参考：https://www.cnblogs.com/ITtangtang/p/3978349.html
1. 依赖注入发生的时间
(1）用户第一次通过getBean方法向IoC容器索取Bean时，触发依赖注入
(2) 用户在Bean定义资源中为<Bean>元素配置了lazy-init属性，让容器在解析注册Bean定义时进行预实例化，触发依赖注入
BeanFactory接口定义了Spring IoC容器的基本功能规范，是Spring IoC容器应该遵守的最底层和最基本的规范
BeanFactory接口定义了几个getBean方法，就是用户向IoC容器索取管理的Bean的方法，我们通过分析其子类的具体实现，理解Spring IoC容器在用户索取Bean时如何完成依赖注入。
2. AbstractBeanFactory通过getBean向IoC容器获取被管理的Bean
//获取IoC容器中指定名称的Bean public Object getBean(String name) throws BeansException { //doGetBean才是真正向IoC容器获取被管理Bean的过程 return doGetBean(name, null, null, false); } //获取IoC容器中指定名称和类型的Bean public <T> T getBean(String name, Class<T> requiredType) throws BeansException { //doGetBean才是真正向IoC容器获取被管理Bean的过程 return doGetBean(name, requiredType, null, false); } //获取IoC容器中指定名称和参数的Bean public Object getBean(String name, Object... args) throws BeansException { //doGetBean才是真正向IoC容器获取被管理Bean的过程 return doGetBean(name, null, args, false); } //获取IoC容器中指定名称、类型和参数的Bean public <T> T getBean(String name, Class<T> requiredType, Object... args) throws BeansException { //doGetBean才是真正向IoC容器获取被管理Bean的过程 return doGetBean(name, requiredType, args, false); } //真正实现向IoC容器获取Bean的功能，也是触发依赖注入功能的地方 @SuppressWarnings("unchecked") protected <T> T doGetBean( final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly) throws BeansException { //根据指定的名称获取被管理Bean的名称，剥离指定名称中对容器的相关依赖 //如果指定的是别名，将别名转换为规范的Bean名称 final String beanName = transformedBeanName(name); Object bean; //先从缓存中取是否已经有被创建过的单态类型的Bean，对于单态模式的Bean整 //个IoC容器中只创建一次，不需要重复创建 Object sharedInstance = getSingleton(beanName); //IoC容器创建单态模式Bean实例对象 if (sharedInstance != null && args == null) { if (logger.isDebugEnabled()) { //如果指定名称的Bean在容器中已有单态模式的Bean被创建，直接返回 //已经创建的Bean if (isSingletonCurrentlyInCreation(beanName)) { logger.debug("Returning eagerly cached instance of singleton bean '" + beanName + "' that is not fully initialized yet - a consequence of a circular reference"); } else { logger.debug("Returning cached instance of singleton bean '" + beanName + "'"); } } //获取给定Bean的实例对象，主要是完成FactoryBean的相关处理 //注意：BeanFactory是管理容器中Bean的工厂，而FactoryBean是 //创建创建对象的工厂Bean，两者之间有区别 bean = getObjectForBeanInstance(sharedInstance, name, beanName, null); } else {//缓存没有正在创建的单态模式Bean //缓存中已经有已经创建的原型模式Bean，但是由于循环引用的问题导致实 //例化对象失败 if (isPrototypeCurrentlyInCreation(beanName)) { throw new BeanCurrentlyInCreationException(beanName); } //对IoC容器中是否存在指定名称的BeanDefinition进行检查，首先检查是否 //能在当前的BeanFactory中获取的所需要的Bean，如果不能则委托当前容器 //的父级容器去查找，如果还是找不到则沿着容器的继承体系向父级容器查找 BeanFactory parentBeanFactory = getParentBeanFactory(); //当前容器的父级容器存在，且当前容器中不存在指定名称的Bean if (parentBeanFactory != null && !containsBeanDefinition(beanName)) { //解析指定Bean名称的原始名称 String nameToLookup = originalBeanName(name); if (args != null) { //委派父级容器根据指定名称和显式的参数查找 return (T) parentBeanFactory.getBean(nameToLookup, args); } else { //委派父级容器根据指定名称和类型查找 return parentBeanFactory.getBean(nameToLookup, requiredType); } } //创建的Bean是否需要进行类型验证，一般不需要 if (!typeCheckOnly) { //向容器标记指定的Bean已经被创建 markBeanAsCreated(beanName); } //根据指定Bean名称获取其父级的Bean定义，主要解决Bean继承时子类 //合并父类公共属性问题 final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName); checkMergedBeanDefinition(mbd, beanName, args); //获取当前Bean所有依赖Bean的名称 String[] dependsOn = mbd.getDependsOn(); //如果当前Bean有依赖Bean if (dependsOn != null) { for (String dependsOnBean : dependsOn) { //递归调用getBean方法，获取当前Bean的依赖Bean getBean(dependsOnBean); //把被依赖Bean注册给当前依赖的Bean registerDependentBean(dependsOnBean, beanName); } }
//创建单态模式Bean的实例对象 if (mbd.isSingleton()) { //这里使用了一个匿名内部类，创建Bean实例对象，并且注册给所依赖的对象 sharedInstance = getSingleton(beanName, new ObjectFactory() { public Object getObject() throws BeansException { try { //创建一个指定Bean实例对象，如果有父级继承，则合并子//类和父类的定义 return createBean(beanName, mbd, args); } catch (BeansException ex) { //显式地从容器单态模式Bean缓存中清除实例对象 destroySingleton(beanName); throw ex; } } }); //获取给定Bean的实例对象 bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd); } //IoC容器创建原型模式Bean实例对象 else if (mbd.isPrototype()) { //原型模式(Prototype)是每次都会创建一个新的对象 Object prototypeInstance = null; try { //回调beforePrototypeCreation方法，默认的功能是注册当前创//建的原型对象 beforePrototypeCreation(beanName); //创建指定Bean对象实例 prototypeInstance = createBean(beanName, mbd, args); } finally { //回调afterPrototypeCreation方法，默认的功能告诉IoC容器指//定Bean的原型对象不再创建了 afterPrototypeCreation(beanName); } //获取给定Bean的实例对象 bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd); } //要创建的Bean既不是单态模式，也不是原型模式，则根据Bean定义资源中 //配置的生命周期范围，选择实例化Bean的合适方法，这种在Web应用程序中 //比较常用，如：request、session、application等生命周期 else { String scopeName = mbd.getScope(); final Scope scope = this.scopes.get(scopeName); //Bean定义资源中没有配置生命周期范围，则Bean定义不合法 if (scope == null) { throw new IllegalStateException("No Scope registered for scope '" + scopeName + "'"); } try { //这里又使用了一个匿名内部类，获取一个指定生命周期范围的实例 Object scopedInstance = scope.get(beanName, new ObjectFactory() { public Object getObject() throws BeansException { beforePrototypeCreation(beanName); try { return createBean(beanName, mbd, args); } finally { afterPrototypeCreation(beanName); } } }); //获取给定Bean的实例对象 bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd); } catch (IllegalStateException ex) { throw new BeanCreationException(beanName, "Scope '" + scopeName + "' is not active for the current thread; " + "consider defining a scoped proxy for this bean if you intend to refer to it from a singleton", ex); } } } //对创建的Bean实例对象进行类型检查 if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) { throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass()); } return (T) bean; }
按照bean定义的不同，如果是单态模式，则在创建之前先在缓存中查找，如果是原型模式，则每次都创建一个实例对象。除此之外，还可以扩展为指定的生命周期范围。
对象的创建过程是实现了ObjectFactory接口的匿名内部类的createBean方法完成，具体的创建交给实现类AbstractAutowireCapableBeanFactory完成
3. AbstractAutowireCapableBeanFactory创建Bean实例对象：
//创建Bean实例对象 protected Object createBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) throws BeanCreationException { if (logger.isDebugEnabled()) { logger.debug("Creating instance of bean '" + beanName + "'"); } //判断需要创建的Bean是否可以实例化，即是否可以通过当前的类加载器加载 resolveBeanClass(mbd, beanName); //校验和准备Bean中的方法覆盖 try { mbd.prepareMethodOverrides(); } catch (BeanDefinitionValidationException ex) { throw new BeanDefinitionStoreException(mbd.getResourceDescription(), beanName, "Validation of method overrides failed", ex); } try { //如果Bean配置了初始化前和初始化后的处理器，则试图返回一个需要创建//Bean的代理对象 Object bean = resolveBeforeInstantiation(beanName, mbd); if (bean != null) { return bean; } } catch (Throwable ex) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "BeanPostProcessor before instantiation of bean failed", ex); } //创建Bean的入口 Object beanInstance = doCreateBean(beanName, mbd, args); if (logger.isDebugEnabled()) { logger.debug("Finished creating instance of bean '" + beanName + "'"); } return beanInstance; } //真正创建Bean的方法 protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) { //封装被创建的Bean对象 BeanWrapper instanceWrapper = null; if (mbd.isSingleton()){//单态模式的Bean，先从容器中缓存中获取同名Bean instanceWrapper = this.factoryBeanInstanceCache.remove(beanName); } if (instanceWrapper == null) { //创建实例对象 instanceWrapper = createBeanInstance(beanName, mbd, args); //创建实例对象 } final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null); //获取实例化对象的类型 Class beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null); //调用PostProcessor后置处理器 synchronized (mbd.postProcessingLock) { if (!mbd.postProcessed) { applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName); mbd.postProcessed = true; } } // Eagerly cache singletons to be able to resolve circular references //向容器中缓存单态模式的Bean对象，以防循环引用 boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences && isSingletonCurrentlyInCreation(beanName)); if (earlySingletonExposure) { if (logger.isDebugEnabled()) { logger.debug("Eagerly caching bean '" + beanName + "' to allow for resolving potential circular references"); } //这里是一个匿名内部类，为了防止循环引用，尽早持有对象的引用 addSingletonFactory(beanName, new ObjectFactory() { public Object getObject() throws BeansException { return getEarlyBeanReference(beanName, mbd, bean); } }); } //Bean对象的初始化，依赖注入在此触发 //这个exposedObject在初始化完成之后返回作为依赖注入完成后的Bean Object exposedObject = bean; try { //将Bean实例对象封装，并且Bean定义中配置的属性值赋值给实例对象 populateBean(beanName, mbd, instanceWrapper); //将属性赋值给实例对象 if (exposedObject != null) { //初始化Bean对象 exposedObject = initializeBean(beanName, exposedObject, mbd); } } catch (Throwable ex) { if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) { throw (BeanCreationException) ex; } else { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex); } } if (earlySingletonExposure) { //获取指定名称的已注册的单态模式Bean对象 Object earlySingletonReference = getSingleton(beanName, false); if (earlySingletonReference != null) { //根据名称获取的以注册的Bean和正在实例化的Bean是同一个 if (exposedObject == bean) { //当前实例化的Bean初始化完成 exposedObject = earlySingletonReference; } //当前Bean依赖其他Bean，并且当发生循环引用时不允许新创建实例对象 else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) { String[] dependentBeans = getDependentBeans(beanName); Set<String> actualDependentBeans = new LinkedHashSet<String>(dependentBeans.length); //获取当前Bean所依赖的其他Bean for (String dependentBean : dependentBeans) { //对依赖Bean进行类型检查 if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) { actualDependentBeans.add(dependentBean); } } if (!actualDependentBeans.isEmpty()) { throw new BeanCurrentlyInCreationException(beanName, "Bean with name '" + beanName + "' has been injected into other beans [" + StringUtils.collectionToCommaDelimitedString(actualDependentBeans) + "] in its raw version as part of a circular reference, but has eventually been " + "wrapped. This means that said other beans do not use the final version of the " + "bean. This is often the result of over-eager type matching - consider using " + "'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example."); } } } } //注册完成依赖注入的Bean try { registerDisposableBeanIfNecessary(beanName, bean, mbd); } catch (BeanDefinitionValidationException ex) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex); } return exposedObject; }
具体的依赖注入实现在一下两个方法中：
（1）createBeanInstance(): 生成Bean包含的java对象实例
（2）populateBean(): 对Bean属性的依赖注入进行处理
4. createBeanInstance()方法创建bean的java实例对象
//创建Bean的实例对象 protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, Object[] args) { //检查确认Bean是可实例化的 Class beanClass = resolveBeanClass(mbd, beanName); //使用工厂方法对Bean进行实例化 if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Bean class isn't public, and non-public access not allowed: " + beanClass.getName()); } if (mbd.getFactoryMethodName() != null) { //调用工厂方法实例化（分为静态工厂方法和工厂实例） return instantiateUsingFactoryMethod(beanName, mbd, args); //工厂方法实例化 } //构造器进行实例化 boolean resolved = false;
//是否可以自动匹配构造器 boolean autowireNecessary = false; if (args == null) { synchronized (mbd.constructorArgumentLock) { if (mbd.resolvedConstructorOrFactoryMethod != null) { resolved = true; autowireNecessary = mbd.constructorArgumentsResolved; } } } if (resolved) { if (autowireNecessary) { //根据参数类型自动匹配Bean的构造方法 return autowireConstructor(beanName, mbd, null, null); //使用了构造器方法的自动装配，根据参数类型匹配Bean的构造方法 } else { //使用默认的无参构造方法实例化 return instantiateBean(beanName, mbd); } } //使用Bean的构造方法进行实例化 Constructor[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName); if (ctors != null || mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR || mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) { //使用容器的自动装配特性，调用匹配的构造方法实例化 return autowireConstructor(beanName, mbd, ctors, args); } //使用默认的无参构造方法实例化 return instantiateBean(beanName, mbd); //默认无参的构造方法 } //使用默认的无参构造方法实例化Bean对象 protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) { try { Object beanInstance; final BeanFactory parent = this; //获取系统的安全管理接口，JDK标准的安全管理API if (System.getSecurityManager() != null) { //这里是一个匿名内置类，根据实例化策略创建实例对象 beanInstance = AccessController.doPrivileged(new PrivilegedAction<Object>() { public Object run() { return getInstantiationStrategy().instantiate(mbd, beanName, parent); } }, getAccessControlContext()); } else { //将实例化的对象封装起来 beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent); } BeanWrapper bw = new BeanWrapperImpl(beanInstance); initBeanWrapper(bw); return bw; } catch (Throwable ex) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex); } }
创建方式：
（1）工厂方法：静态工厂方法和实例工厂
（2）自动装配：调用参数匹配的构造方法（有参构造器）
（3）默认的无参构造方法：JDK反射(Bean定义中没有方法被覆盖) 或者 CGLIB
一、通过反射：
- 反射获取构造器方法
- 通过 构造方法.newInstance(arg)获取实例
//使用初始化策略实例化Bean对象 public Object instantiate(RootBeanDefinition beanDefinition, String beanName, BeanFactory owner) { //如果Bean定义中没有方法覆盖，则就不需要CGLIB父类类的方法 if (beanDefinition.getMethodOverrides().isEmpty()) { Constructor<?> constructorToUse; synchronized (beanDefinition.constructorArgumentLock) { //获取对象的构造方法或工厂方法 constructorToUse = (Constructor<?>) beanDefinition.resolvedConstructorOrFactoryMethod; //如果没有构造方法且没有工厂方法 if (constructorToUse == null) { //使用JDK的反射机制，判断要实例化的Bean是否是接口 final Class clazz = beanDefinition.getBeanClass(); if (clazz.isInterface()) { throw new BeanInstantiationException(clazz, "Specified class is an interface"); } try { if (System.getSecurityManager() != null) { //这里是一个匿名内置类，使用反射机制获取Bean的构造方法 constructorToUse = AccessController.doPrivileged(new PrivilegedExceptionAction<Constructor>() { public Constructor run() throws Exception { return clazz.getDeclaredConstructor((Class[]) null); } }); } else { constructorToUse = clazz.getDeclaredConstructor((Class[]) null); } beanDefinition.resolvedConstructorOrFactoryMethod = constructorToUse; } catch (Exception ex) { throw new BeanInstantiationException(clazz, "No default constructor found", ex); } } } //使用BeanUtils实例化，通过反射机制调用”构造方法.newInstance(arg)”来进行实例化 return BeanUtils.instantiateClass(constructorToUse); } else { //使用CGLIB来实例化对象 return instantiateWithMethodInjection(beanDefinition, beanName, owner); } }
二、通过CGLIB
//使用CGLIB进行Bean对象实例化 public Object instantiate(Constructor ctor, Object[] args) { //CGLIB中的类 Enhancer enhancer = new Enhancer(); //将Bean本身作为其基类 enhancer.setSuperclass(this.beanDefinition.getBeanClass()); enhancer.setCallbackFilter(new CallbackFilterImpl()); enhancer.setCallbacks(new Callback[] { NoOp.INSTANCE, new LookupOverrideMethodInterceptor(), new ReplaceOverrideMethodInterceptor() }); //使用CGLIB的create方法生成实例对象 return (ctor == null) ? enhancer.create() : enhancer.create(ctor.getParameterTypes(), args); }
至此，我们获得了Bean对象的封装类BeanWrapper，第一阶段完成
5. populateBean方法对Bean属性的依赖注入
//将Bean属性设置到生成的实例对象上 protected void populateBean(String beanName, AbstractBeanDefinition mbd, BeanWrapper bw) { //获取容器在解析Bean定义资源时为BeanDefiniton中设置的属性值 PropertyValues pvs = mbd.getPropertyValues(); //实例对象为null if (bw == null) { //属性值不为空 if (!pvs.isEmpty()) { throw new BeanCreationException( mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance"); } else { //实例对象为null，属性值也为空，不需要设置属性值，直接返回 return; } } //在设置属性之前调用Bean的PostProcessor后置处理器 boolean continueWithPropertyPopulation = true; if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) { for (BeanPostProcessor bp : getBeanPostProcessors()) { if (bp instanceof InstantiationAwareBeanPostProcessor) { InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) { continueWithPropertyPopulation = false; break; } } } } if (!continueWithPropertyPopulation) { return; } //依赖注入开始，首先处理autowire自动装配的注入 if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME || mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) { MutablePropertyValues newPvs = new MutablePropertyValues(pvs); //对autowire自动装配的处理，根据Bean名称自动装配注入 if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) { autowireByName(beanName, mbd, bw, newPvs); } //根据Bean类型自动装配注入 if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) { autowireByType(beanName, mbd, bw, newPvs); } pvs = newPvs; } //检查容器是否持有用于处理单态模式Bean关闭时的后置处理器 boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors(); //Bean实例对象没有依赖，即没有继承基类 boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE); if (hasInstAwareBpps || needsDepCheck) { //从实例对象中提取属性描述符 PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw); if (hasInstAwareBpps) { for (BeanPostProcessor bp : getBeanPostProcessors()) { if (bp instanceof InstantiationAwareBeanPostProcessor) { InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; //使用BeanPostProcessor处理器处理属性值 pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName); if (pvs == null) { return; } } } } if (needsDepCheck) { //为要设置的属性进行依赖检查 checkDependencies(beanName, mbd, filteredPds, pvs); } } //对属性进行注入 applyPropertyValues(beanName, mbd, bw, pvs); } //解析并注入依赖属性的过程 protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) { if (pvs == null || pvs.isEmpty()) { return; } //封装属性值 MutablePropertyValues mpvs = null; List<PropertyValue> original; if (System.getSecurityManager()!= null) { if (bw instanceof BeanWrapperImpl) { //设置安全上下文，JDK安全机制 ((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext()); } } if (pvs instanceof MutablePropertyValues) { mpvs = (MutablePropertyValues) pvs; //属性值已经转换 if (mpvs.isConverted()) { try { //为实例化对象设置属性值 bw.setPropertyValues(mpvs); return; } catch (BeansException ex) { throw new BeanCreationException( mbd.getResourceDescription(), beanName, "Error setting property values", ex); } } //获取属性值对象的原始类型值 original = mpvs.getPropertyValueList(); } else { original = Arrays.asList(pvs.getPropertyValues()); } //获取用户自定义的类型转换 TypeConverter converter = getCustomTypeConverter(); if (converter == null) { converter = bw; } //创建一个Bean定义属性值解析器，将Bean定义中的属性值解析为Bean实例对象 //的实际值 BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter); //为属性的解析值创建一个拷贝，将拷贝的数据注入到实例对象中 List<PropertyValue> deepCopy = new ArrayList<PropertyValue>(original.size()); boolean resolveNecessary = false; for (PropertyValue pv : original) { //属性值不需要转换
if (pv.isConverted()) { deepCopy.add(pv); } //属性值需要转换 else { String propertyName = pv.getName(); //原始的属性值，即转换之前的属性值 Object originalValue = pv.getValue(); //转换属性值，例如将引用转换为IoC容器中实例化对象引用 Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue); //解析属性值 //转换之后的属性值 Object convertedValue = resolvedValue; //属性值是否可以转换 boolean convertible = bw.isWritableProperty(propertyName) && !PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName); if (convertible) { //使用用户自定义的类型转换器转换属性值 convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter); } //存储转换后的属性值，避免每次属性注入时的转换工作 if (resolvedValue == originalValue) { if (convertible) { //设置属性转换之后的值 pv.setConvertedValue(convertedValue); } deepCopy.add(pv); } //属性是可转换的，且属性原始值是字符串类型，且属性的原始类型值不是 //动态生成的字符串，且属性的原始值不是集合或者数组类型 else if (convertible && originalValue instanceof TypedStringValue && !((TypedStringValue) originalValue).isDynamic() && !(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) { pv.setConvertedValue(convertedValue); deepCopy.add(pv); } else { resolveNecessary = true; //重新封装属性的值 deepCopy.add(new PropertyValue(pv, convertedValue)); } } } if (mpvs != null && !resolveNecessary) { //标记属性值已经转换过 mpvs.setConverted(); } //进行属性依赖注入 try { bw.setPropertyValues(new MutablePropertyValues(deepCopy)); //属性注入 } catch (BeansException ex) { throw new BeanCreationException( mbd.getResourceDescription(), beanName, "Error setting property values", ex); } }
（1）先处理自动装配的注入（1. 根据名称 2. 根据类型）
（2）根据属性值的类型不同
- 属性值类型不需要转换时，直接准备依赖注入
- 属性值需要进行类型转换，如对其他对象的引用，首先解析属性值，然后对解析后的属性值依赖注入
一、BeanDefinitionValueResolver类的resolveValueIfNecessary() 解析属性值：
//解析属性值，对注入类型进行转换 public Object resolveValueIfNecessary(Object argName, Object value) { //对引用类型的属性进行解析 if (value instanceof RuntimeBeanReference) { RuntimeBeanReference ref = (RuntimeBeanReference) value; //调用引用类型属性的解析方法 return resolveReference(argName, ref); } //对属性值是引用容器中另一个Bean名称的解析 else if (value instanceof RuntimeBeanNameReference) { String refName = ((RuntimeBeanNameReference) value).getBeanName(); refName = String.valueOf(evaluate(refName)); //从容器中获取指定名称的Bean if (!this.beanFactory.containsBean(refName)) { throw new BeanDefinitionStoreException( "Invalid bean name '" + refName + "' in bean reference for " + argName); } return refName; } //对Bean类型属性的解析，主要是Bean中的内部类 else if (value instanceof BeanDefinitionHolder) { BeanDefinitionHolder bdHolder = (BeanDefinitionHolder) value; return resolveInnerBean(argName, bdHolder.getBeanName(), bdHolder.getBeanDefinition()); } else if (value instanceof BeanDefinition) { BeanDefinition bd = (BeanDefinition) value; return resolveInnerBean(argName, "(inner bean)", bd); } //对集合数组类型的属性解析 else if (value instanceof ManagedArray) { ManagedArray array = (ManagedArray) value; //获取数组的类型 Class elementType = array.resolvedElementType; if (elementType == null) { //获取数组元素的类型 String elementTypeName = array.getElementTypeName(); if (StringUtils.hasText(elementTypeName)) { try { //使用反射机制创建指定类型的对象 elementType = ClassUtils.forName(elementTypeName, this.beanFactory.getBeanClassLoader()); array.resolvedElementType = elementType; } catch (Throwable ex) { throw new BeanCreationException( this.beanDefinition.getResourceDescription(), this.beanName, "Error resolving array type for " + argName, ex); } } //没有获取到数组的类型，也没有获取到数组元素的类型，则直接设置数 //组的类型为Object else { elementType = Object.class; } } //创建指定类型的数组 return resolveManagedArray(argName, (List<?>) value, elementType); } //解析list类型的属性值 else if (value instanceof ManagedList) { return resolveManagedList(argName, (List<?>) value); } //解析set类型的属性值 else if (value instanceof ManagedSet) { return resolveManagedSet(argName, (Set<?>) value); } //解析map类型的属性值 else if (value instanceof ManagedMap) { return resolveManagedMap(argName, (Map<?, ?>) value); } //解析props类型的属性值，props其实就是key和value均为字符串的map else if (value instanceof ManagedProperties) { Properties original = (Properties) value; //创建一个拷贝，用于作为解析后的返回值 Properties copy = new Properties(); for (Map.Entry propEntry : original.entrySet()) { Object propKey = propEntry.getKey(); Object propValue = propEntry.getValue(); if (propKey instanceof TypedStringValue) { propKey = evaluate((TypedStringValue) propKey); } if (propValue instanceof TypedStringValue) { propValue = evaluate((TypedStringValue) propValue); } copy.put(propKey, propValue); } return copy; } //解析字符串类型的属性值 else if (value instanceof TypedStringValue) { TypedStringValue typedStringValue = (TypedStringValue) value; Object valueObject = evaluate(typedStringValue); try { //获取属性的目标类型 Class<?> resolvedTargetType = resolveTargetType(typedStringValue); if (resolvedTargetType != null) { //对目标类型的属性进行解析，递归调用 return this.typeConverter.convertIfNecessary(valueObject, resolvedTargetType); } //没有获取到属性的目标对象，则按Object类型返回 else { return valueObject; } } catch (Throwable ex) { throw new BeanCreationException( this.beanDefinition.getResourceDescription(), this.beanName, "Error converting typed String value for " + argName, ex); } } else { return evaluate(value); } } //解析引用类型的属性值 private Object resolveReference(Object argName, RuntimeBeanReference ref) { try { //获取引用的Bean名称 String refName = ref.getBeanName(); refName = String.valueOf(evaluate(refName)); //如果引用的对象在父类容器中，则从父类容器中获取指定的引用对象 if (ref.isToParent()) { if (this.beanFactory.getParentBeanFactory() == null) { throw new BeanCreationException( this.beanDefinition.getResourceDescription(), this.beanName, "Can't resolve reference to bean '" + refName + "' in parent factory: no parent factory available"); } return this.beanFactory.getParentBeanFactory().getBean(refName); } //从当前的容器中获取指定的引用Bean对象，如果指定的Bean没有被实例化 //则会递归触发引用Bean的初始化和依赖注入 else { Object bean = this.beanFactory.getBean(refName); //将当前实例化对象的依赖引用对象 this.beanFactory.registerDependentBean(refName, this.beanName); return bean; } } catch (BeansException ex) { throw new BeanCreationException( this.beanDefinition.getResourceDescription(), this.beanName, "Cannot resolve reference to bean '" + ref.getBeanName() + "' while setting " + argName, ex); } } //解析array类型的属性 private Object resolveManagedArray(Object argName, List<?> ml, Class elementType) { //创建一个指定类型的数组，用于存放和返回解析后的数组 Object resolved = Array.newInstance(elementType, ml.size()); for (int i = 0; i < ml.size(); i++) { //递归解析array的每一个元素，并将解析后的值设置到resolved数组中，索引为i Array.set(resolved, i, resolveValueIfNecessary(new KeyedArgName(argName, i), ml.get(i))); } return resolved; } //解析list类型的属性 private List resolveManagedList(Object argName, List<?> ml) { List<Object> resolved = new ArrayList<Object>(ml.size()); for (int i = 0; i < ml.size(); i++) { //递归解析list的每一个元素 resolved.add( resolveValueIfNecessary(new KeyedArgName(argName, i), ml.get(i))); } return resolved; } //解析set类型的属性 private Set resolveManagedSet(Object argName, Set<?> ms) { Set<Object> resolved = new LinkedHashSet<Object>(ms.size()); int i = 0; //递归解析set的每一个元素 for (Object m : ms) { resolved.add(resolveValueIfNecessary(new KeyedArgName(argName, i), m)); i++; } return resolved; } //解析map类型的属性 private Map resolveManagedMap(Object argName, Map<?, ?> mm) { Map<Object, Object> resolved = new LinkedHashMap<Object, Object>(mm.size()); //递归解析map中每一个元素的key和value for (Map.Entry entry : mm.entrySet()) { Object resolvedKey = resolveValueIfNecessary(argName, entry.getKey()); Object resolvedValue = resolveValueIfNecessary( new KeyedArgName(argName, entry.getKey()), entry.getValue()); resolved.put(resolvedKey, resolvedValue); } return resolved; }
对引用类型的解析：获取引用的Bean名称，向容器获取Bean以触发依赖Bean的依赖注入，向BeanFactory中设置两者的依赖关系
对集合类型的解析：创建对应的数据结构，并递归解析集合的内部元素
二、将解析完成的属性设置到Bean实例中
//实现属性依赖注入功能 private void setPropertyValue(PropertyTokenHolder tokens, PropertyValue pv) throws BeansException { //PropertyTokenHolder主要保存属性的名称、路径，以及集合的size等信息 String propertyName = tokens.canonicalName; String actualName = tokens.actualName; //keys是用来保存集合类型属性的size if (tokens.keys != null) { //将属性信息拷贝 PropertyTokenHolder getterTokens = new PropertyTokenHolder(); getterTokens.canonicalName = tokens.canonicalName; getterTokens.actualName = tokens.actualName; getterTokens.keys = new String[tokens.keys.length - 1]; System.arraycopy(tokens.keys, 0, getterTokens.keys, 0, tokens.keys.length - 1); Object propValue; try { //获取属性值，该方法内部使用JDK的内省( Introspector)机制，调用属性//的getter(readerMethod)方法，获取属性的值 propValue = getPropertyValue(getterTokens); } catch (NotReadablePropertyException ex) { throw new NotWritablePropertyException(getRootClass(), this.nestedPath + propertyName, "Cannot access indexed value in property referenced " + "in indexed property path '" + propertyName + "'", ex); } //获取集合类型属性的长度 String key = tokens.keys[tokens.keys.length - 1]; if (propValue == null) { throw new NullValueInNestedPathException(getRootClass(), this.nestedPath + propertyName, "Cannot access indexed value in property referenced " + "in indexed property path '" + propertyName + "': returned null"); } //注入array类型的属性值 else if (propValue.getClass().isArray()) { //获取属性的描述符 PropertyDescriptor pd = getCachedIntrospectionResults().getPropertyDescriptor(actualName); //获取数组的类型 Class requiredType = propValue.getClass().getComponentType(); //获取数组的长度 int arrayIndex = Integer.parseInt(key); Object oldValue = null; try { //获取数组以前初始化的值 if (isExtractOldValueForEditor()) { oldValue = Array.get(propValue, arrayIndex); } //将属性的值赋值给数组中的元素 Object convertedValue = convertIfNecessary(propertyName, oldValue, pv.getValue(), requiredType, new PropertyTypeDescriptor(pd, new MethodParameter(pd.getReadMethod(), -1), requiredType)); Array.set(propValue, arrayIndex, convertedValue); } catch (IndexOutOfBoundsException ex) { throw new InvalidPropertyException(getRootClass(), this.nestedPath + propertyName, "Invalid array index in property path '" + propertyName + "'", ex); } } //注入list类型的属性值 else if (propValue instanceof List) { PropertyDescriptor pd = getCachedIntrospectionResults().getPropertyDescriptor(actualName); //获取list集合的类型 Class requiredType = GenericCollectionTypeResolver.getCollectionReturnType( pd.getReadMethod(), tokens.keys.length); List list = (List) propValue; //获取list集合的size int index = Integer.parseInt(key); Object oldValue = null; if (isExtractOldValueForEditor() && index < list.size()) { oldValue = list.get(index); } //获取list解析后的属性值 Object convertedValue = convertIfNecessary(propertyName, oldValue, pv.getValue(), requiredType, new PropertyTypeDescriptor(pd, new MethodParameter(pd.getReadMethod(), -1), requiredType)); if (index < list.size()) { //为list属性赋值 list.set(index, convertedValue); } //如果list的长度大于属性值的长度，则多余的元素赋值为null else if (index >= list.size()) { for (int i = list.size(); i < index; i++) { try { list.add(null); } catch (NullPointerException ex) { throw new InvalidPropertyException(getRootClass(), this.nestedPath + propertyName, "Cannot set element with index " + index + " in List of size " + list.size() + ", accessed using property path '" + propertyName + "': List does not support filling up gaps with null elements"); } } list.add(convertedValue); } } //注入map类型的属性值 else if (propValue instanceof Map) { PropertyDescriptor pd = getCachedIntrospectionResults().getPropertyDescriptor(actualName); //获取map集合key的类型 Class mapKeyType = GenericCollectionTypeResolver.getMapKeyReturnType( pd.getReadMethod(), tokens.keys.length); //获取map集合value的类型 Class mapValueType = GenericCollectionTypeResolver.getMapValueReturnType( pd.getReadMethod(), tokens.keys.length); Map map = (Map) propValue; //解析map类型属性key值 Object convertedMapKey = convertIfNecessary(null, null, key, mapKeyType, new PropertyTypeDescriptor(pd, new MethodParameter(pd.getReadMethod(), -1), mapKeyType)); Object oldValue = null; if (isExtractOldValueForEditor()) { oldValue = map.get(convertedMapKey); } //解析map类型属性value值 Object convertedMapValue = convertIfNecessary( propertyName, oldValue, pv.getValue(), mapValueType, new TypeDescriptor(new MethodParameter(pd.getReadMethod(), -1, tokens.keys.length + 1))); //将解析后的key和value值赋值给map集合属性 map.put(convertedMapKey, convertedMapValue); } else { throw new InvalidPropertyException(getRootClass(), this.nestedPath + propertyName, "Property referenced in indexed property path '" + propertyName + "' is neither an array nor a List nor a Map; returned value was [" + pv.getValue() + "]"); } } //对非集合类型的属性注入 else { PropertyDescriptor pd = pv.resolvedDescriptor; if (pd == null || !pd.getWriteMethod().getDeclaringClass().isInstance(this.object)) { pd = getCachedIntrospectionResults().getPropertyDescriptor(actualName); //无法获取到属性名或者属性没有提供setter(写方法)方法 if (pd == null || pd.getWriteMethod() == null) { //如果属性值是可选的，即不是必须的，则忽略该属性值 if (pv.isOptional()) { logger.debug("Ignoring optional value for property '" + actualName + "' - property not found on bean class [" + getRootClass().getName() + "]"); return; } //如果属性值是必须的，则抛出无法给属性赋值，因为每天提供setter方法异常 else { PropertyMatches matches = PropertyMatches.forProperty(propertyName, getRootClass()); throw new NotWritablePropertyException( getRootClass(), this.nestedPath + propertyName, matches.buildErrorMessage(), matches.getPossibleMatches()); } } pv.getOriginalPropertyValue().resolvedDescriptor = pd; } Object oldValue = null; try { Object originalValue = pv.getValue(); Object valueToApply = originalValue; if (!Boolean.FALSE.equals(pv.conversionNecessary)) { if (pv.isConverted()) { valueToApply = pv.getConvertedValue(); } else { if (isExtractOldValueForEditor() && pd.getReadMethod() != null) { //获取属性的getter方法(读方法)，JDK内省机制 final Method readMethod = pd.getReadMethod(); //如果属性的getter方法不是public访问控制权限的，即访问控制权限比较严格， //则使用JDK的反射机制强行访问非public的方法(暴力读取属性值) if (!Modifier.isPublic(readMethod.getDeclaringClass().getModifiers()) && !readMethod.isAccessible()) { if (System.getSecurityManager()!= null) { //匿名内部类，根据权限修改属性的读取控制限制 AccessController.doPrivileged(new PrivilegedAction<Object>() { public Object run() { readMethod.setAccessible(true); return null; } }); } else { readMethod.setAccessible(true); } } try { //属性没有提供getter方法时，调用潜在的读取属性值//的方法，获取属性值 if (System.getSecurityManager() != null) { oldValue = AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() { public Object run() throws Exception { return readMethod.invoke(object); } }, acc); } else { oldValue = readMethod.invoke(object); } } catch (Exception ex) { if (ex instanceof PrivilegedActionException) { ex = ((PrivilegedActionException) ex).getException(); } if (logger.isDebugEnabled()) { logger.debug("Could not read previous value of property '" + this.nestedPath + propertyName + "'", ex); } } } //设置属性的注入值 valueToApply = convertForProperty(propertyName, oldValue, originalValue, pd); } pv.getOriginalPropertyValue().conversionNecessary = (valueToApply != originalValue); } //根据JDK的内省机制，获取属性的setter(写方法)方法 final Method writeMethod = (pd instanceof GenericTypeAwarePropertyDescriptor ? ((GenericTypeAwarePropertyDescriptor) pd).getWriteMethodForActualAccess() : pd.getWriteMethod()); //如果属性的setter方法是非public，即访问控制权限比较严格，则使用JDK的反射机制， //强行设置setter方法可访问(暴力为属性赋值) if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers()) && !writeMethod.isAccessible()) { //如果使用了JDK的安全机制，则需要权限验证 if (System.getSecurityManager()!= null) { AccessController.doPrivileged(new PrivilegedAction<Object>() { public Object run() { writeMethod.setAccessible(true); return null; } }); } else { writeMethod.setAccessible(true); } } final Object value = valueToApply; if (System.getSecurityManager() != null) { try { //将属性值设置到属性上去 AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() { public Object run() throws Exception { writeMethod.invoke(object, value); return null; } }, acc); } catch (PrivilegedActionException ex) { throw ex.getException(); } } else { writeMethod.invoke(this.object, value); } } catch (TypeMismatchException ex) { throw ex; } catch (InvocationTargetException ex) { PropertyChangeEvent propertyChangeEvent = new PropertyChangeEvent(this.rootObject, this.nestedPath + propertyName, oldValue, pv.getValue()); if (ex.getTargetException() instanceof ClassCastException) { throw new TypeMismatchException(propertyChangeEvent, pd.getPropertyType(), ex.getTargetException()); } else { throw new MethodInvocationException(propertyChangeEvent, ex.getTargetException()); } } catch (Exception ex) { PropertyChangeEvent pce = new PropertyChangeEvent(this.rootObject, this.nestedPath + propertyName, oldValue, pv.getValue()); throw new MethodInvocationException(pce, ex); } } }
（1）对于集合类型的属性，将属性值解析为目标类型的集合后直接赋值给属性
（2）对非集合类型的属性，使用JDK反射和内省机制，通过设置属性的getter(reader method)方法获取指定属性注入以前的值，同时调用属性的setter方法(writer method)为属性设置注入后的值。
至此，依赖注入便完成了。
现在Spring IoC容器中管理了一系列靠依赖关系联系起来的Bean，程序不需要应用自己手动创建所需的对象，Spring IoC容器会在我们使用的时候自动为我们创建，并且为我们注入好相关的依赖，这就是Spring核心功能的控制反转和依赖注入的相关功能。
总结：
1.发生时机
1.关闭了懒加载，在IOC容器初始化解析Bean定义时预实例化
2.第一次getBean
2.getBean流程
1.单例模式先从缓存中获取，有则返回
2.如果有父容器并且本身没有这个Bean所属的BeanDefinition，交给父容器获取
3.将依赖的Bean注册给当前Bean，只是将名字维护到Map中<String/*主BeanName*/,Set<String>/*依赖的BeanName*/>
4.创建单例Bean(createBean)
5.创建原型Bean(createBean)
6.根据Scope创建对应的Bean
3.createBean流程
1.如果Bean配置了初始化前和初始化后的处理器，返回一个Bean的代理对象(resolveBeforeInstantiation方法)
2.doCreateBean方法，1.创建实例 2.依赖注入 3.初始化
2.1创建对象实例 createBeanInstance方法
2.2调用PostProcessor后置处理器(applyMergedBeanDefinitionPostProcessors方法)
2.3向容器缓存单理模式的Bean对象防止循环应用
2.4依赖注入populateBean
2.5初始化Bean对象initializeBean
2.6注册Bean
4.createBeanInstance方法
1.使用工厂方法实例化(bean配置了FactoryMethodName)
2.使用自动装配实例化(bean配置了autowire属性为constructor)
3.默认使用无参构造方法实例化
3.1使用JDK反射，要求Bean定义中没有方法被覆盖
3.1.1从缓存中获取已解析的对象的构造方法或工厂方法
3.1.2如果没有，使用反射机制获取Bean的构造方法并存入缓存
3.1.3通过构造方法进行实例化
3.2使用CGLIB
3.2.1将Bean作为基类生成增强类，使用create方法创建
5.populateBean方法
1.从BeanDefinition中获取Bean中的属性
2.首先处理自动装配注入属性(如果bean配置了autowire属性为byName，byType)
3.一般注入applyPropertyValues
6.applyPropertyValues方法
1.如果属性值已经做过转化，则给对象设置
2.如果没有转化需要先转化(resolveValueIfNecessary方法)，可以使用用户自定义的类型转化
3.属性注入(setPropertyValues方法)
7. resolveValueIfNecessary方法
1.解析引用类型属性：get(Bean)从容器中找到依赖的Bean，并在BeanFactory中设置两者的依赖关系
2.解析集合/数组：创建对应的数据结构（因为在beanDefinition中存的封装过的），递归解析集合的内部元素
8.setPropertyValues方法
1.对于集合类型的属性，将集合中的值解析为对应目标类型后赋值给属性
2.对于非集合类型的属性，使用set方法注入，访问权限不足使用JDK反射