1 protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
 2             @Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
 3 
 4     /**
 5      * 通过name获取beanName,这里不使用name直接作为beanName有两个原因：
 6      *  1.name可能是以&开头的，表明调用者想获取FactoryBean本身，而非FactoryBean;在beanFactory中factoryBean的存储也是map格式
 7      *    <beanName,bean> 只是说，普通的beanName是没有&这个字符串的，所以，需要将name的首字母移除，这样才能从缓存中拿到factoryBean
 8      *  2.还是别名的问题，需要转换
 9      */
10     final String beanName = transformedBeanName(name);
11     Object bean;
12 
13     /**
14      * 1.从单例池中获取当前bean
15      * 2.这里是循环依赖的重要方法之一
16      *
17      */
18     // Eagerly check singleton cache for manually registered singletons.
19     Object sharedInstance = getSingleton(beanName);
20     if (sharedInstance != null && args == null) {
21         if (logger.isDebugEnabled()) {
22             if (isSingletonCurrentlyInCreation(beanName)) {
23                 logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
24                         "' that is not fully initialized yet - a consequence of a circular reference");
25             }
26             else {
27                 logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
28             }
29         }
30         bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
31     }
32 
33     else {
34         // Fail if we're already creating this bean instance:
35         // We're assumably within a circular reference.
36         /**
37          * 这里判断bean是否在创建过程中，是第二次调用的时候 才会判断；如果是第一次执行到这里，set集合是空（这里判断的是原型bean）
38          */
39         if (isPrototypeCurrentlyInCreation(beanName)) {
40             throw new BeanCurrentlyInCreationException(beanName);
41         }
42 
43         //添加到alreadyCreated集合当中，表示当前bean已经创建过一次了
44         if (!typeCheckOnly) {
45             markBeanAsCreated(beanName);
46         }
47 
48         try {
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 dep : dependsOn) {
56                     if (isDependent(beanName, dep)) {
57                         throw new BeanCreationException(mbd.getResourceDescription(), beanName,
58                                 "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
59                     }
60                     registerDependentBean(dep, beanName);
61                     try {
62                         getBean(dep);
63                     }
64                     catch (NoSuchBeanDefinitionException ex) {
65                         throw new BeanCreationException(mbd.getResourceDescription(), beanName,
66                                 "'" + beanName + "' depends on missing bean '" + dep + "'", ex);
67                     }
68                 }
69             }
70 
71             // Create bean instance.如果当前bean是单实例的，就调用createBean
72             if (mbd.isSingleton()) {
73                 sharedInstance = getSingleton(beanName, () -> {
74                     try {
75                         return createBean(beanName, mbd, args);
76                     }
77                     catch (BeansException ex) {
78                         // Explicitly remove instance from singleton cache: It might have been put there
79                         // eagerly by the creation process, to allow for circular reference resolution.
80                         // Also remove any beans that received a temporary reference to the bean.
81                         destroySingleton(beanName);
82                         throw ex;
83                     }
84                 });
85                 bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
86             }
87         }
88         catch (BeansException ex) {
89             cleanupAfterBeanCreationFailure(beanName);
90             throw ex;
91         }
92     }
93 
94 
95     return (T) bean;
96 }

 1 protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
 2             throws BeanCreationException {
 3 
 4     // Instantiate the bean.
 5     BeanWrapper instanceWrapper = null;
 6     if (mbd.isSingleton()) {
 7         instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
 8     }
 9     if (instanceWrapper == null) {
10         /**
11          *  创建bean实例，并将bean实例包裹在BeanWrapper实现类对象中返回，
12          *  createBeanInstance中包含三种创建bean的方式
13          *    1.通过工厂方法创建bean实例
14          *    2.通过构造方法自动注入的方式创建bean实例
15          *    3.通过无参构造方法创建bean实例
16          *
17          *  如果bean的配置中配置了lookup-method和replace-method  则会使用增强bean实例
18          *
19          * 在这个方法中完成了对bean的创建(仅仅是new出来，也就是说在这个方法里面推断要使用哪个构造函数来创建bean对象)
20          * 然后完成bean的初始化
21          *
22          */
23         instanceWrapper = createBeanInstance(beanName, mbd, args);
24     }
25     final Object bean = instanceWrapper.getWrappedInstance();
26     Class<?> beanType = instanceWrapper.getWrappedClass();
27     if (beanType != NullBean.class) {
28         mbd.resolvedTargetType = beanType;
29     }
30 
31     // Allow post-processors to modify the merged bean definition.
32     synchronized (mbd.postProcessingLock) {
33         if (!mbd.postProcessed) {
34             try {
35                 //mpy 第三次调用后置处理器  缓存注解信息
36                 applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
37             }
38             catch (Throwable ex) {
39                 throw new BeanCreationException(mbd.getResourceDescription(), beanName,
40                         "Post-processing of merged bean definition failed", ex);
41             }
42             mbd.postProcessed = true;
43         }
44     }
45 
46     // Eagerly cache singletons to be able to resolve circular references
47     // even when triggered by lifecycle interfaces like BeanFactoryAware.
48     boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
49             isSingletonCurrentlyInCreation(beanName));
50     if (earlySingletonExposure) {
51         if (logger.isDebugEnabled()) {
52             logger.debug("Eagerly caching bean '" + beanName +
53                     "' to allow for resolving potential circular references");
54         }
55         //mpy 第四次调用后置处理器 获取一个提前暴露的对象  用来解决循环依赖
56         addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
57     }
58 
59     // Initialize the bean instance.
60     Object exposedObject = bean;
61     try {
62         //在populateBean(beanName, mbd, instanceWrapper);方法中完成第五次第六次调用后置处理器
63         populateBean(beanName, mbd, instanceWrapper);
64         //在initialzeBean中完成第七次第八次后置处理器调用
65         exposedObject = initializeBean(beanName, exposedObject, mbd);
66     }
67     catch (Throwable ex) {
68         if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
69             throw (BeanCreationException) ex;
70         }
71         else {
72             throw new BeanCreationException(
73                     mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
74         }
75     }
76     return exposedObject;
77 }