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转自：http://www.cnblogs.com/xrq730
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：
1 ApplicationContext ac = new ClassPathXmlApplicationContext("spring.xml");
2 ac.getBean(XXX.class);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：
1 public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
2 this(new String[] {configLocation}, true, null);
3 }
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 }
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
3、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：
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 }
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：
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 }
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：
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 }
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：
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 }
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源码分析】非懒加载的单例Bean初始化过程（上篇）
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：
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 }
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：
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 }
定义对应的spring.xml：
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.org/schema/beans/spring-beans-3.0.xsd">
6
7 <bean id="multiFunctionBean" class="org.xrq.action.MultiFunctionBean" init-method="initMethod" />
8
9 </beans>
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。
看一下doGetBean方法的代码实现，比较长：
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 }
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：
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 }
前面的代码都没什么意义，代码执行到第31行：
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 }
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：
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);
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：
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 }
代码执行到13行：
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 }
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：
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 }
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：
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 }
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：
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 }
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：
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 }
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：
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 }
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：
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 }
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：
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 }
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：
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 }
看一下上面第5行的实现：
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 }
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：
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 }
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：
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 }
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：
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 }
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：
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 }
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：
1 protected boolean requiresDestruction(Object bean, RootBeanDefinition mbd) {
2 return (bean != null &&
3 (bean instanceof DisposableBean || mbd.getDestroyMethodName() != null ||
4 hasDestructionAwareBeanPostProcessors()));
5 }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：
1 public void registerDisposableBean(String beanName, DisposableBean bean) {
2 synchronized (this.disposableBeans) {
3 this.disposableBeans.put(beanName, bean);
4 }
5 }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。
