Spring源码剖析3：懒加载的单例Bean获取过程分析

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转自【Spring源码分析】Bean加载流程概览

代码入口

之前写文章都会啰啰嗦嗦一大堆再开始，进入【Spring源码分析】这个板块就直接切入正题了。

很多朋友可能想看Spring源码，但是不知道应当如何入手去看，这个可以理解：Java开发者通常从事的都是Java Web的工作，对于程序员来说，一个Web项目用到Spring，只是配置一下配置文件而已，Spring的加载过程相对是不太透明的，不太好去找加载的代码入口。

下面有很简单的一段代码可以作为Spring代码加载的入口：

<pre> 1 ApplicationContext ac = new ClassPathXmlApplicationContext("spring.xml");
2 ac.getBean(XXX.class);</pre>

ClassPathXmlApplicationContext用于加载CLASSPATH下的Spring配置文件，可以看到，第二行就已经可以获取到Bean的实例了，那么必然第一行就已经完成了对所有Bean实例的加载，因此可以通过ClassPathXmlApplicationContext作为入口。为了后面便于代码阅读，先给出一下ClassPathXmlApplicationContext这个类的继承关系：

大致的继承关系是如上图所示的，由于版面的关系，没有继续画下去了，左下角的ApplicationContext应当还有一层继承关系，比较关键的一点是它是BeanFactory的子接口。

最后声明一下，本文使用的Spring版本为3.0.7，比较老，使用这个版本纯粹是因为公司使用而已。

ClassPathXmlApplicationContext存储内容

为了更理解ApplicationContext，拿一个实例ClassPathXmlApplicationContext举例，看一下里面存储的内容，加深对ApplicationContext的认识，以表格形式展现：

对象名	类 型	作 用	归属类
configResources	Resource[]	配置文件资源对象数组	ClassPathXmlApplicationContext
configLocations	String[]	配置文件字符串数组，存储配置文件路径	AbstractRefreshableConfigApplicationContext
beanFactory	DefaultListableBeanFactory	上下文使用的Bean工厂	AbstractRefreshableApplicationContext
beanFactoryMonitor	Object	Bean工厂使用的同步监视器	AbstractRefreshableApplicationContext
id	String	上下文使用的唯一Id，标识此ApplicationContext	AbstractApplicationContext
parent	ApplicationContext	父级ApplicationContext	AbstractApplicationContext
beanFactoryPostProcessors	List<BeanFactoryPostProcessor>	存储BeanFactoryPostProcessor接口，Spring提供的一个扩展点	AbstractApplicationContext
startupShutdownMonitor	Object	refresh方法和destory方法公用的一个监视器，避免两个方法同时执行	AbstractApplicationContext
shutdownHook	Thread	Spring提供的一个钩子，JVM停止执行时会运行Thread里面的方法	AbstractApplicationContext
resourcePatternResolver	ResourcePatternResolver	上下文使用的资源格式解析器	AbstractApplicationContext
lifecycleProcessor	LifecycleProcessor	用于管理Bean生命周期的生命周期处理器接口	AbstractApplicationContext
messageSource	MessageSource	用于实现国际化的一个接口	AbstractApplicationContext
applicationEventMulticaster	ApplicationEventMulticaster	Spring提供的事件管理机制中的事件多播器接口	AbstractApplicationContext
applicationListeners	Set<ApplicationListener>	Spring提供的事件管理机制中的应用监听器	AbstractApplicationContext

ClassPathXmlApplicationContext构造函数

看下ClassPathXmlApplicationContext的构造函数：

<pre> 1 public ClassPathXmlApplicationContext(String configLocation) throws BeansException { 2 this(new String[] {configLocation}, true, null);
3 }</pre>

<pre>1 public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent) 2 throws BeansException { 3
4 super(parent); 5 setConfigLocations(configLocations); 6 if (refresh) { 7 refresh(); 8 } 9 }</pre>

从第二段代码看，总共就做了三件事：

　　1、super(parent)

　　　　没什么太大的作用，设置一下父级ApplicationContext，这里是null

　　2、setConfigLocations(configLocations)

　　　　代码就不贴了，一看就知道，里面做了两件事情：

　　　　（1）将指定的Spring配置文件的路径存储到本地

　　　　（2）解析Spring配置文件路径中的${PlaceHolder}占位符，替换为系统变量中PlaceHolder对应的Value值，System本身就自带一些系统变量比如class.path、os.name、user.dir等，也可以通过System.setProperty()方法设置自己需要的系统变量

refresh()

　　　　这个就是整个Spring Bean加载的核心了，它是ClassPathXmlApplicationContext的父类AbstractApplicationContext的一个方法，顾名思义，用于刷新整个Spring上下文信息，定义了整个Spring上下文加载的流程。

refresh方法

上面已经说了，refresh()方法是整个Spring Bean加载的核心，因此看一下整个refresh()方法的定义：

<pre> 1 public void refresh() throws BeansException, IllegalStateException { 2 synchronized (this.startupShutdownMonitor) {
3 // Prepare this context for refreshing.
4 prepareRefresh();
5
6 // Tell the subclass to refresh the internal bean factory.
7 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); 8
9 // Prepare the bean factory for use in this context.
10 prepareBeanFactory(beanFactory); 11
12 try { 13 // Allows post-processing of the bean factory in context subclasses.
14 postProcessBeanFactory(beanFactory); 15
16 // Invoke factory processors registered as beans in the context.
17 invokeBeanFactoryPostProcessors(beanFactory); 18
19 // Register bean processors that intercept bean creation.
20 registerBeanPostProcessors(beanFactory); 21
22 // Initialize message source for this context.
23 initMessageSource(); 24
25 // Initialize event multicaster for this context.
26 initApplicationEventMulticaster(); 27
28 // Initialize other special beans in specific context subclasses.
29 onRefresh(); 30
31 // Check for listener beans and register them.
32 registerListeners(); 33
34 // Instantiate all remaining (non-lazy-init) singletons.
35 finishBeanFactoryInitialization(beanFactory); 36
37 // Last step: publish corresponding event.
38 finishRefresh(); 39 } 40
41 catch (BeansException ex) { 42 // Destroy already created singletons to avoid dangling resources.
43 destroyBeans(); 44
45 // Reset 'active' flag.
46 cancelRefresh(ex); 47
48 // Propagate exception to caller.
49 throw ex; 50 } 51 } 52 }</pre>

每个子方法的功能之后一点一点再分析，首先refresh()方法有几点是值得我们学习的：

　　1、方法是加锁的，这么做的原因是避免多线程同时刷新Spring上下文

　　2、尽管加锁可以看到是针对整个方法体的，但是没有在方法前加synchronized关键字，而使用了对象锁startUpShutdownMonitor，这样做有两个好处：

　　　　（1）refresh()方法和close()方法都使用了startUpShutdownMonitor对象锁加锁，这就保证了在调用refresh()方法的时候无法调用close()方法，反之亦然，避免了冲突

　　　　（2）另外一个好处不在这个方法中体现，但是提一下，使用对象锁可以减小了同步的范围，只对不能并发的代码块进行加锁，提高了整体代码运行的效率

　　3、方法里面使用了每个子方法定义了整个refresh()方法的流程，使得整个方法流程清晰易懂。这点是非常值得学习的，一个方法里面几十行甚至上百行代码写在一起，在我看来会有三个显著的问题：

　　　　（1）扩展性降低。反过来讲，假使把流程定义为方法，子类可以继承父类，可以根据需要重写方法

　　　　（2）代码可读性差。很简单的道理，看代码的人是愿意看一段500行的代码，还是愿意看10段50行的代码？

　　　　（3）代码可维护性差。这点和上面的类似但又有不同，可维护性差的意思是，一段几百行的代码，功能点不明确，不易后人修改，可能会导致“牵一发而动全身”

prepareRefresh方法

下面挨个看refresh方法中的子方法，首先是prepareRefresh方法，看一下源码：

<pre> 1 /**
2 * Prepare this context for refreshing, setting its startup date and
3 * active flag.
4 */
5 protected void prepareRefresh() { 6 this.startupDate = System.currentTimeMillis(); 7 synchronized (this.activeMonitor) {
8 this.active = true;
9 } 10
11 if (logger.isInfoEnabled()) { 12 logger.info("Refreshing " + this); 13 } 14 }</pre>

这个方法功能比较简单，顾名思义，准备刷新Spring上下文，其功能注释上写了：

1、设置一下刷新Spring上下文的开始时间

2、将active标识位设置为true

另外可以注意一下12行这句日志，这句日志打印了真正加载Spring上下文的Java类。

obtainFreshBeanFactory方法

obtainFreshBeanFactory方法的作用是获取刷新Spring上下文的Bean工厂，其代码实现为：

<pre>1 protected ConfigurableListableBeanFactory obtainFreshBeanFactory() { 2 refreshBeanFactory(); 3 ConfigurableListableBeanFactory beanFactory = getBeanFactory(); 4 if (logger.isDebugEnabled()) { 5 logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory); 6 } 7 return beanFactory; 8 }</pre>

其核心是第二行的refreshBeanFactory方法，这是一个抽象方法，有AbstractRefreshableApplicationContext和GenericApplicationContext这两个子类实现了这个方法，看一下上面ClassPathXmlApplicationContext的继承关系图即知，调用的应当是AbstractRefreshableApplicationContext中实现的refreshBeanFactory，其源码为：

<pre> 1 protected final void refreshBeanFactory() throws BeansException { 2 if (hasBeanFactory()) { 3 destroyBeans();
4 closeBeanFactory();
5 }
6 try { 7 DefaultListableBeanFactory beanFactory = createBeanFactory(); 8 beanFactory.setSerializationId(getId());
9 customizeBeanFactory(beanFactory); 10 loadBeanDefinitions(beanFactory); 11 synchronized (this.beanFactoryMonitor) { 12 this.beanFactory = beanFactory; 13 } 14 } 15 catch (IOException ex) { 16 throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex); 17 } 18 }</pre>

这段代码的核心是第7行，这行点出了DefaultListableBeanFactory这个类，这个类是构造Bean的核心类，这个类的功能会在下一篇文章中详细解读，首先给出DefaultListableBeanFactory的继承关系图：

AbstractAutowireCapableBeanFactory这个类的继承层次比较深，版面有限，就没有继续画下去了，本图基本上清楚地展示了DefaultListableBeanFactory的层次结构。

为了更清晰地说明DefaultListableBeanFactory的作用，列举一下DefaultListableBeanFactory中存储的一些重要对象及对象中的内容，DefaultListableBeanFactory基本就是操作这些对象，以表格形式说明：

对象名	类 型	作 用	归属类
aliasMap	Map<String, String>	存储Bean名称->Bean别名映射关系	SimpleAliasRegistry
singletonObjects	Map<String, Object>	存储单例Bean名称->单例Bean实现映射关系	DefaultSingletonBeanRegistry
singletonFactories	Map<String, ObjectFactory>	存储Bean名称->ObjectFactory实现映射关系	DefaultSingletonBeanRegistry
earlySingletonObjects	Map<String, Object>	存储Bean名称->预加载Bean实现映射关系	DefaultSingletonBeanRegistry
registeredSingletons	Set<String>	存储注册过的Bean名	DefaultSingletonBeanRegistry
singletonsCurrentlyInCreation	Set<String>	存储当前正在创建的Bean名	DefaultSingletonBeanRegistry
disposableBeans	Map<String, Object>	存储Bean名称->Disposable接口实现Bean实现映射关系	DefaultSingletonBeanRegistry
factoryBeanObjectCache	Map<String, Object>	存储Bean名称->FactoryBean接口Bean实现映射关系	FactoryBeanRegistrySupport
propertyEditorRegistrars	Set<PropertyEditorRegistrar>	存储PropertyEditorRegistrar接口实现集合	AbstractBeanFactory
embeddedValueResolvers	List<StringValueResolver>	存储StringValueResolver（字符串解析器）接口实现列表	AbstractBeanFactory
beanPostProcessors	List<BeanPostProcessor>	存储 BeanPostProcessor接口实现列表	AbstractBeanFactory
mergedBeanDefinitions	Map<String, RootBeanDefinition>	存储Bean名称->合并过的根Bean定义映射关系	AbstractBeanFactory
alreadyCreated	Set<String>	存储至少被创建过一次的Bean名集合	AbstractBeanFactory
ignoredDependencyInterfaces	Set<Class>	存储不自动装配的接口Class对象集合	AbstractAutowireCapableBeanFactory
resolvableDependencies	Map<Class, Object>	存储修正过的依赖映射关系	DefaultListableBeanFactory
beanDefinitionMap	Map<String, BeanDefinition>	存储Bean名称-->Bean定义映射关系	DefaultListableBeanFactory
beanDefinitionNames	List<String>	存储Bean定义名称列表	DefaultListableBeanFactory

==================================================================================

Spring是如何初始化Bean实例对象

代码入口

上文【Spring源码分析】Bean加载流程概览，比较详细地分析了Spring上下文加载的代码入口，并且在AbstractApplicationContext的refresh方法中，点出了finishBeanFactoryInitialization方法完成了对于所有非懒加载的Bean的初始化。

finishBeanFactoryInitialization方法中调用了DefaultListableBeanFactory的preInstantiateSingletons方法，本文针对preInstantiateSingletons进行分析，解读一下Spring是如何初始化Bean实例对象出来的。

DefaultListableBeanFactory的preInstantiateSingletons方法

DefaultListableBeanFactory的preInstantiateSingletons方法，顾名思义，初始化所有的单例Bean，看一下方法的定义：

<pre> 1 public void preInstantiateSingletons() throws BeansException { 2 if (this.logger.isInfoEnabled()) {
3 this.logger.info("Pre-instantiating singletons in " + this);
4 }
5 synchronized (this.beanDefinitionMap) {
6 // Iterate over a copy to allow for init methods which in turn register new bean definitions. 7 // While this may not be part of the regular factory bootstrap, it does otherwise work fine.
8 List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames);
9 for (String beanName : beanNames) { 10 RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName); 11 if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) { 12 if (isFactoryBean(beanName)) { 13 final FactoryBean factory = (FactoryBean) getBean(FACTORY_BEAN_PREFIX + beanName); 14 boolean isEagerInit; 15 if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) { 16 isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() { 17 public Boolean run() { 18 return ((SmartFactoryBean) factory).isEagerInit(); 19 } 20 }, getAccessControlContext()); 21 } 22 else { 23 isEagerInit = (factory instanceof SmartFactoryBean &&
24 ((SmartFactoryBean) factory).isEagerInit()); 25 } 26 if (isEagerInit) { 27 getBean(beanName); 28 } 29 } 30 else { 31 getBean(beanName); 32 } 33 } 34 } 35 } 36 }</pre>

这里先解释一下getMergedLocalBeanDefinition方法的含义，因为这个方法会常常看到。Bean定义公共的抽象类是AbstractBeanDefinition，普通的Bean在Spring加载Bean定义的时候，实例化出来的是GenericBeanDefinition，而Spring上下文包括实例化所有Bean用的AbstractBeanDefinition是RootBeanDefinition，这时候就使用getMergedLocalBeanDefinition方法做了一次转化，将非RootBeanDefinition转换为RootBeanDefinition以供后续操作。

解释完了getMergedLocalBeanDefinition方法的作用，第1行~第10行的代码就没什么好说的了，根据beanName拿到RootBeanDefinition而已。由于此方法实例化的是所有非懒加载的单例Bean，因此要实例化Bean，必须满足11行的三个定义：

（1）不是抽象的

（2）必须是单例的

（3）必须是非懒加载的

接着简单看一下第12行~第29行的代码，这段代码主要做的是一件事情：首先判断一下Bean是否FactoryBean的实现，接着判断Bean是否SmartFactoryBean的实现，假如Bean是SmartFactoryBean的实现并且eagerInit（这个单词字面意思是渴望加载，找不到一个好的词语去翻译，意思就是定义了这个Bean需要立即加载的意思）的话，会立即实例化这个Bean。Java开发人员不需要关注这段代码，因为SmartFactoryBean基本不会用到，我翻译一下Spring官网对于SmartFactoryBean的定义描述：

• FactoryBean接口的扩展接口。接口实现并不表示是否总是返回单独的实例对象，比如FactoryBean.isSingleton()实现返回false的情况并不清晰地表示每次返回的都是单独的实例对象
• 不实现这个扩展接口的简单FactoryBean的实现，FactoryBean.isSingleton()实现返回false总是简单地告诉我们每次返回的都是单独的实例对象，暴露出来的对象只能够通过命令访问
• 注意：这个接口是一个有特殊用途的接口，主要用于框架内部使用与Spring相关。通常，应用提供的FactoryBean接口实现应当只需要实现简单的FactoryBean接口即可，新方法应当加入到扩展接口中去

代码示例

为了后面的代码分析方便，事先我定义一个Bean：

<pre> 1 package org.xrq.action; 2
3 import org.springframework.beans.factory.BeanClassLoaderAware; 4 import org.springframework.beans.factory.BeanNameAware; 5 import org.springframework.beans.factory.InitializingBean; 6
7 public class MultiFunctionBean implements InitializingBean, BeanNameAware, BeanClassLoaderAware { 8
9 private int propertyA; 10
11 private int propertyB; 12
13 public int getPropertyA() { 14 return propertyA; 15 } 16
17 public void setPropertyA(int propertyA) { 18 this.propertyA = propertyA; 19 } 20
21 public int getPropertyB() { 22 return propertyB; 23 } 24
25 public void setPropertyB(int propertyB) { 26 this.propertyB = propertyB; 27 } 28
29 public void initMethod() { 30 System.out.println("Enter MultiFunctionBean.initMethod()"); 31 } 32
33 @Override 34 public void setBeanClassLoader(ClassLoader classLoader) { 35 System.out.println("Enter MultiFunctionBean.setBeanClassLoader(ClassLoader classLoader)"); 36 } 37
38 @Override 39 public void setBeanName(String name) { 40 System.out.println("Enter MultiFunctionBean.setBeanName(String name)"); 41 } 42
43 @Override 44 public void afterPropertiesSet() throws Exception { 45 System.out.println("Enter MultiFunctionBean.afterPropertiesSet()"); 46 } 47
48 @Override 49 public String toString() { 50 return "MultiFunctionBean [propertyA=" + propertyA + ", propertyB=" + propertyB + "]"; 51 } 52
53 }</pre>

定义对应的spring.xml：

<pre>1 <?xml version="1.0" encoding="UTF-8"?>
2 <beans xmlns="http://www.springframework.org/schema/beans"
3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
4 xsi:schemaLocation="http://www.springframework.org/schema/beans 5 http://www.springframework.or...d">
6
7 <bean id="multiFunctionBean" class="org.xrq.action.MultiFunctionBean" init-method="initMethod" />
8
9 </beans></pre>

利用这个MultiFunctionBean，我们可以用来探究Spring加载Bean的多种机制。

doGetBean方法构造Bean流程

上面把getBean之外的代码都分析了一下，看代码就可以知道，获取Bean对象实例，都是通过getBean方法，getBean方法最终调用的是DefaultListableBeanFactory的父类AbstractBeanFactory类的doGetBean方法，因此这部分重点分析一下doGetBean方法是如何构造出一个单例的Bean的。

doGetBean方法是如何构造出一个单例的Bean

看一下doGetBean方法的代码实现，比较长：

<pre> 1 protected <T> T doGetBean( 2 final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly) 3 throws BeansException { 4
5 final String beanName = transformedBeanName(name); 6 Object bean;
7
8 // Eagerly check singleton cache for manually registered singletons.
9 Object sharedInstance = getSingleton(beanName); 10 if (sharedInstance != null && args == null) {
11 if (logger.isDebugEnabled()) { 12 if (isSingletonCurrentlyInCreation(beanName)) { 13 logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
14 "' that is not fully initialized yet - a consequence of a circular reference");
15 }
16 else { 17 logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
18 }
19 }
20 bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
21 }
22
23 else { 24 // Fail if we're already creating this bean instance: 25 // We're assumably within a circular reference.
26 if (isPrototypeCurrentlyInCreation(beanName)) { 27 throw new BeanCurrentlyInCreationException(beanName); 28 }
29
30 // Check if bean definition exists in this factory.
31 BeanFactory parentBeanFactory = getParentBeanFactory(); 32 if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
33 // Not found -> check parent.
34 String nameToLookup = originalBeanName(name); 35 if (args != null) {
36 // Delegation to parent with explicit args.
37 return (T) parentBeanFactory.getBean(nameToLookup, args); 38 }
39 else { 40 // No args -> delegate to standard getBean method.
41 return parentBeanFactory.getBean(nameToLookup, requiredType); 42 }
43 }
44
45 if (!typeCheckOnly) {
46 markBeanAsCreated(beanName);
47 }
48
49 final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName); 50 checkMergedBeanDefinition(mbd, beanName, args);
51
52 // Guarantee initialization of beans that the current bean depends on.
53 String[] dependsOn = mbd.getDependsOn(); 54 if (dependsOn != null) {
55 for (String dependsOnBean : dependsOn) { 56 getBean(dependsOnBean);
57 registerDependentBean(dependsOnBean, beanName);
58 }
59 }
60
61 // Create bean instance.
62 if (mbd.isSingleton()) { 63 sharedInstance = getSingleton(beanName, new ObjectFactory() { 64 public Object getObject() throws BeansException { 65 try { 66 return createBean(beanName, mbd, args); 67 }
68 catch (BeansException ex) { 69 // Explicitly remove instance from singleton cache: It might have been put there 70 // eagerly by the creation process, to allow for circular reference resolution. 71 // Also remove any beans that received a temporary reference to the bean.
72 destroySingleton(beanName);
73 throw ex; 74 }
75 }
76 });
77 bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd); 78 }
79
80 else if (mbd.isPrototype()) { 81 // It's a prototype -> create a new instance.
82 Object prototypeInstance = null;
83 try { 84 beforePrototypeCreation(beanName);
85 prototypeInstance = createBean(beanName, mbd, args); 86 }
87 finally { 88 afterPrototypeCreation(beanName);
89 }
90 bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd); 91 }
92
93 else { 94 String scopeName = mbd.getScope(); 95 final Scope scope = this.scopes.get(scopeName);
96 if (scope == null) {
97 throw new IllegalStateException("No Scope registered for scope '" + scopeName + "'");
98 }
99 try { 100 Object scopedInstance = scope.get(beanName, new ObjectFactory() { 101 public Object getObject() throws BeansException { 102 beforePrototypeCreation(beanName); 103 try { 104 return createBean(beanName, mbd, args); 105 } 106 finally { 107 afterPrototypeCreation(beanName); 108 } 109 } 110 }); 111 bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd); 112 } 113 catch (IllegalStateException ex) { 114 throw new BeanCreationException(beanName, 115 "Scope '" + scopeName + "' is not active for the current thread; " +
116 "consider defining a scoped proxy for this bean if you intend to refer to it from a singleton", 117 ex); 118 } 119 } 120 } 121
122 // Check if required type matches the type of the actual bean instance.
123 if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) { 124 try { 125 return getTypeConverter().convertIfNecessary(bean, requiredType); 126 } 127 catch (TypeMismatchException ex) { 128 if (logger.isDebugEnabled()) { 129 logger.debug("Failed to convert bean '" + name + "' to required type [" +
130 ClassUtils.getQualifiedName(requiredType) + "]", ex); 131 } 132 throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass()); 133 } 134 } 135 return (T) bean; 136 }</pre>

首先第9行~第21行的代码，第9行的代码就不进去看了，简单说一下：首先检查一下本地的单例缓存是否已经加载过Bean，没有的话再检查earlySingleton缓存是否已经加载过Bean（又是early，不好找到词语翻译），没有的话执行后面的逻辑。

接着第26行~第50行，这里执行的都是一些基本的检查和简单的操作，包括bean是否是prototype的（prototype的Bean当前创建会抛出异常）、是否抽象的、将beanName加入alreadyCreated这个Set中等。

接着第53行~第59行，我们经常在bean标签中看到depends-on这个属性，就是通过这段保证了depends-on依赖的Bean会优先于当前Bean被加载。

接着第62行~第78行、第80行~第91行、第93行~第120行有三个判断，显然上面的MultiFunctionBean是一个单例的Bean也是本文探究的重点，因此执行第62行~第78行的逻辑。getSingleton方法不贴了，有一些前置的判断，很简单的逻辑，重点就是调用了ObjectFactory的getObject()方法来获取到单例Bean对象，方法的实现是调用了createBean方法，createBean方法是AbstractBeanFactory的子类AbstractAutowireCapableBeanFactory的一个方法，看一下它的方法实现：

<pre> 1 protected Object createBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) 2 throws BeanCreationException { 3
4 if (logger.isDebugEnabled()) { 5 logger.debug("Creating instance of bean '" + beanName + "'");
6 }
7 // Make sure bean class is actually resolved at this point.
8 resolveBeanClass(mbd, beanName);
9
10 // Prepare method overrides.
11 try { 12 mbd.prepareMethodOverrides(); 13 } 14 catch (BeanDefinitionValidationException ex) { 15 throw new BeanDefinitionStoreException(mbd.getResourceDescription(), 16 beanName, "Validation of method overrides failed", ex); 17 } 18
19 try { 20 // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
21 Object bean = resolveBeforeInstantiation(beanName, mbd); 22 if (bean != null) { 23 return bean; 24 } 25 } 26 catch (Throwable ex) { 27 throw new BeanCreationException(mbd.getResourceDescription(), beanName, 28 "BeanPostProcessor before instantiation of bean failed", ex); 29 } 30
31 Object beanInstance = doCreateBean(beanName, mbd, args); 32 if (logger.isDebugEnabled()) { 33 logger.debug("Finished creating instance of bean '" + beanName + "'"); 34 } 35 return beanInstance; 36 }</pre>

前面的代码都没什么意义，代码执行到第31行：

<pre> 1 protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) { 2 // Instantiate the bean.
3 BeanWrapper instanceWrapper = null;
4 if (mbd.isSingleton()) { 5 instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
6 }
7 if (instanceWrapper == null) {
8 instanceWrapper = createBeanInstance(beanName, mbd, args); 9 } 10 final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null); 11 Class beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null); 12
13 // Allow post-processors to modify the merged bean definition.
14 synchronized (mbd.postProcessingLock) { 15 if (!mbd.postProcessed) { 16 applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName); 17 mbd.postProcessed = true; 18 } 19 } 20
21 // Eagerly cache singletons to be able to resolve circular references 22 // even when triggered by lifecycle interfaces like BeanFactoryAware.
23 boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
24 isSingletonCurrentlyInCreation(beanName)); 25 if (earlySingletonExposure) { 26 if (logger.isDebugEnabled()) { 27 logger.debug("Eagerly caching bean '" + beanName +
28 "' to allow for resolving potential circular references"); 29 } 30 addSingletonFactory(beanName, new ObjectFactory() { 31 public Object getObject() throws BeansException { 32 return getEarlyBeanReference(beanName, mbd, bean); 33 } 34 }); 35 } 36
37 // Initialize the bean instance.
38 Object exposedObject = bean; 39 try { 40 populateBean(beanName, mbd, instanceWrapper); 41 if (exposedObject != null) { 42 exposedObject = initializeBean(beanName, exposedObject, mbd); 43 } 44 } 45 catch (Throwable ex) { 46 if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) { 47 throw (BeanCreationException) ex; 48 } 49 else { 50 throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex); 51 } 52 } 53
54 if (earlySingletonExposure) { 55 Object earlySingletonReference = getSingleton(beanName, false); 56 if (earlySingletonReference != null) { 57 if (exposedObject == bean) { 58 exposedObject = earlySingletonReference; 59 } 60 else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) { 61 String[] dependentBeans = getDependentBeans(beanName); 62 Set<String> actualDependentBeans = new LinkedHashSet<String>(dependentBeans.length); 63 for (String dependentBean : dependentBeans) { 64 if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) { 65 actualDependentBeans.add(dependentBean); 66 } 67 } 68 if (!actualDependentBeans.isEmpty()) { 69 throw new BeanCurrentlyInCreationException(beanName, 70 "Bean with name '" + beanName + "' has been injected into other beans [" +
71 StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
72 "] in its raw version as part of a circular reference, but has eventually been " +
73 "wrapped. This means that said other beans do not use the final version of the " +
74 "bean. This is often the result of over-eager type matching - consider using " +
75 "'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example."); 76 } 77 } 78 } 79 } 80
81 // Register bean as disposable.
82 try { 83 registerDisposableBeanIfNecessary(beanName, bean, mbd); 84 } 85 catch (BeanDefinitionValidationException ex) { 86 throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex); 87 } 88
89 return exposedObject; 90 }</pre>

doCreateBean方法

代码跟踪到这里，已经到了主流程，接下来分段分析doCreateBean方法的代码。

创建Bean实例

第8行的createBeanInstance方法，会创建出Bean的实例，并包装为BeanWrapper，看一下createBeanInstance方法，只贴最后一段比较关键的：

<pre> 1 // Need to determine the constructor...
2 Constructor[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName); 3 if (ctors != null ||
4 mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR ||
5 mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
6 return autowireConstructor(beanName, mbd, ctors, args); 7 }
8
9 // No special handling: simply use no-arg constructor.
10 return instantiateBean(beanName, mbd);</pre>

意思是bean标签使用构造函数注入属性的话，执行第6行，否则执行第10行。MultiFunctionBean使用默认构造函数，使用setter注入属性，因此执行第10行代码：

<pre> 1 protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) { 2 try { 3 Object beanInstance;
4 final BeanFactory parent = this;
5 if (System.getSecurityManager() != null) {
6 beanInstance = AccessController.doPrivileged(new PrivilegedAction<Object>() {
7 public Object run() { 8 return getInstantiationStrategy().instantiate(mbd, beanName, parent); 9 } 10 }, getAccessControlContext()); 11 } 12 else { 13 beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent); 14 } 15 BeanWrapper bw = new BeanWrapperImpl(beanInstance); 16 initBeanWrapper(bw); 17 return bw; 18 } 19 catch (Throwable ex) { 20 throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex); 21 } 22 }</pre>

代码执行到13行：

<pre> 1 public Object instantiate(RootBeanDefinition beanDefinition, String beanName, BeanFactory owner) { 2 // Don't override the class with CGLIB if no overrides.
3 if (beanDefinition.getMethodOverrides().isEmpty()) { 4 Constructor<?> constructorToUse; 5 synchronized (beanDefinition.constructorArgumentLock) { 6 constructorToUse = (Constructor<?>) beanDefinition.resolvedConstructorOrFactoryMethod;
7 if (constructorToUse == null) {
8 final Class clazz = beanDefinition.getBeanClass(); 9 if (clazz.isInterface()) { 10 throw new BeanInstantiationException(clazz, "Specified class is an interface"); 11 } 12 try { 13 if (System.getSecurityManager() != null) { 14 constructorToUse = AccessController.doPrivileged(new PrivilegedExceptionAction<Constructor>() { 15 public Constructor run() throws Exception { 16 return clazz.getDeclaredConstructor((Class[]) null); 17 } 18 }); 19 } 20 else { 21 constructorToUse = clazz.getDeclaredConstructor((Class[]) null); 22 } 23 beanDefinition.resolvedConstructorOrFactoryMethod = constructorToUse; 24 } 25 catch (Exception ex) { 26 throw new BeanInstantiationException(clazz, "No default constructor found", ex); 27 } 28 } 29 } 30 return BeanUtils.instantiateClass(constructorToUse); 31 } 32 else { 33 // Must generate CGLIB subclass.
34 return instantiateWithMethodInjection(beanDefinition, beanName, owner); 35 } 36 }</pre>

整段代码都在做一件事情，就是选择一个使用的构造函数。当然第9行顺带做了一个判断：实例化一个接口将报错。

最后调用到30行，看一下代码：

<pre> 1 public static <T> T instantiateClass(Constructor<T> ctor, Object... args) throws BeanInstantiationException { 2 Assert.notNull(ctor, "Constructor must not be null");
3 try { 4 ReflectionUtils.makeAccessible(ctor);
5 return ctor.newInstance(args); 6 }
7 catch (InstantiationException ex) { 8 throw new BeanInstantiationException(ctor.getDeclaringClass(), 9 "Is it an abstract class?", ex); 10 } 11 catch (IllegalAccessException ex) { 12 throw new BeanInstantiationException(ctor.getDeclaringClass(), 13 "Is the constructor accessible?", ex); 14 } 15 catch (IllegalArgumentException ex) { 16 throw new BeanInstantiationException(ctor.getDeclaringClass(), 17 "Illegal arguments for constructor", ex); 18 } 19 catch (InvocationTargetException ex) { 20 throw new BeanInstantiationException(ctor.getDeclaringClass(), 21 "Constructor threw exception", ex.getTargetException()); 22 } 23 }</pre>

通过反射生成Bean的实例。看到前面有一步makeAccessible，这意味着即使Bean的构造函数是private、protected的，依然不影响Bean的构造。

最后注意一下，这里被实例化出来的Bean并不会直接返回，而是会被包装为BeanWrapper继续在后面使用。

doCreateBean方法

上文【Spring源码分析】非懒加载的单例Bean初始化过程（上篇），分析了单例的Bean初始化流程，并跟踪代码进入了主流程，看到了Bean是如何被实例化出来的。先贴一下AbstractAutowireCapableBeanFactory的doCreateBean方法代码：

<pre> 1 protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) { 2 // Instantiate the bean.
3 BeanWrapper instanceWrapper = null;
4 if (mbd.isSingleton()) { 5 instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
6 }
7 if (instanceWrapper == null) {
8 instanceWrapper = createBeanInstance(beanName, mbd, args); 9 } 10 final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null); 11 Class beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null); 12
13 // Allow post-processors to modify the merged bean definition.
14 synchronized (mbd.postProcessingLock) { 15 if (!mbd.postProcessed) { 16 applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName); 17 mbd.postProcessed = true; 18 } 19 } 20
21 // Eagerly cache singletons to be able to resolve circular references 22 // even when triggered by lifecycle interfaces like BeanFactoryAware.
23 boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
24 isSingletonCurrentlyInCreation(beanName)); 25 if (earlySingletonExposure) { 26 if (logger.isDebugEnabled()) { 27 logger.debug("Eagerly caching bean '" + beanName +
28 "' to allow for resolving potential circular references"); 29 } 30 addSingletonFactory(beanName, new ObjectFactory() { 31 public Object getObject() throws BeansException { 32 return getEarlyBeanReference(beanName, mbd, bean); 33 } 34 }); 35 } 36
37 // Initialize the bean instance.
38 Object exposedObject = bean; 39 try { 40 populateBean(beanName, mbd, instanceWrapper); 41 if (exposedObject != null) { 42 exposedObject = initializeBean(beanName, exposedObject, mbd); 43 } 44 } 45 catch (Throwable ex) { 46 if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) { 47 throw (BeanCreationException) ex; 48 } 49 else { 50 throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex); 51 } 52 } 53
54 if (earlySingletonExposure) { 55 Object earlySingletonReference = getSingleton(beanName, false); 56 if (earlySingletonReference != null) { 57 if (exposedObject == bean) { 58 exposedObject = earlySingletonReference; 59 } 60 else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) { 61 String[] dependentBeans = getDependentBeans(beanName); 62 Set<String> actualDependentBeans = new LinkedHashSet<String>(dependentBeans.length); 63 for (String dependentBean : dependentBeans) { 64 if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) { 65 actualDependentBeans.add(dependentBean); 66 } 67 } 68 if (!actualDependentBeans.isEmpty()) { 69 throw new BeanCurrentlyInCreationException(beanName, 70 "Bean with name '" + beanName + "' has been injected into other beans [" +
71 StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
72 "] in its raw version as part of a circular reference, but has eventually been " +
73 "wrapped. This means that said other beans do not use the final version of the " +
74 "bean. This is often the result of over-eager type matching - consider using " +
75 "'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example."); 76 } 77 } 78 } 79 } 80
81 // Register bean as disposable.
82 try { 83 registerDisposableBeanIfNecessary(beanName, bean, mbd); 84 } 85 catch (BeanDefinitionValidationException ex) { 86 throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex); 87 } 88
89 return exposedObject; 90 }</pre>

下面继续分析初始化一个Bean的流程，不太重要的流程就跳过了。

属性注入

属性注入的代码比较好找，可以看一下40行，取名为populateBean，即填充Bean的意思，看一下代码实现：

<pre> 1 protected void populateBean(String beanName, AbstractBeanDefinition mbd, BeanWrapper bw) { 2 PropertyValues pvs = mbd.getPropertyValues(); 3
4 if (bw == null) {
5 if (!pvs.isEmpty()) {
6 throw new BeanCreationException( 7 mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
8 }
9 else { 10 // Skip property population phase for null instance.
11 return; 12 } 13 } 14
15 // Give any InstantiationAwareBeanPostProcessors the opportunity to modify the 16 // state of the bean before properties are set. This can be used, for example, 17 // to support styles of field injection.
18 boolean continueWithPropertyPopulation = true; 19
20 if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) { 21 for (BeanPostProcessor bp : getBeanPostProcessors()) { 22 if (bp instanceof InstantiationAwareBeanPostProcessor) { 23 InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; 24 if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) { 25 continueWithPropertyPopulation = false; 26 break; 27 } 28 } 29 } 30 } 31
32 if (!continueWithPropertyPopulation) { 33 return; 34 } 35
36 if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
37 mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) { 38 MutablePropertyValues newPvs = new MutablePropertyValues(pvs); 39
40 // Add property values based on autowire by name if applicable.
41 if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) { 42 autowireByName(beanName, mbd, bw, newPvs); 43 } 44
45 // Add property values based on autowire by type if applicable.
46 if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) { 47 autowireByType(beanName, mbd, bw, newPvs); 48 } 49
50 pvs = newPvs; 51 } 52
53 boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors(); 54 boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE); 55
56 if (hasInstAwareBpps || needsDepCheck) { 57 PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw); 58 if (hasInstAwareBpps) { 59 for (BeanPostProcessor bp : getBeanPostProcessors()) { 60 if (bp instanceof InstantiationAwareBeanPostProcessor) { 61 InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; 62 pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName); 63 if (pvs == null) { 64 return; 65 } 66 } 67 } 68 } 69 if (needsDepCheck) { 70 checkDependencies(beanName, mbd, filteredPds, pvs); 71 } 72 } 73
74 applyPropertyValues(beanName, mbd, bw, pvs); 75 }</pre>

这段代码层次有点深，跟一下74行的applyPropertyValues方法，最后那个pvs的实现类为MutablePropertyValues，里面持有一个List<PropertyValue>，每一个PropertyValue包含了此Bean属性的属性名与属性值。74行的代码实现为：

<pre> 1 protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) { 2 if (pvs == null || pvs.isEmpty()) { 3 return;
4 }
5
6 MutablePropertyValues mpvs = null;
7 List<PropertyValue> original; 8
9 if (System.getSecurityManager()!= null) { 10 if (bw instanceof BeanWrapperImpl) { 11 ((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext()); 12 } 13 } 14
15 if (pvs instanceof MutablePropertyValues) { 16 mpvs = (MutablePropertyValues) pvs; 17 if (mpvs.isConverted()) { 18 // Shortcut: use the pre-converted values as-is.
19 try { 20 bw.setPropertyValues(mpvs); 21 return; 22 } 23 catch (BeansException ex) { 24 throw new BeanCreationException( 25 mbd.getResourceDescription(), beanName, "Error setting property values", ex); 26 } 27 } 28 original = mpvs.getPropertyValueList(); 29 } 30 else { 31 original = Arrays.asList(pvs.getPropertyValues()); 32 } 33
34 TypeConverter converter = getCustomTypeConverter(); 35 if (converter == null) { 36 converter = bw; 37 } 38 BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter); 39
40 // Create a deep copy, resolving any references for values.
41 List<PropertyValue> deepCopy = new ArrayList<PropertyValue>(original.size()); 42 boolean resolveNecessary = false; 43 for (PropertyValue pv : original) { 44 if (pv.isConverted()) { 45 deepCopy.add(pv); 46 } 47 else { 48 String propertyName = pv.getName(); 49 Object originalValue = pv.getValue(); 50 Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue); 51 Object convertedValue = resolvedValue; 52 boolean convertible = bw.isWritableProperty(propertyName) &&
53 !PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName); 54 if (convertible) { 55 convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter); 56 } 57 // Possibly store converted value in merged bean definition, 58 // in order to avoid re-conversion for every created bean instance.
59 if (resolvedValue == originalValue) { 60 if (convertible) { 61 pv.setConvertedValue(convertedValue); 62 } 63 deepCopy.add(pv); 64 } 65 else if (convertible && originalValue instanceof TypedStringValue &&
66 !((TypedStringValue) originalValue).isDynamic() &&
67 !(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) { 68 pv.setConvertedValue(convertedValue); 69 deepCopy.add(pv); 70 } 71 else { 72 resolveNecessary = true; 73 deepCopy.add(new PropertyValue(pv, convertedValue)); 74 } 75 } 76 } 77 if (mpvs != null && !resolveNecessary) { 78 mpvs.setConverted(); 79 } 80
81 // Set our (possibly massaged) deep copy.
82 try { 83 bw.setPropertyValues(new MutablePropertyValues(deepCopy)); 84 } 85 catch (BeansException ex) { 86 throw new BeanCreationException( 87 mbd.getResourceDescription(), beanName, "Error setting property values", ex); 88 } 89 }</pre>

之后在第41行~第76行做了一次深拷贝（只是名字叫做深拷贝而已，其实就是遍历PropertyValue然后一个一个赋值到一个新的List而不是Java语义上的Clone，这里使用深拷贝是为了解析Values值中的所有引用），将PropertyValue一个一个赋值到一个新的List里面去，起名为deepCopy。最后执行83行进行复制，bw即BeanWrapper，持有Bean实例的一个Bean包装类，看一下代码实现：

<pre> 1 public void setPropertyValues(PropertyValues pvs, boolean ignoreUnknown, boolean ignoreInvalid) 2 throws BeansException { 3
4 List<PropertyAccessException> propertyAccessExceptions = null;
5 List<PropertyValue> propertyValues = (pvs instanceof MutablePropertyValues ?
6 ((MutablePropertyValues) pvs).getPropertyValueList() : Arrays.asList(pvs.getPropertyValues()));
7 for (PropertyValue pv : propertyValues) { 8 try { 9 // This method may throw any BeansException, which won't be caught 10 // here, if there is a critical failure such as no matching field. 11 // We can attempt to deal only with less serious exceptions.
12 setPropertyValue(pv); 13 } 14 catch (NotWritablePropertyException ex) { 15 if (!ignoreUnknown) { 16 throw ex; 17 } 18 // Otherwise, just ignore it and continue...
19 } 20 catch (NullValueInNestedPathException ex) { 21 if (!ignoreInvalid) { 22 throw ex; 23 } 24 // Otherwise, just ignore it and continue...
25 } 26 catch (PropertyAccessException ex) { 27 if (propertyAccessExceptions == null) { 28 propertyAccessExceptions = new LinkedList<PropertyAccessException>(); 29 } 30 propertyAccessExceptions.add(ex); 31 } 32 } 33
34 // If we encountered individual exceptions, throw the composite exception.
35 if (propertyAccessExceptions != null) { 36 PropertyAccessException[] paeArray =
37 propertyAccessExceptions.toArray(new PropertyAccessException[propertyAccessExceptions.size()]); 38 throw new PropertyBatchUpdateException(paeArray); 39 } 40 }</pre>

这段代码没什么特别的，遍历前面的deepCopy，拿每一个PropertyValue，执行第12行的setPropertyValue：

<pre> 1 public void setPropertyValue(PropertyValue pv) throws BeansException { 2 PropertyTokenHolder tokens = (PropertyTokenHolder) pv.resolvedTokens; 3 if (tokens == null) {
4 String propertyName = pv.getName(); 5 BeanWrapperImpl nestedBw;
6 try { 7 nestedBw = getBeanWrapperForPropertyPath(propertyName); 8 }
9 catch (NotReadablePropertyException ex) { 10 throw new NotWritablePropertyException(getRootClass(), this.nestedPath + propertyName, 11 "Nested property in path '" + propertyName + "' does not exist", ex); 12 } 13 tokens = getPropertyNameTokens(getFinalPath(nestedBw, propertyName)); 14 if (nestedBw == this) { 15 pv.getOriginalPropertyValue().resolvedTokens = tokens; 16 } 17 nestedBw.setPropertyValue(tokens, pv); 18 } 19 else { 20 setPropertyValue(tokens, pv); 21 } 22 }</pre>

找一个合适的BeanWrapper，这里就是自身，然后执行17行的setPropertyValue方法进入最后一步，方法非常长，截取核心的一段：

<pre> 1 final Method writeMethod = (pd instanceof GenericTypeAwarePropertyDescriptor ?
2 ((GenericTypeAwarePropertyDescriptor) pd).getWriteMethodForActualAccess() :
3 pd.getWriteMethod());
4 if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers()) && !writeMethod.isAccessible()) {
5 if (System.getSecurityManager()!= null) {
6 AccessController.doPrivileged(new PrivilegedAction<Object>() {
7 public Object run() { 8 writeMethod.setAccessible(true);
9 return null; 10 } 11 }); 12 } 13 else { 14 writeMethod.setAccessible(true); 15 } 16 } 17 final Object value = valueToApply; 18 if (System.getSecurityManager() != null) { 19 try { 20 AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() { 21 public Object run() throws Exception { 22 writeMethod.invoke(object, value); 23 return null; 24 } 25 }, acc); 26 } 27 catch (PrivilegedActionException ex) { 28 throw ex.getException(); 29 } 30 } 31 else { 32 writeMethod.invoke(this.object, value); 33 } </pre>

大致流程就是两步：

（1）拿到写方法并将方法的可见性设置为true

（2）拿到Value值，对Bean通过反射调用写方法

这样完成了对于Bean属性值的设置。

Aware注入

接下来是Aware注入。在使用Spring的时候我们将自己的Bean实现BeanNameAware接口、BeanFactoryAware接口等，依赖容器帮我们注入当前Bean的名称或者Bean工厂，其代码实现先追溯到上面doCreateBean方法的42行initializeBean方法：

<pre> 1 protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) { 2 if (System.getSecurityManager() != null) {
3 AccessController.doPrivileged(new PrivilegedAction<Object>() {
4 public Object run() { 5 invokeAwareMethods(beanName, bean);
6 return null;
7 }
8 }, getAccessControlContext());
9 } 10 else { 11 invokeAwareMethods(beanName, bean); 12 } 13
14 Object wrappedBean = bean; 15 if (mbd == null || !mbd.isSynthetic()) { 16 wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName); 17 } 18
19 try { 20 invokeInitMethods(beanName, wrappedBean, mbd); 21 } 22 catch (Throwable ex) { 23 throw new BeanCreationException( 24 (mbd != null ? mbd.getResourceDescription() : null), 25 beanName, "Invocation of init method failed", ex); 26 } 27
28 if (mbd == null || !mbd.isSynthetic()) { 29 wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName); 30 } 31 return wrappedBean; 32 }</pre>

看一下上面第5行的实现：

<pre> 1 private void invokeAwareMethods(final String beanName, final Object bean) { 2 if (bean instanceof BeanNameAware) { 3 ((BeanNameAware) bean).setBeanName(beanName);
4 }
5 if (bean instanceof BeanClassLoaderAware) { 6 ((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());
7 }
8 if (bean instanceof BeanFactoryAware) { 9 ((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this); 10 } 11 }</pre>

看到这里判断，如果bean是BeanNameAware接口的实现类会调用setBeanName方法、如果bean是BeanClassLoaderAware接口的实现类会调用setBeanClassLoader方法、如果是BeanFactoryAware接口的实现类会调用setBeanFactory方法，注入对应的属性值。

调用BeanPostProcessor的postProcessBeforeInitialization方法

上面initializeBean方法再看16行其实现：

<pre> 1 public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName) 2 throws BeansException { 3
4 Object result = existingBean; 5 for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) { 6 result = beanProcessor.postProcessBeforeInitialization(result, beanName); 7 if (result == null) {
8 return result; 9 } 10 } 11 return result; 12 }</pre>

遍历每个BeanPostProcessor接口实现，调用postProcessBeforeInitialization方法，这个接口的调用时机之后会总结，这里就代码先简单提一下。

调用初始化方法

initializeBean方法的20行，调用Bean的初始化方法，看一下实现：

<pre> 1 protected void invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd) 2 throws Throwable { 3
4 boolean isInitializingBean = (bean instanceof InitializingBean); 5 if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
6 if (logger.isDebugEnabled()) { 7 logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
8 }
9 if (System.getSecurityManager() != null) { 10 try { 11 AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() { 12 public Object run() throws Exception { 13 ((InitializingBean) bean).afterPropertiesSet(); 14 return null; 15 } 16 }, getAccessControlContext()); 17 } 18 catch (PrivilegedActionException pae) { 19 throw pae.getException(); 20 } 21 } 22 else { 23 ((InitializingBean) bean).afterPropertiesSet(); 24 } 25 } 26
27 if (mbd != null) { 28 String initMethodName = mbd.getInitMethodName(); 29 if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
30 !mbd.isExternallyManagedInitMethod(initMethodName)) { 31 invokeCustomInitMethod(beanName, bean, mbd); 32 } 33 } 34 }</pre>

看到，代码做了两件事情：

1、先判断Bean是否InitializingBean的实现类，是的话，将Bean强转为InitializingBean，直接调用afterPropertiesSet()方法

2、尝试去拿init-method，假如有的话，通过反射，调用initMethod

因此，两种方法各有优劣：使用实现InitializingBean接口的方式效率更高一点，因为init-method方法是通过反射进行调用的；从另外一个角度讲，使用init-method方法之后和Spring的耦合度会更低一点。具体使用哪种方式调用初始化方法，看个人喜好。

调用BeanPostProcessor的postProcessAfterInitialization方法

最后一步，initializeBean方法的29行：

<pre> 1 public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName) 2 throws BeansException { 3
4 Object result = existingBean; 5 for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) { 6 result = beanProcessor.postProcessAfterInitialization(result, beanName); 7 if (result == null) {
8 return result; 9 } 10 } 11 return result; 12 }</pre>

同样遍历BeanPostProcessor，调用postProcessAfterInitialization方法。因此对于BeanPostProcessor方法总结一下：

1、在初始化每一个Bean的时候都会调用每一个配置的BeanPostProcessor的方法

2、在Bean属性设置、Aware设置后调用postProcessBeforeInitialization方法

3、在初始化方法调用后调用postProcessAfterInitialization方法

注册需要执行销毁方法的Bean

接下来看一下最上面doCreateBean方法的第83行registerDisposableBeanIfNecessary(beanName, bean, mbd)这一句，完成了创建Bean的最后一件事情：注册需要执行销毁方法的Bean。

看一下方法的实现：

<pre> 1 protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd) { 2 AccessControlContext acc = (System.getSecurityManager() != null ? getAccessControlContext() : null);
3 if (!mbd.isPrototype() && requiresDestruction(bean, mbd)) { 4 if (mbd.isSingleton()) { 5 // Register a DisposableBean implementation that performs all destruction 6 // work for the given bean: DestructionAwareBeanPostProcessors, 7 // DisposableBean interface, custom destroy method.
8 registerDisposableBean(beanName,
9 new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc)); 10 } 11 else { 12 // A bean with a custom scope...
13 Scope scope = this.scopes.get(mbd.getScope()); 14 if (scope == null) { 15 throw new IllegalStateException("No Scope registered for scope '" + mbd.getScope() + "'"); 16 } 17 scope.registerDestructionCallback(beanName, 18 new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc)); 19 } 20 } 21 }</pre>

其中第3行第一个判断为必须不是prototype（原型）的，第二个判断requiresDestruction方法的实现为：

<pre>1 protected boolean requiresDestruction(Object bean, RootBeanDefinition mbd) { 2 return (bean != null &&
3 (bean instanceof DisposableBean || mbd.getDestroyMethodName() != null ||
4 hasDestructionAwareBeanPostProcessors())); 5 }</pre>

要注册销毁方法，Bean需要至少满足以下三个条件之一：

（1）Bean是DisposableBean的实现类，此时执行DisposableBean的接口方法destroy()

（2）Bean标签中有配置destroy-method属性，此时执行destroy-method配置指定的方法

（3）当前Bean对应的BeanFactory中持有DestructionAwareBeanPostProcessor接口的实现类，此时执行DestructionAwareBeanPostProcessor的接口方法postProcessBeforeDestruction

在满足上面三个条件之一的情况下，容器便会注册销毁该Bean，注册Bean的方法很简单，见registerDisposableBean方法实现：

<pre>1 public void registerDisposableBean(String beanName, DisposableBean bean) { 2 synchronized (this.disposableBeans) { 3 this.disposableBeans.put(beanName, bean); 4 } 5 }</pre>

容器销毁的时候，会遍历disposableBeans，逐一执行销毁方法。

流程总结

本文和上篇文章分析了Spring Bean初始化的步骤，最后用一幅图总结一下Spring Bean初始化的流程：

图只是起梳理流程作用，抛砖引玉，具体代码实现还需要网友朋友们照着代码自己去一步一步分析。

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