Spring 源码解析（一）IOC，终于找到一个看得懂的 JVM 内存模型了
}
if (!((Set)currentResources).add(encodedResource)) {
throw new BeanDefinitionStoreException("Detected cyclic loading of " + encodedResource + " - check your import definitions!");
} else {
int var5;
try {
InputStream inputStream = encodedResource.getResource().getInputStream();
try {
InputSource inputSource = new InputSource(inputStream);
if (encodedResource.getEncoding() != null) {
inputSource.setEncoding(encodedResource.getEncoding());
}
//在这里准备加载 BeanDefinition 了
var5 = 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 var5;
}
}
下面这里是解析 XML 加载 Bean 的方法
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException {
try {
//这里是获得 XML 文档
Document doc = this.doLoadDocument(inputSource, resource);
//这个方法是加载和注册 BeanDefinition
return this.registerBeanDefinitions(doc, resource);
} catch (BeanDefinitionStoreException var4) {
throw var4;
} catch (SAXParseException var5) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(), "Line " + var5.getLineNumber() + " in XML document from " + resource + " is invalid", var5);
} catch (SAXException var6) {
throw new XmlBeanDefinitionStoreException(resource.getDescription(), "XML document from " + resource + " is invalid", var6);
} catch (ParserConfigurationException var7) {
throw new BeanDefinitionStoreException(resource.getDescription(), "Parser configuration exception parsing XML from " + resource, var7);
} catch (IOException var8) {
throw new BeanDefinitionStoreException(resource.getDescription(), "IOException parsing XML document from " + resource, var8);
} catch (Throwable var9) {
throw new BeanDefinitionStoreException(resource.getDescription(), "Unexpected exception parsing XML document from " + resource, var9);
}
}
看这个方法：
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
//获得一个读取器
BeanDefinitionDocumentReader documentReader = this.createBeanDefinitionDocumentReader();
//获得之前的 BeanDefinition 数量
int countBefore = this.getRegistry().getBeanDefinitionCount();
//主要看这里的解析和注册
documentReader.registerBeanDefinitions(doc, this.createReaderContext(resource));
//返回总数量-之前的数量就是现在注册的 Bean 数量
return this.getRegistry().getBeanDefinitionCount() - countBefore;
}
现在到了 DefaultBeanDefinitionDocumentReader 类中，实现了 BeanDefinitionDocumentReader 接口
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
//获得读取 XML 的上下文
this.readerContext = readerContext;
this.logger.debug("Loading bean definitions");
//获得 XML 的根
Element root = doc.getDocumentElement();
//开始解析 XML
this.doRegisterBeanDefinitions(root);
}
终于开始真正解析 XML 了，这个方法从根节点开始一层一层向下解析：
protected void doRegisterBeanDefinitions(Element root) {
//这里是一个委托，而且是父委托，为什么要这样做呢？因为 XML 的解析是从 Beans 开始的，但是 Beans 的上层可能还有 Beans，这里是递归往上找到最上层的 Beans 节点。
BeanDefinitionParserDelegate parent = this.delegate;
this.delegate = this.createDelegate(this.getReaderContext(), root, parent);
if (this.delegate.isDefaultNamespace(root)) {
//这里是解析 profile 属性，profile 属性是 Beans 的，可以根据不同的环境选择不同的配置
String profileSpec = root.getAttribute("profile");
if (StringUtils.hasText(profileSpec)) {
String[] specifiedProfiles = StringUtils.tokenizeToStringArray(profileSpec, ",; ");
if (!this.getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
if (this.logger.isInfoEnabled()) {
this.logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec + "] not matching: " + this.getReaderContext().getResource());
}
return;
}
}
}
//钩子方法，前置处理
this.preProcessXml(root);
//核心解析方法
this.parseBeanDefinitions(root, this.delegate);
//钩子方法，后置处理
this.postProcessXml(root);
this.delegate = parent;
}
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
//判断是否是默认的命名空间
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;
//判断是否是默认的命名空间
if (delegate.isDefaultNamespace(ele)) {
//解析默认元素
this.parseDefaultElement(ele, delegate);
} else {
//解析自定义元素
delegate.parseCustomElement(ele);
}
}
}
} else {
delegate.parseCustomElement(root);
}
}
上面方法中会判断节点是否是默认命名空间，如果是默认的就解析默认的元素，如果不是就解析自定义元素，这里我们关键要弄清楚什么是默认的命名空间？默认的元素有哪些？哪些又是自定义元素？
这些问题，我们要了解 Spring 的配置文件：
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:aop="http://www.springframework.org/schema/aop"
xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd
http://www.springframework.org/schema/aop
http://www.springframework.org/schema/aop/spring-aop.xsd
http://www.springframework.org/schema/tx
http://www.springframework.org/schema/tx/spring-tx.xsd">
上面是大家比较熟悉的 Beans 配置，其中 xmlns 为http://www.springframework.org/schema/beans的就是默认的命名空间，其它的属于自定义命名空间.
默认命名空间中定义了 import、alias、bean、beans 这几个元素，解析默认的元素就是这几个.
而其它的命名空间中定义的元素，如：mvc、task、context、aop 等属于自定义的元素。
我们先看解析默认元素：
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
if (delegate.nodeNameEquals(ele, "import")) {
//处理 import 标签，导入资源
this.importBeanDefinitionResource(ele);
} else if (delegate.nodeNameEquals(ele, "alias")) {
//处理 alias 别名的注册
this.processAliasRegistration(ele);
} else if (delegate.nodeNameEquals(ele, "bean")) {
//处理 bean 标签
this.processBeanDefinition(ele, delegate);
} else if (delegate.nodeNameEquals(ele, "beans")) {
//注册 bean
this.doRegisterBeanDefinitions(ele);
}
}
我们知道 IOC 主要通过 bean 标签配置，那么 bean 的解析就是我们的重点。
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
//解析 BeanDefinition 出来，并封装到 BeanDefinitionHolder 中
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
//给 BeanDefinitionHolder 添加属性
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
//注册 BeanDefinition
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, this.getReaderContext().getRegistry());
} catch (BeanDefinitionStoreException var5) {
this.getReaderContext().error("Failed to register bean definition with name '" + bdHolder.getBeanName() + "'", ele, var5);
}
//发送注册事件
this.getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
这里我们主要看 BeanDefinitionHolder 的解析，其它方法先跳过，在看具体解析过程前我们先回顾下 bean 的定义：
<bean id="id 名" name="名称 1,名称 2..." class="包名+类名" scope="prototype|singleton" lazy-init="是否懒加载（true 或 false）" init-method="初始化方法" destroy-method="销毁方法">
<contructor-arg type="类型" index="位置" name="名称" value="值" ref="对象名"/>
<property name="属性名" value="值" ref="对象名">
</property>
</bean>
上面是定义一个 bean 的主要配置，接下来我们看 bean 的解析过程，这是在 BeanDefinitionParserDelegate 中完成的，类名的意思是 BeanDefinition 解析的委托。
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele) {
return this.parseBeanDefinitionElement(ele, (BeanDefinition)null);
}
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
//解析 id 属性
String id = ele.getAttribute("id");
//解析 name 属性
String nameAttr = ele.getAttribute("name");
List<String> aliases = new ArrayList();
if (StringUtils.hasLength(nameAttr)) {
//把按逗号、分号、空格分开的多个 name，添加到别名集合中
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, ",; ");
aliases.addAll(Arrays.asList(nameArr));
}
//将 id 作为 bean 的名称
String beanName = id;
if (!StringUtils.hasText(id) && !aliases.isEmpty()) {
//如果不存在 id，而 name 存在，就将别名集合的第一个 name 作为名称
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) {
this.checkNameUniqueness(beanName, aliases, ele);
}
//根据 bean 节点的配置，解析出一个基本的 BeanDefinition
AbstractBeanDefinition beanDefinition = this.parseBeanDefinitionElement(ele, beanName, containingBean);
//下面这部分主要是如果 id 和 name 都没有设置，就用 class 作为 bean 的名字
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);
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 BeanDefinition 实例封装到 BeanDefinitionHolder 中，返回
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
} else {
return null;
}
}
看看 parseBeanDefinitionElement 这个方法都做了什么
public AbstractBeanDefinition parseBeanDefinitionElement(Element ele, String beanName, BeanDefinition containingBean) {
//添加一个解析状态，这里不细讲了
this.parseState.push(new BeanEntry(beanName));
String className = null;
//将 class 先解析出来
if (ele.hasAttribute("class")) {
className = ele.getAttribute("class").trim();
}
try {
String parent = null;
//在解析 parent 属性
if (ele.hasAttribute("parent")) {
parent = ele.getAttribute("parent");
}
//通过 className 和 parent，先创建一个 BeanDefinition
AbstractBeanDefinition bd = this.createBeanDefinition(className, parent);
//解析 Bean 的各种属性
this.parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, "description"));
//解析 meta 属性
this.parseMetaElements(ele, bd);
//解析 lookup-method 属性
this.parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
//解析 replace-method 属性
this.parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
//解析 constructor-arg 节点
this.parseConstructorArgElements(ele, bd);
//解析 property 节点
this.parsePropertyElements(ele, bd);
//解析 qualifier 节点
this.parseQualifierElements(ele, bd);
bd.setResource(this.readerContext.getResource());
bd.setSource(this.extractSource(ele));
AbstractBeanDefinition var7 = bd;
return var7;
} 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;
}
这里面最有代表性的是解析 bean 的属性：
public AbstractBeanDefinition parseBeanDefinitionAttributes(Element ele, String beanName, BeanDefinition containingBean, AbstractBeanDefinition bd) {
//解析 scope 属性
if (ele.hasAttribute("singleton")) {
this.error("Old 1.x 'singleton' attribute in use - upgrade to 'scope' declaration", ele);
} else if (ele.hasAttribute("scope")) {
bd.setScope(ele.getAttribute("scope"));
} else if (containingBean != null) {
bd.setScope(containingBean.getScope());
}
//解析 abstract 属性
if (ele.hasAttribute("abstract")) {
bd.setAbstract("true".equals(ele.getAttribute("abstract")));
}
//解析 lazy-init 属性
String lazyInit = ele.getAttribute("lazy-init");
if ("default".equals(lazyInit)) {
lazyInit = this.defaults.getLazyInit();
}
bd.setLazyInit("true".equals(lazyInit));
//解析 autowire 属性
String autowire = ele.getAttribute("autowire");
bd.setAutowireMode(this.getAutowireMode(autowire));
String dependencyCheck = ele.getAttribute("dependency-check");
bd.setDependencyCheck(this.getDependencyCheck(dependencyCheck));
String autowireCandidate;
if (ele.hasAttribute("depends-on")) {
autowireCandidate = ele.getAttribute("depends-on");
bd.setDependsOn(StringUtils.tokenizeToStringArray(autowireCandidate, ",; "));
}
autowireCandidate = ele.getAttribute("autowire-candidate");
String destroyMethodName;
if (!"".equals(autowireCandidate) && !"default".equals(autowireCandidate)) {
bd.setAutowireCandidate("true".equals(autowireCandidate));
} else {
destroyMethodName = this.defaults.getAutowireCandidates();
if (destroyMethodName != null) {
String[] patterns = StringUtils.commaDelimitedListToStringArray(destroyMethodName);
bd.setAutowireCandidate(PatternMatchUtils.simpleMatch(patterns, beanName));
}
}
if (ele.hasAttribute("primary")) {
bd.setPrimary("true".equals(ele.getAttribute("primary")));
}
if (ele.hasAttribute("init-method")) {
destroyMethodName = ele.getAttribute("init-method");
if (!"".equals(destroyMethodName)) {
bd.setInitMethodName(destroyMethodName);
}
} else if (this.defaults.getInitMethod() != null) {
bd.setInitMethodName(this.defaults.getInitMethod());
bd.setEnforceInitMethod(false);
}
if (ele.hasAttribute("destroy-method")) {
destroyMethodName = ele.getAttribute("destroy-method");
bd.setDestroyMethodName(destroyMethodName);
} else if (this.defaults.getDestroyMethod() != null) {
bd.setDestroyMethodName(this.defaults.getDestroyMethod());
bd.setEnforceDestroyMethod(false);
}
if (ele.hasAttribute("factory-method")) {
bd.setFactoryMethodName(ele.getAttribute("factory-method"));
}
if (ele.hasAttribute("factory-bean")) {
bd.setFactoryBeanNa
me(ele.getAttribute("factory-bean"));
}
return bd;
}
到这里 BeanDefinition 的解析就完成了，返回了 BeanDefinitionHolder 对象， 回到前面的 processBeanDefinition 方法，接下来最重要的是注册 BeanDefinition
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
//解析 BeanDefinition 出来，并封装到 BeanDefinitionHolder 中
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
//给 BeanDefinitionHolder 添加属性
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
//注册 BeanDefinition
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, this.getReaderContext().getRegistry());
} catch (BeanDefinitionStoreException var5) {
this.getReaderContext().error("Failed to register bean definition with name '" + bdHolder.getBeanName() + "'", ele, var5);
}
//发送注册事件
this.getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
BeanDefinitionReaderUtils 类的静态方法：
public static void registerBeanDefinition(BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry) throws BeanDefinitionStoreException {
String beanName = definitionHolder.getBeanName();
//把 bean 的名称和 BeanDefinition 关联起来，这里是一个 Map 集合
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
String[] var4 = aliases;
int var5 = aliases.length;
//再把名称和别名关联起来
for(int var6 = 0; var6 < var5; ++var6) {
String alias = var4[var6];
registry.registerAlias(beanName, alias);
}
}
}
注册 BeanDefinition 是在 DefaultListableBeanFactory 这个工厂里面，开头介绍过，这个工厂是功能最强大的工厂，里面有个 Map 集合用于注册所有的 BeanDefinition：
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap(256);
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 var9) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Validation of bean definition failed", var9);
}
}
//通过 beanName 获得 BeanDefinition 实例
BeanDefinition oldBeanDefinition = (BeanDefinition)this.beanDefinitionMap.get(beanName);
if (oldBeanDefinition != null) {
//如果实例以及存在，又不允许 Bean 覆盖，就抛异常
if (!this.isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName + "': There is already [" + oldBeanDefinition + "] bound.");
}
//下面都是日志
if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
if (this.logger.isWarnEnabled()) {
this.logger.warn("Overriding user-defined bean definition for bean '" + beanName + "' with a framework-generated bean definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
}
} else if (!beanDefinition.equals(oldBeanDefinition)) {
if (this.logger.isInfoEnabled()) {
this.logger.info("Overriding bean definition for bean '" + beanName + "' with a different definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
}
} else if (this.logger.isDebugEnabled()) {
this.logger.debug("Overriding bean definition for bean '" + beanName + "' with an equivalent definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
}
//往集合里覆盖原来的 BeanDefinition
this.beanDefinitionMap.put(beanName, beanDefinition);
} else {
//这里判断有无其他 Bean 的创建过程已经开始
if (this.hasBeanCreationStarted()) {
Map var4 = this.beanDefinitionMap;
synchronized(this.beanDefinitionMap) {
//如果有，就添加 BeanDefinition
this.beanDefinitionMap.put(beanName, beanDefinition);
//添加名字到 BeanDefinition 名字集合中
List<String> updatedDefinitions = new ArrayList(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
//从手动注册的 Singleton 名字中删除该名字
if (this.manualSingletonNames.contains(beanName)) {
Set<String> updatedSingletons = new LinkedHashSet(this.manualSingletonNames);
updatedSingletons.remove(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
} else {
//如果没有开始，就在集合注册新的 BeanDefinition
this.beanDefinitionMap.put(beanName, beanDefinition);
//保存 Bean 的名字
this.beanDefinitionNames.add(beanName);
//从单例名字中删除该名字
this.manualSingletonNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (oldBeanDefinition != null || this.containsSingleton(beanName)) {
this.resetBeanDefinition(beanName);
}
}
总结下上面的所有代码，Spring 把 XML 配置文件中定义的一个个 Bean 解析出来，创建了一个个 BeanDefinition，然后都注册到 BeanFacotry 这个 IOC 容器中了。
这样可以说已经完成了 IOC 的准备工作，接下来就是 IOC 容器等待对其内部注册的 Bean 进行依赖注入，那么什么时候会发生注入呢？
也就是我们熟悉了调用 BeanFacotry 的 getBean 方法时。
如下：
ClassPathXmlApplicationContext cxt = new ClassPathXmlApplicationContext("applicationContext.xml");
Driver driver = cxt.getBean("driver", Driver.class);
来看看 getBean 方法，其具体实现在 AbstractBeanFactory 中：
public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
return this.doGetBean(name, requiredType, (Object[])null, false);
}
就是这个 doGetBean 方法：
protected <T> T doGetBean(String name, Class<T> requiredType, final Object[] args, boolean typeCheckOnly) throws BeansException {
//通过名称获得 Bean 的规范名称，主要是去掉前面的 &符号
final String beanName = this.transformedBeanName(name);
//通过名字，从缓存中获得一个单例的 Bean 实例
Object sharedInstance = this.getSingleton(beanName);
Object bean;
if (sharedInstance != null && args == null) {
if (this.logger.isDebugEnabled()) {
if (this.isSingletonCurrentlyInCreation(beanName)) {
this.logger.debug("Returning eagerly cached instance of singleton bean '" + beanName + "' that is not fully initialized yet - a consequence of a circular reference");
} else {
this.logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
}
}
//args 参数为空的情况下，创建 Bean 的对象
//如果该 Bean 是 FactoryBean，就通过 FactoryBean 创建 Bean 实例
//如果该 Bean 是普通的 Bean，就直接返回 sharedInstance 作为 Bean 实例
bean = this.getObjectForBeanInstance(sharedInstance, name, beanName, (RootBeanDefinition)null);
} else {
if (this.isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
//获得父 BeanFactory
BeanFactory parentBeanFactory = this.getParentBeanFactory();
//如果存在父 BeanFactory，并且当前 BeanFactory 中不存在此名字的 Bean
//就在父 BeanFactory 中查找 Bean
if (parentBeanFactory != null && !this.containsBeanDefinition(beanName)) {
String nameToLookup = this.originalBeanName(name);
//通过 args 参数来创建 Bean
if (args != null) {
return parentBeanFactory.getBean(nameToLookup, args);
}
//不需要 args 参数，直接通过类型创建 Bean
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
if (!typeCheckOnly) {
this.markBeanAsCreated(beanName);
}
try {
//准备创建 Bean，先创建一个根 BeanDefinition
final RootBeanDefinition mbd = this.getMergedLocalBeanDefinition(beanName);
this.checkMergedBeanDefinition(mbd, beanName, args);
//获得 Bean 的所有依赖 bean
String[] dependsOn = mbd.getDependsOn();
String[] var11;
if (dependsOn != null) {
var11 = dependsOn;
int var12 = dependsOn.length;
for(int var13 = 0; var13 < var12; ++var13) {
String dep = var11[var13];
//检查是否存在循环依赖
if (this.isDependent(beanName, dep)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
//注册所有依赖的 bean
this.registerDependentBean(dep, beanName);
//把依赖的 bean 进行初始化
this.getBean(dep);
}
}
//如果是单例，就创建单例的 bean
if (mbd.isSingleton()) {
//这里的匿名内部类是通过工厂模式，创建单例 Bean
sharedInstance = this.getSingleton(beanName, new ObjectFactory<Object>() {
public Object getObject() throws BeansException {
try {
return AbstractBeanFactory.this.createBean(beanName, mbd, args);
} catch (BeansException var2) {
AbstractBeanFactory.this.destroySingleton(beanName);
throw var2;
}
}
});
bean = this.getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
} else if (mbd.isPrototype()) {
var11 = null;
//如果是多例就直接创建对象
Object prototypeInstance;
try {
this.beforePrototypeCreation(beanName);
prototypeInstance = this.createBean(beanName, mbd, args);
} finally {
this.afterPrototypeCreation(beanName);
}
bean = this.getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
} else {
//如果 scope 属性没有配置，就通过 Scope 类获得 Bean 实例
String scopeName = mbd.getScope();
Scope scope = (Scope)this.scopes.get(scopeName);
if (scope == null) {
throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
}
try {
Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
public Object getObject() throws BeansException {
AbstractBeanFactory.this.beforePrototypeCreation(beanName);
Object var1;
try {
var1 = AbstractBeanFactory.this.createBean(beanName, mbd, args);
} finally {
AbstractBeanFactory.this.afterPrototypeCreation(beanName);
}
return var1;
}
});
bean = this.getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
} catch (IllegalStateException var21) {
throw new BeanCreationException(beanName, "Scope '" + scopeName + "' is not active for the current thread; consider defining a scoped proxy for this bean if you intend to refer to it from a singleton", var21);
}
}
} catch (BeansException var23) {
this.cleanupAfterBeanCreationFailure(beanName);
throw var23;
}
}
//将 Bean 转换为需要的类型
if (requiredType != null && bean != null && !requiredType.isInstance(bean)) {
try {
return this.getTypeConverter().convertIfNecessary(bean, requiredType);
} catch (TypeMismatchException var22) {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Failed to convert bean '" + name + "' to required type '" + ClassUtils.getQualifiedName(requiredType) + "'", var22);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
} else {
return bean;
}
}
下面就重点分析这个 createBean 了，方法在 AbstractAutowireCapableBeanFactory 类中，此类的名字意思大概是抽象的可以自动装配的 Bean 工厂，也就是说这个类和 Spring 的自动装配特性相关。
protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Creating instance of bean '" + beanName + "'");
}
RootBeanDefinition mbdToUse = mbd;
//获得 Bean 的 Class 类型，可见下面就需要用到反射了
Class<?> resolvedClass = this.resolveBeanClass(mbd, beanName, new Class[0]);
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
//设置 Bean 的 Class
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
try {
//准备 Bean 的方法重写，如 lookup-method、replace-method 这些
mbdToUse.prepareMethodOverrides();
} catch (BeanDefinitionValidationException var7) {
throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(), beanName, "Validation of method overrides failed", var7);
}
Object beanInstance;
try {
//返回 Bean 或 Bean 的代理实例
beanInstance = this.resolveBeforeInstantiation(beanName, mbdToUse);
if (beanInstance != null) {
return beanInstance;
}
} catch (Throwable var8) {
throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName, "BeanPostProcessor before instantiation of bean failed", var8);
}
//创建 Bean 的具体实现
beanInstance = this.doCreateBean(beanName, mbdToUse, args);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
}
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, Object[] args) throws BeanCreationException {
BeanWrapper instanceWrapper = null;
//如果是单例，就从缓存中取得单例的 Bean
if (mbd.isSingleton()) {
instanceWrapper = (BeanWrapper)this.factoryBeanInstanceCache.remove(beanName);
}
//如果单例为空，就创建一个单例
if (instanceWrapper == null) {
instanceWrapper = this.createBeanInstance(beanName, mbd, args);
}
//获得实例
final Object bean = instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null;
//获得实例类型
Class<?> beanType = instanceWrapper != null ? instanceWrapper.getWrappedClass() : null;
mbd.resolvedTargetType = beanType;
Object var7 = mbd.postProcessingLock;
//调用后置处理器
synchronized(mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
this.applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
} catch (Throwable var17) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Post-processing of merged bean definition failed", var17);
}
mbd.postProcessed = true;
}
}
//在容器中缓存单例的实例，防止循环引用
boolean earlySingletonExposure = mbd.isSingleton() && this.allowCircularReferences && this.isSingletonCurrentlyInCreation(beanName);
if (earlySingletonExposure) {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Eagerly caching bean '" + beanName + "' to allow for resolving potential circular references");
}
this.addSingletonFactory(beanName, new ObjectFactory<Object>() {
public Object getObject() throws BeansException {
return AbstractAutowireCapableBeanFactory.this.getEarlyBeanReference(beanName, mbd, bean);
}
});
}
Object exposedObject = bean;
try {
//给 Bean 的属性初始化
this.populateBean(beanName, mbd, instanceWrapper);
if (exposedObject != null) {
//初始化 Bean
exposedObject = this.initializeBean(beanName, exposedObject, mbd);
}
} catch (Throwable var18) {
if (var18 instanceof BeanCreationException && beanName.equals(((BeanCreationException)var18).getBeanName())) {
throw (BeanCreationException)var18;
}
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", var18);
}
if (earlySingletonExposure) {
Object earlySingletonReference = this.getSingleton(beanName, false);
if (earlySingletonReference != null) {
//当前获得的对象和正在创建的对象如果是同一个对象，就赋值完毕
if (exposedObject == bean) {
exposedObject = earlySingletonReference;
}else if (!this.allowRawInjectionDespiteWrapping && this.hasDependentBean(beanName)) {
String[] dependentBeans = this.getDependentBeans(beanName);
Set<String> actualDependentBeans = new LinkedHashSet(dependentBeans.length);
String[] var12 = dependentBeans;
int var13 = dependentBeans.length;
for(int var14 = 0; var14 < var13; ++var14) {
String dependentBean = var12[var14];
if (!this.removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
actualDependentBeans.add(dependentBean);
}
}
if (!actualDependentBeans.isEmpty()) {
throw new BeanCurrentlyInCreationException(beanName, "Bean with name '" + beanName + "' has been injected into other beans [" + StringUtils.collectionToCommaDelimitedString(actualDependentBeans) + "] in its raw version as part of a circular reference, but has eventually been wrapped. This means that said other beans do not use the final version of the bean. This is often the result of over-eager type matching - consider using 'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
try {
this.registerDisposableBeanIfNecessary(beanName, bean, mbd);
return exposedObject;
} catch (BeanDefinitionValidationException var16) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", var16);
}}
该方法的内容比较多，这里就不对所有细节进行分析了，主要看两个部分：
1、创建 Bean 的 createBeanInstance
2、初始化属性的 populateBean
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, Object[] args) {
//获得类型
Class<?> beanClass = this.resolveBeanClass(mbd, beanName, new Class[0]);
//如果类不能访问，抛异常
if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
} else if (mbd.getFactoryMethodName() != null) {
//如果存在工厂方法，就调用工厂方法创建对象
return this.instantiateUsingFactoryMethod(beanName, mbd, args);
} else {
boolean resolved = false;
boolean autowireNecessary = false;
if (args == null) {
Object var7 = mbd.constructorArgumentLock;
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