createBean源码：
java
/**
* Central method of this class: creates a bean instance,
* populates the bean instance, applies post-processors, etc.
* @see #doCreateBean
*/
@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
if (logger.isTraceEnabled()) {
logger.trace("Creating instance of bean '" + beanName + "'");
}
RootBeanDefinition mbdToUse = mbd;
// Make sure bean class is actually resolved at this point, and
// clone the bean definition in case of a dynamically resolved Class
// which cannot be stored in the shared merged bean definition.
// 马上就要实例化Bean了，确保beanClass被加载了
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 {
// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
// 实例化前
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 {
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
if (logger.isTraceEnabled()) {
logger.trace("Finished creating instance of bean '" + beanName + "'");
}
return beanInstance;
}
catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
// A previously detected exception with proper bean creation context already,
// or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
throw ex;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
}
}
/**
* Resolve the bean class for the specified bean definition,
* resolving a bean class name into a Class reference (if necessary)
* and storing the resolved Class in the bean definition for further use.
* @param mbd the merged bean definition to determine the class for
* @param beanName the name of the bean (for error handling purposes)
* @param typesToMatch the types to match in case of internal type matching purposes
* (also signals that the returned {@code Class} will never be exposed to application code)
* @return the resolved bean class (or {@code null} if none)
* @throws CannotLoadBeanClassException if we failed to load the class
*/
@Nullable
protected Class<?> resolveBeanClass(RootBeanDefinition mbd, String beanName, Class<?>... typesToMatch)
throws CannotLoadBeanClassException {
try {
// 如果beanClass被加载了，return (this.beanClass instanceof Class);
if (mbd.hasBeanClass()) {
return mbd.getBeanClass();
}
// 如果beanClass没有被加载
if (System.getSecurityManager() != null) {
return AccessController.doPrivileged((PrivilegedExceptionAction<Class<?>>)
() -> doResolveBeanClass(mbd, typesToMatch), getAccessControlContext());
}
else {
return doResolveBeanClass(mbd, typesToMatch);
}
}
catch (PrivilegedActionException pae) {
ClassNotFoundException ex = (ClassNotFoundException) pae.getException();
throw new CannotLoadBeanClassException(mbd.getResourceDescription(), beanName, mbd.getBeanClassName(), ex);
}
catch (ClassNotFoundException ex) {
throw new CannotLoadBeanClassException(mbd.getResourceDescription(), beanName, mbd.getBeanClassName(), ex);
}
catch (LinkageError err) {
throw new CannotLoadBeanClassException(mbd.getResourceDescription(), beanName, mbd.getBeanClassName(), err);
}
}
@Nullable
private Class<?> doResolveBeanClass(RootBeanDefinition mbd, Class<?>... typesToMatch)
throws ClassNotFoundException {
ClassLoader beanClassLoader = getBeanClassLoader();
ClassLoader dynamicLoader = beanClassLoader;
boolean freshResolve = false;
if (!ObjectUtils.isEmpty(typesToMatch)) {
// When just doing type checks (i.e. not creating an actual instance yet),
// use the specified temporary class loader (e.g. in a weaving scenario).
ClassLoader tempClassLoader = getTempClassLoader();
if (tempClassLoader != null) {
dynamicLoader = tempClassLoader;
freshResolve = true;
if (tempClassLoader instanceof DecoratingClassLoader) {
DecoratingClassLoader dcl = (DecoratingClassLoader) tempClassLoader;
for (Class<?> typeToMatch : typesToMatch) {
dcl.excludeClass(typeToMatch.getName());
}
}
}
}
String className = mbd.getBeanClassName();
if (className != null) {
// 解析Spring表达式，有可能直接返回了一个Class对象
Object evaluated = evaluateBeanDefinitionString(className, mbd);
if (!className.equals(evaluated)) {
// A dynamically resolved expression, supported as of 4.2...
if (evaluated instanceof Class) {
return (Class<?>) evaluated;
}
else if (evaluated instanceof String) {
className = (String) evaluated;
freshResolve = true;
}
else {
throw new IllegalStateException("Invalid class name expression result: " + evaluated);
}
}
if (freshResolve) {
// When resolving against a temporary class loader, exit early in order
// to avoid storing the resolved Class in the bean definition.
if (dynamicLoader != null) {
try {
return dynamicLoader.loadClass(className);
}
catch (ClassNotFoundException ex) {
if (logger.isTraceEnabled()) {
logger.trace("Could not load class [" + className + "] from " + dynamicLoader + ": " + ex);
}
}
}
return ClassUtils.forName(className, dynamicLoader);
}
}
// Resolve regularly, caching the result in the BeanDefinition...
return mbd.resolveBeanClass(beanClassLoader);
}
/**
* Apply before-instantiation post-processors, resolving whether there is a
* before-instantiation shortcut for the specified bean.
* @param beanName the name of the bean
* @param mbd the bean definition for the bean
* @return the shortcut-determined bean instance, or {@code null} if none
*/
@Nullable
protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
Object bean = null;
if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
// Make sure bean class is actually resolved at this point.
// synthetic表示合成，如果某些Bean式合成的，那么则不会经过BeanPostProcessor的处理
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
Class<?> targetType = determineTargetType(beanName, mbd);
if (targetType != null) {
bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
if (bean != null) {
bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
}
}
}
mbd.beforeInstantiationResolved = (bean != null);
}
return bean;
}
/**
* Apply InstantiationAwareBeanPostProcessors to the specified bean definition
* (by class and name), invoking their {@code postProcessBeforeInstantiation} methods.
* <p>Any returned object will be used as the bean instead of actually instantiating
* the target bean. A {@code null} return value from the post-processor will
* result in the target bean being instantiated.
* @param beanClass the class of the bean to be instantiated
* @param beanName the name of the bean
* @return the bean object to use instead of a default instance of the target bean, or {@code null}
* @see InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation
*/
@Nullable
protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
for (InstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().instantiationAware) {
Object result = bp.postProcessBeforeInstantiation(beanClass, beanName);
if (result != null) {
// 注意：返回的类型没判断，可以和参数beanClass类型不一样
return result; // 有结果就返回，没有结果循环。实例化前取第一个
}
}
return null;
}
@Override
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor processor : getBeanPostProcessors()) {
Object current = processor.postProcessAfterInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}doCreateBean源码：
java
/**
* Actually create the specified bean. Pre-creation processing has already happened
* at this point, e.g. checking {@code postProcessBeforeInstantiation} callbacks.
* <p>Differentiates between default bean instantiation, use of a
* factory method, and autowiring a constructor.
* @param beanName the name of the bean
* @param mbd the merged bean definition for the bean
* @param args explicit arguments to use for constructor or factory method invocation
* @return a new instance of the bean
* @throws BeanCreationException if the bean could not be created
* @see #instantiateBean
* @see #instantiateUsingFactoryMethod
* @see #autowireConstructor
*/
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
// 实例化bean
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
// 有可能在本Bean创建之前，就有其他Bean把当前Bean给创建出来了（比如依赖注入过程中）
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
// 创建Bean实例
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
// 后置处理合并后的BeanDefinition
// 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;
}
}
// 为了解决循环依赖提前缓存单例创建工厂
// 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.isTraceEnabled()) {
logger.trace("Eagerly caching bean '" + beanName +
"' to allow for resolving potential circular references");
}
// 循环依赖-添加到三级缓存
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
// 属性填充
populateBean(beanName, mbd, instanceWrapper);
// 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)) {
// beanName被哪些bean依赖了，现在发现beanName所对应的bean对象发生了改变，那么则会报错
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 " +
"'getBeanNamesForType' 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;
}总结BeanPostProcessor
1、InstantiationAwareBeanPostProcessor.postProcessBeforeInstantiation()
2、实例化
3、MergedBeanDefinitionPostProcessor.postProcessMergedBeanDefinition()
4、InstantiationAwareBeanPostProcessor.postProcessAfterInstantiation()
5、自动注入
6、InstantiationAwareBeanPostProcessor.postProcessProperties()
7、Aware对象
8、BeanPostProcessor.postProcessBeforeInitialization()
9、初始化
10、BeanPostProcessor.postProcessAfterInitialization()