.UtilNamespaceHandler
spring.schemas
http\://www.springframework.org/schema/beans/spring-beans-2.0.xsd=org/springframework/beans/factory/xml/spring-beans-2.0.xsd http\://www.springframework.org/schema/beans/spring-beans-2.5.xsd=org/springframework/beans/factory/xml/spring-beans-2.5.xsd http\://www.springframework.org/schema/beans/spring-beans-3.0.xsd=org/springframework/beans/factory/xml/spring-beans-3.0.xsd http\://www.springframework.org/schema/beans/spring-beans.xsd=org/springframework/beans/factory/xml/spring-beans-3.0.xsd http\://www.springframework.org/schema/tool/spring-tool-2.0.xsd=org/springframework/beans/factory/xml/spring-tool-2.0.xsd http\://www.springframework.org/schema/tool/spring-tool-2.5.xsd=org/springframework/beans/factory/xml/spring-tool-2.5.xsd http\://www.springframework.org/schema/tool/spring-tool-3.0.xsd=org/springframework/beans/factory/xml/spring-tool-3.0.xsd http\://www.springframework.org/schema/tool/spring-tool.xsd=org/springframework/beans/factory/xml/spring-tool-3.0.xsd http\://www.springframework.org/schema/util/spring-util-2.0.xsd=org/springframework/beans/factory/xml/spring-util-2.0.xsd http\://www.springframework.org/schema/util/spring-util-2.5.xsd=org/springframework/beans/factory/xml/spring-util-2.5.xsd http\://www.springframework.org/schema/util/spring-util-3.0.xsd=org/springframework/beans/factory/xml/spring-util-3.0.xsd http\://www.springframework.org/schema/util/spring-util.xsd=org/springframework/beans/factory/xml/spring-util-3.0.xsd
5）解析bean标签，是生产一个GenericBeanDefinition这个类是继承AbstractBeanDefinition生产BeanDefinition的过程其实就是讲标签里面的元素进行解析放入的过程
6）注册的过程是放在DefaultListableBeanFactory里面的beanDefinitionMap，是不是有点奇怪过程并没有DefaultListableBeanFactory。在源码的9）中使用了BeanDefinitionRegistry ，而这个BeanDefinitionRegistry 也是我们最开始使用的XmlBeanFactory，但是XmlBeanFactory，并没有太多的实现。看来一个结构：
其实最开始调用XmlBeanFactory的时候就已经使用了DefaultListableBeanFactory，值不够是继承关系而已。所以这里基本上所有的数据都在DefaultListableBeanFactory里面了
7）最后解析过程就到这里，主要数据全部在DefaultListableBeanFactory的beanDefinitionMap里面。
8）注意一点，别名的加载过程也很重要，这里不多介绍，多想法自己查看源码
七、容器的初始化基本上就是这样了，主要是梳理流程和spring在IOC的控制中做了什么。