01.createBean方法
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.
// 锁定class，根据设置的class属性或者根据className来解析class
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
// 进行条件筛选，重新赋值RootBeanDefinition,并设置BeanClass属性
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
// 重新创建一个RootBeanDefinition对象
mbdToUse = new RootBeanDefinition(mbd);
// 设置BeanClass属性值
mbdToUse.setBeanClass(resolvedClass);
}
// Prepare method overrides.
// 验证及准备覆盖的方法,lookup-method replace-method，当需要创建的bean对象中包含了lookup-method和replace-method标签的时候，会产生覆盖操作
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.
// 给BeanPostProcessors一个机会来返回代理来替代真正的实例，应用实例化前的前置处理器,用户自定义动态代理的方式，针对于当前的被代理类需要经过标准的代理流程来创建对象
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 {
// 实际创建bean的调用
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);
}
}
02.这段
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.
// 锁定class，根据设置的class属性或者根据className来解析class
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
// 进行条件筛选，重新赋值RootBeanDefinition,并设置BeanClass属性
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
// 重新创建一个RootBeanDefinition对象
mbdToUse = new RootBeanDefinition(mbd);
// 设置BeanClass属性值
mbdToUse.setBeanClass(resolvedClass);
}
其中的resolveBeanClass方法：解析Class
锁定class，根据设置的class属性或者根据className 来解析 Class
有的话，返回已经保存的beanClass；没有的话，执行doResolveBeanClass方法。
protected Class<?> resolveBeanClass(RootBeanDefinition mbd, String beanName, Class<?>... typesToMatch)
throws CannotLoadBeanClassException {
// 如果beanClass被加载了
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);
}
}
而resolveBeanClass其中的判断条件，hasBeanClass方法：
判断beanClass是不是class类，是的，就表示加载过了。没有加载的话，执行doResolveBeanClass方法
@Nullable
private volatile Object beanClass;
public boolean hasBeanClass() {
return (this.beanClass instanceof Class);
}
resolveBeanClass方法的doResolveBeanClass方法：
获取mbd配置的bean类名，将bean类名解析为Class对象,并将解析后的Class对象缓存在mdb中以备将来使用
private Class<?> doResolveBeanClass(RootBeanDefinition mbd, Class<?>... typesToMatch)
throws ClassNotFoundException {
//获取该工厂的加载bean用的类加载器
ClassLoader beanClassLoader = getBeanClassLoader();
//初始化动态类加载器为该工厂的加载bean用的类加载器,如果该工厂有
// 临时类加载器器时，该动态类加载器就是该工厂的临时类加载器
ClassLoader dynamicLoader = beanClassLoader;
boolean freshResolve = false;
//不是重点
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());
}
}
}
}
//从mbd中获取配置的bean类名
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 {
//重点
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);
}
doResolveBeanClass其中的getBeanClassLoader方法：
获取当前线程的类加载器， ClassUtils.getDefaultClassLoader在起作用
@Nullable
private ClassLoader beanClassLoader = ClassUtils.getDefaultClassLoader();
@Nullable
public ClassLoader getBeanClassLoader() {
return this.beanClassLoader;
}
ClassUtils.getDefaultClassLoader方法：获取当前线程的类加载器
@Nullable
public static ClassLoader getDefaultClassLoader() {
ClassLoader cl = null;
// 优先获取线程中的类加载器
try {
cl = Thread.currentThread().getContextClassLoader();
}
catch (Throwable ex) {
// Cannot access thread context ClassLoader - falling back...
}
// 线程中类加载器为null的情况下，获取加载ClassUtils类的类加载器
if (cl == null) {
// No thread context class loader -> use class loader of this class.
cl = ClassUtils.class.getClassLoader();
if (cl == null) {
// getClassLoader() returning null indicates the bootstrap ClassLoader
// 加入ClassUtils是被Bootstrap类加载器加载的，则获取系统类加载器
try {
cl = ClassLoader.getSystemClassLoader();
}
catch (Throwable ex) {
// Cannot access system ClassLoader - oh well, maybe the caller can live with null...
}
}
}
return cl;
}
03.这段用于 验证及准备覆盖的方法
// Prepare method overrides.
// 验证及准备覆盖的方法,lookup-method replace-method，当需要创建的bean对象中包含了lookup-method和replace-method标签的时候，会产生覆盖操作
try {
mbdToUse.prepareMethodOverrides();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
beanName, "Validation of method overrides failed", ex);
}
04.这段用于实例化前的操作
try {
// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
// 给BeanPostProcessors一个机会来返回代理来替代真正的实例，应用实例化前的前置处理器,用户自定义动态代理的方式，针对于当前的被代理类需要经过标准的代理流程来创建对象
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);
}
resolveBeforeInstantiation方法：
@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;
}
其中的hasInstantiationAwareBeanPostProcessors方法：直接判断集合是不是空
protected boolean hasInstantiationAwareBeanPostProcessors() {
return !getBeanPostProcessorCache().instantiationAware.isEmpty();
}
hasInstantiationAwareBeanPostProcessors方法的getBeanPostProcessorCache方法：
@Nullable
private volatile BeanPostProcessorCache beanPostProcessorCache;
static class BeanPostProcessorCache {
final List<InstantiationAwareBeanPostProcessor> instantiationAware = new ArrayList<>();
final List<SmartInstantiationAwareBeanPostProcessor> smartInstantiationAware = new ArrayList<>();
final List<DestructionAwareBeanPostProcessor> destructionAware = new ArrayList<>();
final List<MergedBeanDefinitionPostProcessor> mergedDefinition = new ArrayList<>();
}
BeanPostProcessorCache getBeanPostProcessorCache() {
BeanPostProcessorCache bpCache = this.beanPostProcessorCache;
if (bpCache == null) {
bpCache = new BeanPostProcessorCache();
for (BeanPostProcessor bp : this.beanPostProcessors) {
if (bp instanceof InstantiationAwareBeanPostProcessor) {
bpCache.instantiationAware.add((InstantiationAwareBeanPostProcessor) bp);
if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
bpCache.smartInstantiationAware.add((SmartInstantiationAwareBeanPostProcessor) bp);
}
}
if (bp instanceof DestructionAwareBeanPostProcessor) {
bpCache.destructionAware.add((DestructionAwareBeanPostProcessor) bp);
}
if (bp instanceof MergedBeanDefinitionPostProcessor) {
bpCache.mergedDefinition.add((MergedBeanDefinitionPostProcessor) bp);
}
}
this.beanPostProcessorCache = bpCache;
}
return bpCache;
}
举例：
InstantiationAwareBeanPostProcessor 接口：这个接口用于实例化前，bean的实例化在初始化之前
虽然和BeanPostProcessor接口中的两个方法postProcessBeforeInstantiation，postProcessAfterInstantiation重名，但是呢，参数类型不一样，是可以识别差别的。
public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {
@Nullable
default Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
return null;
}
default boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
return true;
}
@Nullable
default PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName)
throws BeansException {
return null;
}
@Deprecated
@Nullable
default PropertyValues postProcessPropertyValues(
PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException {
return pvs;
}
}
InstantiationAwareBeanPostProcessor 的实现类：
实现InstantiationAwareBeanPostProcessor 接口，不光会重写InstantiationAwareBeanPostProcessor 特有的三个方法，还会写BeanPostProcessor接口的两个方法：分别用于实例化和初始化
public class MyInstantiationAwareBeanPostProcessor implements InstantiationAwareBeanPostProcessor {
/**
* 实例化之前的操作
*/
@Override
public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
// 这里也可以返回普通对象
System.out.println("当前beanName：" + beanName + "--> 执行：postProcessBeforeInstantiation 实例化之前");
if (beanClass == MyConfig.class) {
// 创建动态代理类的增强类
Enhancer enhancer = new Enhancer();
// 设置类加载器
enhancer.setClassLoader(beanClass.getClassLoader());
// 设置被动态代理类所代理的 被代理类
enhancer.setSuperclass(beanClass);
// 设置方法拦截器
enhancer.setCallback(new QzkMethodInterceptor());
// 创建代理类
BeforeInstantiation beforeInstantiation = (BeforeInstantiation) enhancer.create();
System.out.println("创建代理对象：" + beforeInstantiation);
return beforeInstantiation;
}
return nulll;
}
/**
* 实例化之后的操作
*/
@Override
public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
// MyConfig config = (MyConfig)bean; 这里也可以调整 属性的值或者其他操作
//其实就是 相当于 经历spring的完整的对象创建过程然后调整属性的值的一个操作
config.age=10;
System.out.println("当前beanName：" + beanName + "--> 执行：postProcessAfterInstantiation 实例化之后");
return false;
}
/**
* 对当前属性值的一个相关处理工作
*/
@Override
public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) throws BeansException {
System.out.println("当前beanName：" + beanName + "--> 执行：postProcessProperties 属性值的处理");
return pvs;
}
/**
* 初始化之前的做哪些操作
*/
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
System.out.println("当前beanName：" + beanName + "--> 执行：postProcessBeforeInitialization 初始化之前");
return bean;
}
/**
* 初始化之后做哪些操作
*/
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
System.out.println("当前beanName：" + beanName + "--> 执行：postProcessAfterInitialization 初始化之后");
return bean;
}
}
resolveBeforeInstantiation方法的determineTargetType：
protected Class<?> determineTargetType(String beanName, RootBeanDefinition mbd, Class<?>... typesToMatch) {
// 判断BeanDefinition所代表的类型
// 如果BeanDefinition设置了factoryMethod，那么就是该方法的返回类型，否则就是beanClass属性所表示的类型
Class<?> targetType = mbd.getTargetType();
if (targetType == null) {
targetType = (mbd.getFactoryMethodName() != null ?
getTypeForFactoryMethod(beanName, mbd, typesToMatch) :
resolveBeanClass(mbd, beanName, typesToMatch));
if (ObjectUtils.isEmpty(typesToMatch) || getTempClassLoader() == null) {
mbd.resolvedTargetType = targetType;
}
}
return targetType;
}
applyBeanPostProcessorsBeforeInstantiation方法：
执行postProcessBeforeInstantiation方法
在bean 实例化前调用，也就是将 AbstractBeanDefinition 转换为 BeanWrapper 前的处理。给子类一个修改BeanDefinition的机会，也就是说当程序经过这个方法后，bean可能已经不是我们所认为的bean了。或许是一个经过代理的代理bean。可能是通过cglib生成的，也可能是通过其他技术生成的。
@Nullable
protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
for (InstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().instantiationAware) {
Object result = bp.postProcessBeforeInstantiation(beanClass, beanName);
if (result != null) {
return result;
}
}
return null;
}
applyBeanPostProcessorsAfterInitialization方法：这里是bean创建后的后置方法调用，逻辑基本类似。不同的是到达这一步时，Bean已经创建成功，并且注入属性也进行了赋值。
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;
}
05.实际创建bean的调用doCreateBean
try {
// 实际创建bean的调用
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);
}
06.doCreateBean方法，真正的创建方法
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
// 这个beanWrapper是用来持有创建出来的bean对象的
BeanWrapper instanceWrapper = null;
// 获取factoryBean实例缓存
if (mbd.isSingleton()) {
// 如果是单例对象，从factorybean实例缓存中移除当前bean定义信息
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
// 没有就创建实例
if (instanceWrapper == null) {
// 根据执行bean使用对应的策略创建新的实例，如，工厂方法，构造函数主动注入、简单初始化
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
// 从包装类中获取原始bean
Object bean = instanceWrapper.getWrappedInstance();
// 获取具体的bean对象的Class属性
Class<?> beanType = instanceWrapper.getWrappedClass();
// 如果不等于NullBean类型，那么修改目标类型
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
// Allow post-processors to modify the merged bean definition.
// 允许beanPostProcessor去修改合并的beanDefinition
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
// MergedBeanDefinitionPostProcessor后置处理器修改合并bean的定义
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.
// 判断当前bean是否需要提前曝光：单例&允许循环依赖&当前bean正在创建中，检测循环依赖
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");
}
// 为避免后期循环依赖，可以在bean初始化完成前将创建实例的ObjectFactory加入工厂
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
// 初始化bean实例
Object exposedObject = bean;
try {
// 对bean的属性进行填充，将各个属性值注入，其中，可能存在依赖于其他bean的属性，则会递归初始化依赖的bean
populateBean(beanName, mbd, instanceWrapper);
// 执行初始化逻辑
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) {
// 从缓存中获取具体的对象
Object earlySingletonReference = getSingleton(beanName, false);
// earlySingletonReference只有在检测到有循环依赖的情况下才会不为空
if (earlySingletonReference != null) {
// 如果exposedObject没有在初始化方法中被改变，也就是没有被增强
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) {
// 返回false说明依赖还没实例化好
if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
actualDependentBeans.add(dependentBean);
}
}
// 因为bean创建后所依赖的bean一定是已经创建的
// actualDependentBeans不为空则表示当前bean创建后其依赖的bean却没有全部创建完，也就是说存在循环依赖
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 {
// 注册bean对象，方便后续在容器销毁的时候销毁对象
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}
07.这一点：
// Instantiate the bean.
// 这个beanWrapper是用来持有创建出来的bean对象的
BeanWrapper instanceWrapper = null;
// 获取factoryBean实例缓存
if (mbd.isSingleton()) {
// 如果是单例对象，从factorybean实例缓存中移除当前bean定义信息
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
// 没有就创建实例
if (instanceWrapper == null) {
// 根据执行bean使用对应的策略创建新的实例，如，工厂方法，构造函数主动注入、简单初始化
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
isSingleton方法：
String SCOPE_SINGLETON = ConfigurableBeanFactory.SCOPE_SINGLETON;
String SCOPE_SINGLETON = "singleton";
public static final String SCOPE_DEFAULT = "";
@Override
public boolean isSingleton() {
//SCOPE_SINGLETON=“” SCOPE_DEFAULT= "singleton"
return SCOPE_SINGLETON.equals(this.scope) || SCOPE_DEFAULT.equals(this.scope);
}
createBeanInstance方法：这个以后讲，是真正创建bean的函数
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// Make sure bean class is actually resolved at this point.
// 解析bean，获取class
Class<?> beanClass = resolveBeanClass(mbd, beanName);
// beanClass != null && 当前类不是public && 不允许访问非公共构造函数和方法。抛出异常
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());
}
// 1. 是否有bean的 Supplier 接口，如果有，通过回调来创建bean
Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
if (instanceSupplier != null) {
return obtainFromSupplier(instanceSupplier, beanName);
}
// 2. 如果工厂方法不为空，则使用工厂方法初始化策略
// 通过 @Bean 注解方法注入的bean 或者xml 配置注入 的BeanDefinition 会存在这个值。而注入这个bean的方法就是工厂方法。后面会详细解读
if (mbd.getFactoryMethodName() != null) {
// 执行工厂方法，创建bean
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
// Shortcut when re-creating the same bean...
// 3. 尝试使用构造函数构建bean，后面详解
// 经过上面两步，Spring确定没有其他方式来创建bean，所以打算使用构造函数来进行创建bean。 但是 bean 的构造函数可能有多个，需要确定使用哪一个。
// 这里实际上是一个缓存，resolved 表示构造函数是否已经解析完成；autowireNecessary 表示是否需要自动装配
boolean resolved = false;
boolean autowireNecessary = false;
if (args == null) {
synchronized (mbd.constructorArgumentLock) {
// 一个类可能有多个不同的构造函数，每个构造函数参数列表不同，所以调用前需要根据参数锁定对应的构造函数或工程方法
// 如果这个bean的构造函数或者工厂方法已经解析过了，会保存到 mbd.resolvedConstructorOrFactoryMethod 中。这里来判断是否已经解析过了。
if (mbd.resolvedConstructorOrFactoryMethod != null) {
resolved = true;
autowireNecessary = mbd.constructorArgumentsResolved;
}
}
}
// 如果已经解析过则使用功能解析好的构造函数方法，不需要再次解析。这里的是通过 mbd.resolvedConstructorOrFactoryMethod 属性来缓存解析过的构造函数。
if (resolved) {
if (autowireNecessary) {
// 4. 构造函数自动注入
return autowireConstructor(beanName, mbd, null, null);
}
else {
// 5. 使用默认构造函数构造
return instantiateBean(beanName, mbd);
}
}
// Candidate constructors for autowiring?
// 6. 根据参数解析构造函数，并将解析出来的构造函数缓存到mdb 的 resolvedConstructorOrFactoryMethod 属性中
// 到这一步，说明 bean 是第一次加载，所以没有对构造函数进行相关缓存(resolved 为 false)
// 调用 determineConstructorsFromBeanPostProcessors 方法来获取指定的构造函数列表。后面详解
Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
return autowireConstructor(beanName, mbd, ctors, args);
}
// Preferred constructors for default construction?
// 获取最优的构造函数
ctors = mbd.getPreferredConstructors();
if (ctors != null) {
// 构造函数自动注入
return autowireConstructor(beanName, mbd, ctors, null);
}
// No special handling: simply use no-arg constructor.
// 使用默认构造函数构造
return instantiateBean(beanName, mbd);
}
08.
// 从包装类中获取原始bean
Object bean = instanceWrapper.getWrappedInstance();
// 获取具体的bean对象的Class属性
Class<?> beanType = instanceWrapper.getWrappedClass();
// 如果不等于NullBean类型，那么修改目标类型
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
09.和beanDefinition操作和@Auotwired注解有关
// Allow post-processors to modify the merged bean definition.
// 允许beanPostProcessor去修改合并的beanDefinition
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
// MergedBeanDefinitionPostProcessor后置处理器修改合并bean的定义
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}
10.循环依赖
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");
}
// 为避免后期循环依赖，可以在bean初始化完成前将创建实例的ObjectFactory加入工厂
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
11.属性填充和初始化
// Initialize the bean instance.
// 初始化bean实例
Object exposedObject = bean;
try {
// 对bean的属性进行填充，将各个属性值注入，其中，可能存在依赖于其他bean的属性，则会递归初始化依赖的bean
populateBean(beanName, mbd, instanceWrapper);
// 执行初始化逻辑
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);
}
}
顺序：
