0 前言
IoC容器主要分为两个阶段：IoC容器启动和依赖注入。
在上节
Spring原理与源码分析系列（四）- Spring IoC源码分析（上） 我们已经从源码的角度分析了IoC容器的启动过程，本篇将要讲述依赖注入过程的源码分析。
二、IoC容器的依赖注入
在IoC容器的初始化完成后，就已经在容器内建立了BeanDefinition数据映射。
接下来就需要开始依赖注入了。
首先通过getBean()触发依赖注入这个过程，这个过程主要分为两个步骤：
- 1 Bean的对象实例化（Instantiate the Bean）：createBeanInstance（）；
- 2 对象关系的依赖注入：populate（）。
下面来看看具体的实现过程。
首先是用户调用getBean()方法，这个方法是依赖注入的入口，会触发依赖注入的过程。
AbstractBeanFactory.java
Override
public Object getBean(String name) throws BeansException {
return doGetBean(name, null, null, false);
}
@Override
public <T> T getBean(String name, @Nullable Class<T> requiredType) throws BeansException {
return doGetBean(name, requiredType, null, false);
}
@Override
public Object getBean(String name, Object... args) throws BeansException {
return doGetBean(name, null, args, false);
}
public <T> T getBean(String name, @Nullable Class<T> requiredType, @Nullable Object... args)
throws BeansException {
return doGetBean(name, requiredType, args, false);
}实际取得Bean的地方，也是依赖注入发生的地方：
AbstractBeanFactory.java
//实际取得Bean的地方，触发依赖注入发生的地方
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
final String beanName = transformedBeanName(name);
Object bean;
// 先从缓存中取得Bean。如果是单例，就不需要再创建
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {
if (logger.isDebugEnabled()) {
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 + "'");
}
}
//完成FactoryBean的相关处理
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
// Fail if we're already creating this bean instance: // We're assumably within a circular reference.
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
//检查IoC容器中beanName对应的BeanDefinition是否存在，如果当前容器不存在，
// 则到双亲BeanFactory（parentBeanFactory）去寻找；
//如果当前双亲BeanFactory不存在，就顺着双亲BeanFactory链一直向上查找
// Check if bean definition exists in this factory.
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {
return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
nameToLookup, requiredType, args, typeCheckOnly);
}
else if (args != null) {
// 在双亲BeanFactory中查找
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
}
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}
try {
//根据beanName取得BeanDefinition
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// 获得当前Bean的所有依赖Bean。触发getBean的递归调用
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dep : dependsOn) {
if (isDependent(beanName, dep)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
}
registerDependentBean(dep, beanName);
getBean(dep);
}
}
// 在getSingleton调用ObjectFactory中的createBean（），创建Singleton Bean的实例
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, () -> { try { //触发Bean的创建 return createBean(beanName, mbd, args); } catch (BeansException ex) { // Explicitly remove instance from singleton cache: It might have been put there // eagerly by the creation process, to allow for circular reference resolution. // Also remove any beans that received a temporary reference to the bean. destroySingleton(beanName); throw ex; } }); bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd); } //创建Prototype Bean的实例 else if (mbd.isPrototype()) { // It's a prototype -> create a new instance.
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
//触发Bean的创建
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
//获取指定Scope类型的Bean
else {
String scopeName = mbd.getScope();
final Scope scope = this.scopes.get(scopeName);
if (scope == null) {
throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
}
try {
Object scopedInstance = scope.get(beanName, () -> { beforePrototypeCreation(beanName); try { //触发Bean的创建 return createBean(beanName, mbd, args); } finally { afterPrototypeCreation(beanName); } }); 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); } } } catch (BeansException ex) { cleanupAfterBeanCreationFailure(beanName); throw ex; } } // 对创建的Bean进行类型检查。如果没有问题，则返回新创建的Bean。这个Bean已经包含了依赖关系 if (requiredType != null && !requiredType.isInstance(bean)) { try { T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType); if (convertedBean == null) { throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass()); } return convertedBean; } catch (TypeMismatchException ex) { if (logger.isDebugEnabled()) { logger.debug("Failed to convert bean '" + name + "' to required type '" + ClassUtils.getQualifiedName(requiredType) + "'", ex); } throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass()); } } return (T) bean; }可以看到，在用户调用getBean()方法后，会调用doGetBean()方法，然后再调用createBean()方法进行Bean的创建以及依赖注入过程。
接下来我们就来看 看Bean是如何被创建以及对象关系的依赖注入的。
1 Bean的对象实例化（Instantiate the Bean）
当调用createBean()方法时，会进入
AbstractAutowireCapableBeanFactory中。
AbstractAutowireCapableBeanFactory.java
@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
if (logger.isDebugEnabled()) {
logger.debug("Creating instance of bean '" + beanName + "'");
}
RootBeanDefinition mbdToUse = mbd;
// 判断需要创建的Bean是否可以实例化（接口不能被实例化）以及该类能否被类加载器加载
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
// Prepare method overrides.
try {
mbdToUse.prepareMethodOverrides();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
beanName, "Validation of method overrides failed", ex);
}
try {
// 如果Bean配置了BeanPostProcessors，则返回一个proxy
Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
if (bean != null) {
return bean;
}
}
catch (Throwable ex) {
throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
"BeanPostProcessor before instantiation of bean failed", ex);
}
try {
//这里是调用真正创建Bean的地方
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
if (logger.isDebugEnabled()) {
logger.debug("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
}
catch (BeanCreationException ex) {
// A previously detected exception with proper bean creation context already...
throw ex;
}
catch (ImplicitlyAppearedSingletonException ex) {
// An IllegalStateException to be communicated up to DefaultSingletonBeanRegistry...
throw ex;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
}
}在createBean（）中，调用doCreateBean（）来具体创建Bean。
进入doCreateBean（），来看看真正创建Bean的地方：
AbstractAutowireCapableBeanFactory.java
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
// Bean的实例化（Instantiate）
//BeanWrapper是用来持有创建出来的Bean对象的
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
//如果是Singleton，先把缓存中的同名Bean清除
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
//这里是创建Bean的地方：createBeanInstance（）
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
final Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
// Allow post-processors to modify the merged bean definition.
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}
// Eagerly cache singletons to be able to resolve circular references
// even when triggered by lifecycle interfaces like BeanFactoryAware.
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");
}
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean)); } // 对Bean的初始化，依赖注入一般发生在这里。 Object exposedObject = bean; try { //populateBean：对象间依赖关系的处理 populateBean(beanName, mbd, instanceWrapper); //initializeBean：Bean的初始化 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) { Object earlySingletonReference = getSingleton(beanName, false); if (earlySingletonReference != null) { if (exposedObject == bean) { exposedObject = earlySingletonReference; } else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) { String[] dependentBeans = getDependentBeans(beanName); Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length); for (String dependentBean : dependentBeans) { 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."); } } } } // Register bean as disposable. try { registerDisposableBeanIfNecessary(beanName, bean, mbd); } catch (BeanDefinitionValidationException ex) { throw new BeanCreationException( mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex); } return exposedObject; }在这个方法中，有两个重要方法调用需要关注：
- createBeanInstance（）：对Bean包含的对象进行实例化的地方，返回的是一个BeanWrapper（为什么返回的BeanWrapper而不是Bean，是因为BeanWrapper方便后续对Bean的设值操作）；
- populateBean（）：Bean创建后，需要进行对象间的依赖关系的处理。
AbstractAutowireCapableBeanFactory.java
// Bean包含的Java对象的生成，有3种方法：工厂方法，构造器函数实例化，默认构造函数实例化（SimpleInstantiationStrategy提供了反射和CGLIB两种方式）
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// 看Bean能否实例化（接口不能被实例化）
Class<?> beanClass = resolveBeanClass(mbd, beanName);
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());
}
Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
if (instanceSupplier != null) {
return obtainFromSupplier(instanceSupplier, beanName);
}
if (mbd.getFactoryMethodName() != null) {
//使用工厂方法实例化
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
// Shortcut when re-creating the same bean...
boolean resolved = false;
boolean autowireNecessary = false;
if (args == null) {
synchronized (mbd.constructorArgumentLock) {
if (mbd.resolvedConstructorOrFactoryMethod != null) {
resolved = true;
autowireNecessary = mbd.constructorArgumentsResolved;
}
}
}
if (resolved) {
if (autowireNecessary) {
return autowireConstructor(beanName, mbd, null, null);
}
else {
return instantiateBean(beanName, mbd);
}
}
//使用构造函数进行实例化
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null ||
mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
return autowireConstructor(beanName, mbd, ctors, args);
}
//使用默认构造函数对Bean实例化(using default constructor)
return instantiateBean(beanName, mbd);
}
这个过程主要是Bean包含对象的实例化的生成，主要有3种方法：
- 工厂方法
- 构造器函数实例化
- 默认构造函数实例化（提供了反射和CGLIB两种方法）
其中，instantiateBean（）是最常见的Bean实例化的方法。
AbstractAutowireCapableBeanFactory.java
/**
* Instantiate the given bean using its default constructor.
* @param beanName the name of the bean
* @param mbd the bean definition for the bean
* @return a BeanWrapper for the new instance
*/
protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
try {
Object beanInstance;
final BeanFactory parent = this;
if (System.getSecurityManager() != null) {
beanInstance = AccessController.doPrivileged((PrivilegedAction<Object>) () -> getInstantiationStrategy().instantiate(mbd, beanName, parent), getAccessControlContext()); } else { //使用默认的实例化策略，默认采用的是CglibSubclassingInstantiationStrategy，即CGLIB对Bean进行实例化 beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent); } //实例化后，返回对应的BeanWrapper类 BeanWrapper bw = new BeanWrapperImpl(beanInstance); initBeanWrapper(bw); return bw; } catch (Throwable ex) { throw new BeanCreationException( mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex); } }上面采用的是默认构造函数的实例化。在这个过程中：
beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);getInstantiationStrategy()默认返回的 是CglibSubclassingInstantiationStrategy，即默认使用CGLIB对Bean进行实例化。
AbstractAutowireCapableBeanFactory.java
//返回的instantiationStrategy默认是CglibSubclassingInstantiationStrategy
protected InstantiationStrategy getInstantiationStrategy() {
return this.instantiationStrategy;
}
private InstantiationStrategy instantiationStrategy = new CglibSubclassingInstantiationStrategy();CglibSubclassingInstantiationStrategy继承了SimpleInstantiationStrategy类，所以在了解CGLIB是如何实例化Bean对象的时候，我们首先进入SimpleInstantiationStrategy类中看看这个实例化策略提供了哪些策略。
SimpleInstantiationStrategy.java
@Override
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
// Don't override the class with CGLIB if no overrides.
if (!bd.hasMethodOverrides()) {
Constructor<?> constructorToUse;
synchronized (bd.constructorArgumentLock) {
//这里取得指定的构造器或者对象的工厂方法来对Bean进行实例化
constructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod;
if (constructorToUse == null) {
final Class<?> clazz = bd.getBeanClass();
if (clazz.isInterface()) {
throw new BeanInstantiationException(clazz, "Specified class is an interface");
}
try {
if (System.getSecurityManager() != null) {
constructorToUse = AccessController.doPrivileged(
(PrivilegedExceptionAction<Constructor<?>>) () -> clazz.getDeclaredConstructor());
}
else {
constructorToUse = clazz.getDeclaredConstructor();
}
bd.resolvedConstructorOrFactoryMethod = constructorToUse;
}
catch (Throwable ex) {
throw new BeanInstantiationException(clazz, "No default constructor found", ex);
}
}
}
//使用BeanUtils（反射）进行Bean的实例化，具体调用时通过构造器来实例化Bean的
return BeanUtils.instantiateClass(constructorToUse);
}
else {
// 使用Cglib进行Bean的实例化
return instantiateWithMethodInjection(bd, beanName, owner);
}
}SimpleInstantiationStrategy是Spring生成Bean对象的默认类。类中提供了两种实例化Bean对象的方法：
- BeanUtils（使用了JVM的反射）
- CGLIB
下面看看这两个实例化Bean对象方法是如何实现的：
BeanUtils
通过
return BeanUtils.instantiateClass(constructorToUse);
进入BeanUtils类中的instantiateClass（）方法。
BeanUtils.java
/**
* Convenience method to instantiate a class using the given constructor.
* <p>Note that this method tries to set the constructor accessible if given a
* non-accessible (that is, non-public) constructor, and supports Kotlin classes
* with optional parameters and default values.
* @param ctor the constructor to instantiate
* @param args the constructor arguments to apply (use {@code null} for an unspecified
* parameter if needed for Kotlin classes with optional parameters and default values)
* @return the new instance
* @throws BeanInstantiationException if the bean cannot be instantiated
* @see Constructor#newInstance
*/
public static <T> T instantiateClass(Constructor<T> ctor, Object... args) throws BeanInstantiationException {
Assert.notNull(ctor, "Constructor must not be null");
try {
//ReflectionUtils：使用反射，调用构造函数创建运行时对象
ReflectionUtils.makeAccessible(ctor);
//（Kotlin？WTF，此处是比较新的源码了。。。）调用的ctor.newInstance(args)，即使用构造函数
return (KotlinDetector.isKotlinType(ctor.getDeclaringClass()) ?
KotlinDelegate.instantiateClass(ctor, args) : ctor.newInstance(args));
}
catch (InstantiationException ex) {
throw new BeanInstantiationException(ctor, "Is it an abstract class?", ex);
}
catch (IllegalAccessException ex) {
throw new BeanInstantiationException(ctor, "Is the constructor accessible?", ex);
}
catch (IllegalArgumentException ex) {
throw new BeanInstantiationException(ctor, "Illegal arguments for constructor", ex);
}
catch (InvocationTargetException ex) {
throw new BeanInstantiationException(ctor, "Constructor threw exception", ex.getTargetException());
}
}可以看到，BeanUtils采用的是反射调用构造函数来创建Bean对象。
CGLIB
再进入CglibSubclassingInstantiationStrategy类，看看CGLIB是如何进行Bean实例化的。
CglibSubclassingInstantiationStrategy.java
public Object instantiate(@Nullable Constructor<?> ctor, @Nullable Object... args) {
//使用Enhancer生成字节码
Class<?> subclass = createEnhancedSubclass(this.beanDefinition);
Object instance;
// 没传构造方法，直接实例化
if (ctor == null) {
instance = BeanUtils.instantiateClass(subclass); } else { try { // 实例化对象 Constructor<?> enhancedSubclassConstructor = subclass.getConstructor(ctor.getParameterTypes()); instance = enhancedSubclassConstructor.newInstance(args); } catch (Exception ex) { throw new BeanInstantiationException(this.beanDefinition.getBeanClass(), "Failed to invoke constructor for CGLIB enhanced subclass [" + subclass.getName() + "]", ex); } } // SPR-10785: set callbacks directly on the instance instead of in the // enhanced class (via the Enhancer) in order to avoid memory leaks. Factory factory = (Factory) instance; factory.setCallbacks(new Callback[] {NoOp.INSTANCE, new LookupOverrideMethodInterceptor(this.beanDefinition, this.owner), new ReplaceOverrideMethodInterceptor(this.beanDefinition, this.owner)}); return instance; } //生成Enhancer对象，并为Enhancer对象设置上生成Java对象的参数，如基类，回调方法等 private Class<?> createEnhancedSubclass(RootBeanDefinition beanDefinition) { Enhancer enhancer = new Enhancer(); enhancer.setSuperclass(beanDefinition.getBeanClass()); enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE); if (this.owner instanceof ConfigurableBeanFactory) { ClassLoader cl = ((ConfigurableBeanFactory) this.owner).getBeanClassLoader(); enhancer.setStrategy(new ClassLoaderAwareGeneratorStrategy(cl)); } enhancer.setCallbackFilter(new MethodOverrideCallbackFilter(beanDefinition)); enhancer.setCallbackTypes(CALLBACK_TYPES); return enhancer.createClass(); } }走到这一步，Bean创建及实例化的过程就已经结束。Bean对象生成后，需要把这些Bean对象的依赖关系设置好，完成整个依赖注入的过程。这就需要用的populate（）方法。
2 对象关系的依赖注入
在类AbstractAutowireCapableBeanFactory的doCreateBean（）方法中，我们接触过populateBean（）方法：
AbstractAutowireCapableBeanFactory.java
//对Bean的初始化，依赖注入一般发生在这里。
Object exposedObject = bean;
try {
//populateBean：对象间依赖关系的处理
populateBean(beanName, mbd, instanceWrapper);
//initializeBean：Bean的初始化
exposedObject = initializeBean(beanName, exposedObject, mbd);
}现在进入populateBean方法中看下具体的实现：
populateBean():
AbstractAutowireCapableBeanFactory.java
protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
if (bw == null) {
if (mbd.hasPropertyValues()) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
}
else {
// //若实例对象为null 且属性值为空，跳过。Skip property population phase for null instance.
return;
}
}
boolean continueWithPropertyPopulation = true;
//调用Bean的后置处理器:BeanPostProcessor
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;
}
//获取容器在解析Bean定义的时候的属性值
PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);
//根据XML设置的autowire来进行依赖注入。注这里的autowire与注解@Autowire是不同的
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
// AUTOWIRE_BY_NAME：根据Bean name 和 setter自动装配
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd, bw, newPvs);
}
// AUTOWIRE_BY_TYPE：根据Bean type自动装配
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
autowireByType(beanName, mbd, bw, newPvs);
}
pvs = newPvs;
}
boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);
if (hasInstAwareBpps || needsDepCheck) {
if (pvs == null) {
pvs = mbd.getPropertyValues();
}
PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
if (hasInstAwareBpps) {
for (BeanPostProcessor bp : getBeanPostProcessors()) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvs == null) {
return;
}
}
}
}
if (needsDepCheck) {
checkDependencies(beanName, mbd, filteredPds, pvs);
}
}
if (pvs != null) {
//这里是对属性进行注入的地方
applyPropertyValues(beanName, mbd, bw, pvs);
}
}根据上面代码可以看到，在populateBean（）方法中，首先要用ean的后置处理器:BeanPostProcessor对Bean进行处理，然后获取Bean的所有属性值，如果在XML配置文件中配置有autowire="byName/byType"项，就调用
autowireByName(beanName, mbd, bw, newPvs);
和
autowireByType(beanName, mbd, bw, newPvs);
对其依赖注入。注意，这里的AUTOWIRE是配置文件中的，与注解@Autowire是不同的。由于不推荐在配置文件中使用autowire="byName/byType"， 所以也不分析这两个方法autowireByType和autowireByName。
接着就调用applyPropertyValues()方法对属性进行注入：
AbstractAutowireCapableBeanFactory.java
protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
//pvs就是获取的属性值
if (pvs.isEmpty()) {
return;
}
//用MutablePropertyValues封装属性值
MutablePropertyValues mpvs = null;
List<PropertyValue> original;
if (System.getSecurityManager() != null) {
if (bw instanceof BeanWrapperImpl) {
((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext());
}
}
if (pvs instanceof MutablePropertyValues) {
mpvs = (MutablePropertyValues) pvs;
//如果mpvs已经转换过，就直接进行属性注入
if (mpvs.isConverted()) {
// Shortcut: use the pre-converted values as-is.
try {
//属性注入,稍后分析这个过程
bw.setPropertyValues(mpvs);
return;
}
catch (BeansException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Error setting property values", ex);
}
}
original = mpvs.getPropertyValueList();
}
else {
original = Arrays.asList(pvs.getPropertyValues());
}
//需要转换属性，获取自定义转换
TypeConverter converter = getCustomTypeConverter();
if (converter == null) {
converter = bw;
}
//创建属性解析器，对属性进行解析
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<>(original.size());
boolean resolveNecessary = false;
for (PropertyValue pv : original) {
//不需要转换
if (pv.isConverted()) {
deepCopy.add(pv);
}
else {
String propertyName = pv.getName();
//原始值
Object originalValue = pv.getValue();
//转换后的值：resolveValueIfNecessary这个就是解析
Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
Object convertedValue = resolvedValue;
boolean convertible = bw.isWritableProperty(propertyName) &&
!PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
if (convertible) {
convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
}
// Possibly store converted value in merged bean definition,
// in order to avoid re-conversion for every created bean instance.
if (resolvedValue == originalValue) {
if (convertible) {
pv.setConvertedValue(convertedValue);
}
deepCopy.add(pv);
}
else if (convertible && originalValue instanceof TypedStringValue &&
!((TypedStringValue) originalValue).isDynamic() &&
!(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) {
pv.setConvertedValue(convertedValue);
deepCopy.add(pv);
}
else {
resolveNecessary = true;
deepCopy.add(new PropertyValue(pv, convertedValue));
}
}
}
if (mpvs != null && !resolveNecessary) {
mpvs.setConverted();
}
// Set our (possibly massaged) deep copy.
try {
//将转换后的拷贝的数据注入到对象当中
bw.setPropertyValues(new MutablePropertyValues(deepCopy));
}
catch (BeansException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Error setting property values", ex);
}
}在applyPropertyValues()方法中，首先看属性是否已经是符合注入标准的类型MutablePropertyValues，如果是就直接开始注入。否则，需要调用resolveValueIfNecessary（）方法对属性进行解析。
什么时候需要解析？
<bean id="" class="">
<property name="" ref=""/>
<property name="">
<props></..>
</property >
<property name="">
<list></..>
</property >
</bean>当配置文件的Bean的属性中有ref，props，list，map等属性时需要调用resolveValueIfNecessary（）对各种属性进行解析。之前在BeanDefinition载入和解析过程中分析这个过程，如果Bean有ref，list,map等属性的时候，需要解析成对应的RuntimeBeanReference，MangedList，MangedMap等数据结构。现在需要再解析回去。
让我们看看resolveValueIfNecessary（）是如何将RuntimeBeanReference，MangedList，MangedMap等数据结构解析成Spring能够认识的内部结构的。
BeanDefinitionValueResolver.java
@Nullable
public Object resolveValueIfNecessary(Object argName, @Nullable Object value) {
//对引用的类型的属性进行解析，对应ref属性
if (value instanceof RuntimeBeanReference) {
RuntimeBeanReference ref = (RuntimeBeanReference) value;
return resolveReference(argName, ref);
}
//对引用另一个Bean的解析
else if (value instanceof RuntimeBeanNameReference) {
String refName = ((RuntimeBeanNameReference) value).getBeanName();
refName = String.valueOf(doEvaluate(refName));
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) {
// Resolve BeanDefinitionHolder: contains BeanDefinition with name and aliases.
BeanDefinitionHolder bdHolder = (BeanDefinitionHolder) value;
return resolveInnerBean(argName, bdHolder.getBeanName(), bdHolder.getBeanDefinition());
}
else if (value instanceof BeanDefinition) {
// Resolve plain BeanDefinition, without contained name: use dummy name.
BeanDefinition bd = (BeanDefinition) value;
String innerBeanName = "(inner bean)" + BeanFactoryUtils.GENERATED_BEAN_NAME_SEPARATOR +
ObjectUtils.getIdentityHexString(bd);
return resolveInnerBean(argName, innerBeanName, bd);
}
//对集合数组类型（Array）的属性解析
else if (value instanceof ManagedArray) {
// May need to resolve contained runtime references.
ManagedArray array = (ManagedArray) value;
Class<?> elementType = array.resolvedElementType;
if (elementType == null) {
String elementTypeName = array.getElementTypeName();
if (StringUtils.hasText(elementTypeName)) {
try {
elementType = ClassUtils.forName(elementTypeName, this.beanFactory.getBeanClassLoader());
array.resolvedElementType = elementType;
}
catch (Throwable ex) {
// Improve the message by showing the context.
throw new BeanCreationException(
this.beanDefinition.getResourceDescription(), this.beanName,
"Error resolving array type for " + argName, ex);
}
}
else {
elementType = Object.class;
}
}
return resolveManagedArray(argName, (List<?>) value, elementType);
}
//对List类型的属性解析
else if (value instanceof ManagedList) {
// May need to resolve contained runtime references.
return resolveManagedList(argName, (List<?>) value);
}
//对Set类型的属性解析
else if (value instanceof ManagedSet) {
// May need to resolve contained runtime references.
return resolveManagedSet(argName, (Set<?>) value);
}
//对Map类型的属性解析
else if (value instanceof ManagedMap) {
// May need to resolve contained runtime references.
return resolveManagedMap(argName, (Map<?, ?>) value);
}
//对Properties类型的属性解析
else if (value instanceof ManagedProperties) {
Properties original = (Properties) value;
Properties copy = new Properties();
original.forEach((propKey, propValue) -> {
if (propKey instanceof TypedStringValue) {
propKey = evaluate((TypedStringValue) propKey);
}
if (propValue instanceof TypedStringValue) {
propValue = evaluate((TypedStringValue) propValue);
}
if (propKey == null || propValue == null) {
throw new BeanCreationException(
this.beanDefinition.getResourceDescription(), this.beanName,
"Error converting Properties key/value pair for " + argName + ": resolved to null");
}
copy.put(propKey, propValue);
});
return copy;
}
//对String类型的属性解析
else if (value instanceof TypedStringValue) {
// Convert value to target type here.
TypedStringValue typedStringValue = (TypedStringValue) value;
Object valueObject = evaluate(typedStringValue);
try {
Class<?> resolvedTargetType = resolveTargetType(typedStringValue);
if (resolvedTargetType != null) {
return this.typeConverter.convertIfNecessary(valueObject, resolvedTargetType);
}
else {
return valueObject;
}
}
catch (Throwable ex) {
// Improve the message by showing the context.
throw new BeanCreationException(
this.beanDefinition.getResourceDescription(), this.beanName,
"Error converting typed String value for " + argName, ex);
}
}
else if (value instanceof NullBean) {
return null;
}
else {
return evaluate(value);
}
}其中，我们可以看看对引用类型和List类型是如何解析的：
BeanDefinitionValueResolver.java
@Nullable
private Object resolveReference(Object argName, RuntimeBeanReference ref) {
try {
//从RuntimeBeanReference获取refrence名字，RuntimeBeanReference是在BeanDefinition根据配置生成的
Object bean;
String refName = ref.getBeanName();
refName = String.valueOf(doEvaluate(refName));
//如果ref是在双亲IoC容器中，就在双亲IoC容器中查找
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");
}
//在当前容器查找
bean = this.beanFactory.getParentBeanFactory().getBean(refName);
}
else {
//触发依赖注入的发生
bean = this.beanFactory.getBean(refName);
this.beanFactory.registerDependentBean(refName, this.beanName);
}
if (bean instanceof NullBean) {
bean = null;
}
return bean;
}
catch (BeansException ex) {
throw new BeanCreationException(
this.beanDefinition.getResourceDescription(), this.beanName,
"Cannot resolve reference to bean '" + ref.getBeanName() + "' while setting " + argName, ex);
}
}BeanDefinitionValueResolver.java
private List<?> resolveManagedList(Object argName, List<?> ml) {
List<Object> resolved = new ArrayList<>(ml.size());
for (int i = 0; i < ml.size(); i++) {
//递归，对List元素进行解析
resolved.add(
resolveValueIfNecessary(new KeyedArgName(argName, i), ml.get(i)));
}
return resolved;
}其余的解析过程与上类似，在此不一一解释。
在完成上述步骤后，就已经解析完了Bean中property元素的值，然后就进行依赖注入的过程。
setPropertyValues():属性注入到对象中
AbstractPropertyAccessor.java
@Override
public void setPropertyValues(PropertyValues pvs, boolean ignoreUnknown, boolean ignoreInvalid)
throws BeansException {
List<PropertyAccessException> propertyAccessExceptions = null;
//得到属性列表
List<PropertyValue> propertyValues = (pvs instanceof MutablePropertyValues ?
((MutablePropertyValues) pvs).getPropertyValueList() : Arrays.asList(pvs.getPropertyValues()));
for (PropertyValue pv : propertyValues) {
try {
// 这里是属性注入的地方
setPropertyValue(pv);
}
catch (NotWritablePropertyException ex) {
if (!ignoreUnknown) {
throw ex;
}
// Otherwise, just ignore it and continue...
}
catch (NullValueInNestedPathException ex) {
if (!ignoreInvalid) {
throw ex;
}
// Otherwise, just ignore it and continue...
}
catch (PropertyAccessException ex) {
if (propertyAccessExceptions == null) {
propertyAccessExceptions = new LinkedList<>();
}
propertyAccessExceptions.add(ex);
}
}
// If we encountered individual exceptions, throw the composite exception.
if (propertyAccessExceptions != null) {
PropertyAccessException[] paeArray =
propertyAccessExceptions.toArray(new PropertyAccessException[propertyAccessExceptions.size()]);
throw new PropertyBatchUpdateException(paeArray);
}
}上面代码中可以看到，先得到Bean相关的所有属性列表：
List<PropertyValue> propertyValues = (pvs instanceof MutablePropertyValues ?
((MutablePropertyValues) pvs).getPropertyValueList() : Arrays.asList(pvs.getPropertyValues()));
再对每个属性进行注入：
setPropertyValue(pv);
这里setPropertyValue（）的最终实现在BeanWrapper 的子类BeanWrapperImpl类中（我们之前提过BeanWrapper，这个类就是对Bean的封装，方便set，get操作）：
BeanWrapperImpl.java
@Override
public void setValue(final @Nullable Object value) throws Exception {
final Method writeMethod = (this.pd instanceof GenericTypeAwarePropertyDescriptor ?
((GenericTypeAwarePropertyDescriptor) this.pd).getWriteMethodForActualAccess() :
this.pd.getWriteMethod());
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> { ReflectionUtils.makeAccessible(writeMethod); return null; }); try { AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> writeMethod.invoke(getWrappedInstance(), value), acc); } catch (PrivilegedActionException ex) { throw ex.getException(); } } else { ReflectionUtils.makeAccessible(writeMethod); //使用反射 将value值通过set方法注入 writeMethod.invoke(getWrappedInstance(), value); } } }可以看到，在获取属性值value后就通过反射method.invoke()将其注入。这样就完成了IoC容器依赖注入的所有过程。
