【spring源码分析】IOC容器初始化（八）

 1 protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
 2             throws BeanCreationException {
 3         if (logger.isDebugEnabled()) {
 4             logger.debug("Creating instance of bean ‘" + beanName + "‘");
 5         }
 6         RootBeanDefinition mbdToUse = mbd;
 7 
 8         // Make sure bean class is actually resolved at this point, and
 9         // clone the bean definition in case of a dynamically resolved Class
10         // which cannot be stored in the shared merged bean definition.
11         // 确保此时的bean已经被解析了
12         // 如果获取的class属性不为null，则克隆该BeanDefinition，主要是因为动态解析的class无法保存到共享的BeanDefinition
13         Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
14         if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
15             mbdToUse = new RootBeanDefinition(mbd);
16             mbdToUse.setBeanClass(resolvedClass);
17         }
18 
19         // Prepare method overrides.
20         try {
21             // 验证和准备覆盖方法
22             mbdToUse.prepareMethodOverrides();
23         } catch (BeanDefinitionValidationException ex) {
24             throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
25                                                    beanName, "Validation of method overrides failed", ex);
26         }
27 
28         try {
29             // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
30             // 实例化的前置处理
31             // 给BeanPostProcessor一个机会用来返回一个代理类而不是真正的实例类
32             // AOP的功能就是基于这个地方
33             Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
34             if (bean != null) {
35                 return bean;
36             }
37         } catch (Throwable ex) {
38             throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
39                                             "BeanPostProcessor before instantiation of bean failed", ex);
40         }
41 
42         try {
43             // 创建Bean对象
44             Object beanInstance = doCreateBean(beanName, mbdToUse, args);
45             if (logger.isDebugEnabled()) {
46                 logger.debug("Finished creating instance of bean ‘" + beanName + "‘");
47             }
48             return beanInstance;
49         } catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
50             // A previously detected exception with proper bean creation context already,
51             // or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
52             throw ex;
53         } catch (Throwable ex) {
54             throw new BeanCreationException(
55                     mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
56         }
57     }

 1 protected Class<?> resolveBeanClass(final RootBeanDefinition mbd, String beanName, final Class<?>... typesToMatch)
 2             throws CannotLoadBeanClassException {
 3 
 4         try {
 5             if (mbd.hasBeanClass()) {
 6                 return mbd.getBeanClass();
 7             }
 8             if (System.getSecurityManager() != null) {
 9                 return AccessController.doPrivileged((PrivilegedExceptionAction<Class<?>>) () ->
10                         doResolveBeanClass(mbd, typesToMatch), getAccessControlContext());
11             } else {
12                 return doResolveBeanClass(mbd, typesToMatch);
13             }
14         // ..... 省略异常处理
15     }

 1 public void prepareMethodOverrides() throws BeanDefinitionValidationException {
 2         // Check that lookup methods exists.
 3         // 如果方法可以覆盖
 4         if (hasMethodOverrides()) {
 5             // 得到覆盖方法
 6             Set<MethodOverride> overrides = getMethodOverrides().getOverrides();
 7             // 同步
 8             synchronized (overrides) {
 9                 // 循环调用 prepareMethodOverride进行覆盖准备
10                 for (MethodOverride mo : overrides) {
11                     prepareMethodOverride(mo);
12                 }
13             }
14         }
15     }

 1 // AbstractBeanDefinition
 2 protected void prepareMethodOverride(MethodOverride mo) throws BeanDefinitionValidationException {
 3         int count = ClassUtils.getMethodCountForName(getBeanClass(), mo.getMethodName());
 4         if (count == 0) {
 5             throw new BeanDefinitionValidationException(
 6                     "Invalid method override: no method with name ‘" + mo.getMethodName() +
 7                             "‘ on class [" + getBeanClassName() + "]");
 8         } else if (count == 1) {
 9             // Mark override as not overloaded, to avoid the overhead of arg type checking.
10             mo.setOverloaded(false);
11         }
12     }

 1 protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
 2         Object bean = null;
 3         // 如果bean不是应用系统的，有BeanPostProcessor
 4         if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
 5             // Make sure bean class is actually resolved at this point.
 6             if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
 7                 Class<?> targetType = determineTargetType(beanName, mbd);
 8                 if (targetType != null) {
 9                     // 前置处理
10                     bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
11                     if (bean != null) {
12                         // 后置处理
13                         bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
14                     }
15                 }
16             }
17             mbd.beforeInstantiationResolved = (bean != null);
18         }
19         return bean;
20     }

  1 protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
  2             throws BeanCreationException {
  3 
  4         // Instantiate the bean.
  5         // BeanWrapper是对Bean的包装，其接口中所定义的功能很简单包括设置获取被包装的对象、获取被包装bean的属性描述器
  6         BeanWrapper instanceWrapper = null;
  7         // 如果是单例模型，则从未完成的FactoryBean缓存中删除
  8         if (mbd.isSingleton()) {
  9             instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
 10         }
 11         // 使用合适的实例化策略来创建新的实例：工厂方法、构造函数自动注入、简单初始化
 12         if (instanceWrapper == null) {
 13             instanceWrapper = createBeanInstance(beanName, mbd, args);
 14         }
 15         // 包装的对象实例
 16         final Object bean = instanceWrapper.getWrappedInstance();
 17         // 包装的实例对象的类型
 18         Class<?> beanType = instanceWrapper.getWrappedClass();
 19         if (beanType != NullBean.class) {
 20             mbd.resolvedTargetType = beanType;
 21         }
 22 
 23         // Allow post-processors to modify the merged bean definition.
 24         // 先做同步，然后判断是否有后置处理
 25         synchronized (mbd.postProcessingLock) {
 26             if (!mbd.postProcessed) {
 27                 try {
 28                     // 后置处理修改BeanDefinition
 29                     applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
 30                 } catch (Throwable ex) {
 31                     throw new BeanCreationException(mbd.getResourceDescription(), beanName,
 32                                                     "Post-processing of merged bean definition failed", ex);
 33                 }
 34                 mbd.postProcessed = true;
 35             }
 36         }
 37 
 38         // Eagerly cache singletons to be able to resolve circular references
 39         // even when triggered by lifecycle interfaces like BeanFactoryAware.
 40         // 解决单例模式的循环依赖         // 单例模式               运行循环依赖
 41         boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
 42                 isSingletonCurrentlyInCreation(beanName));// 当前单例bean是否正在被创建
 43         if (earlySingletonExposure) {
 44             if (logger.isDebugEnabled()) {
 45                 logger.debug("Eagerly caching bean ‘" + beanName +
 46                                      "‘ to allow for resolving potential circular references");
 47             }
 48             // 提前将创建的bean实例加入到singletonFactories中
 49             // 为了后期避免循环依赖
 50             addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
 51         }
 52 
 53         // Initialize the bean instance.
 54         // 开始初始化bean实例对象
 55         Object exposedObject = bean;
 56         try {
 57             // 对bean进行填充，主要是进行属性注入，其中，可能存在依赖于其他bean的属性，则会递归初始化依赖bean
 58             populateBean(beanName, mbd, instanceWrapper);
 59             // 进行bean初始化
 60             exposedObject = initializeBean(beanName, exposedObject, mbd);
 61         } catch (Throwable ex) {
 62             if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
 63                 throw (BeanCreationException) ex;
 64             } else {
 65                 throw new BeanCreationException(
 66                         mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
 67             }
 68         }
 69 
 70         // 循环依赖处理
 71         if (earlySingletonExposure) {
 72             // 获取earlySingletonReference
 73             Object earlySingletonReference = getSingleton(beanName, false);
 74             // 只有在循环依赖的情况下，earlySingletonReference才不会为null
 75             if (earlySingletonReference != null) {
 76                 // 如果exposedObject没有在初始化方法中改变，也就是没有被增强
 77                 if (exposedObject == bean) {
 78                     exposedObject = earlySingletonReference;
 79                 } else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) { // 处理依赖
 80                     String[] dependentBeans = getDependentBeans(beanName);
 81                     Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
 82                     for (String dependentBean : dependentBeans) {
 83                         if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
 84                             actualDependentBeans.add(dependentBean);
 85                         }
 86                     }
 87                     if (!actualDependentBeans.isEmpty()) {
 88                         throw new BeanCurrentlyInCreationException(beanName,
 89                                                                    "Bean with name ‘" + beanName + "‘ has been injected into other beans [" +
 90                                                                            StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
 91                                                                            "] in its raw version as part of a circular reference, but has eventually been " +
 92                                                                            "wrapped. This means that said other beans do not use the final version of the " +
 93                                                                            "bean. This is often the result of over-eager type matching - consider using " +
 94                                                                            "‘getBeanNamesOfType‘ with the ‘allowEagerInit‘ flag turned off, for example.");
 95                     }
 96                 }
 97             }
 98         }
 99 
100         // Register bean as disposable.
101         try {
102             // 注册bean
103             registerDisposableBeanIfNecessary(beanName, bean, mbd);
104         } catch (BeanDefinitionValidationException ex) {
105             throw new BeanCreationException(
106                     mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
107         }
108 
109         return exposedObject;
110     }

 1 protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
 2         // Make sure bean class is actually resolved at this point.
 3         // 解析bean，将bean类名解析为class引用
 4         Class<?> beanClass = resolveBeanClass(mbd, beanName);
 5 
 6         if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
 7             throw new BeanCreationException(mbd.getResourceDescription(), beanName,
 8                                             "Bean class isn‘t public, and non-public access not allowed: " + beanClass.getName());
 9         }
10 
11         // 如果存在supplier回调，则使用给定的回调方法初始化策略
12         Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
13         if (instanceSupplier != null) {
14             return obtainFromSupplier(instanceSupplier, beanName);
15         }
16 
17         // 使用FactoryBean的factor-method来创建bean，支持静态工厂和实例工厂
18         if (mbd.getFactoryMethodName() != null) {
19             return instantiateUsingFactoryMethod(beanName, mbd, args);
20         }
21 
22         // Shortcut when re-creating the same bean...
23         boolean resolved = false;
24         boolean autowireNecessary = false;
25         if (args == null) {
26             // 做同步
27             synchronized (mbd.constructorArgumentLock) {
28                 // 如果已缓存的解析构造函数或者工厂方法不为null，则可以利用构造函数解析
29                 // 因为需要根据参数确认到底使用哪个构造函数，该过程比较消耗性能，所以采用缓存机制
30                 if (mbd.resolvedConstructorOrFactoryMethod != null) {
31                     resolved = true;
32                     autowireNecessary = mbd.constructorArgumentsResolved;
33                 }
34             }
35         }
36         // 已经解析好了，直接注入即可
37         if (resolved) {
38             // autowire自动注入，调用构造函数自动注入
39             if (autowireNecessary) {
40                 return autowireConstructor(beanName, mbd, null, null);
41             } else {
42                 // 使用默认构造函数构造
43                 return instantiateBean(beanName, mbd);
44             }
45         }
46 
47         // Need to determine the constructor...
48         // 确定解析的构造函数
49         // 主要是检查已经注册的SmartInstantiationAwareBeanPostProcessor
50         Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
51         // 确定构造方法进行bean创建
52         if (ctors != null ||
53                 mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR ||
54                 mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
55             return autowireConstructor(beanName, mbd, ctors, args);
56         }
57 
58         // 有参数，又没有获取到构造方法，则只能调用无参构造方法来创建实例
59         // 这是一个兜底的方法
60         // No special handling: simply use no-arg constructor.
61         return instantiateBean(beanName, mbd);
62     }

 1 protected BeanWrapper obtainFromSupplier(Supplier<?> instanceSupplier, String beanName) {
 2         // 获得原创建的Bean的对象名
 3         String outerBean = this.currentlyCreatedBean.get();
 4         // 设置新的Bean对象名到currentlyCreatedBean中
 5         this.currentlyCreatedBean.set(beanName);
 6         Object instance;
 7         try {
 8             // 调用Supplier的get(),返回一个Bean对象
 9             instance = instanceSupplier.get();
10         } finally {
11             // 设置原创建的Bean对象名到currentlyCreatedBean中
12             if (outerBean != null) {
13                 this.currentlyCreatedBean.set(outerBean);
14             } else {
15                 this.currentlyCreatedBean.remove();
16             }
17         }
18         // 创建BeanWrapper对象
19         BeanWrapper bw = new BeanWrapperImpl(instance);
20         // 初始化BeanWrapper
21         initBeanWrapper(bw);
22         return bw;
23     }