前言
本章开始分析finishBeanFactoryInitialization(beanFactory)方法，直译过来就是完成Bean工厂的初始化，这中间就是非lazy单例Bean的实例化流程。ConversionService在第十章已经提前分析了。重点就是最后一句，我们的bean实例化分析就从这里开始。
本章主要是实例化流程的分析，不会太深入到细节
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// Initialize conversion service for this context.
// ConversionService（转换服务）在spring框架中用于处理类型转换的任务。它提供了一种统一的方式来执行各种类型之间的转换操作，
// 包括字符串到其他类型的转换、日期和时间的转换、数字类型的转换等。
if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
beanFactory.setConversionService(
beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
}
// Register a default embedded value resolver if no BeanFactoryPostProcessor
// (such as a PropertySourcesPlaceholderConfigurer bean) registered any before:
// at this point, primarily for resolution in annotation attribute values.
if (!beanFactory.hasEmbeddedValueResolver()) {
beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
}
// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}
// Stop using the temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(null);
// Allow for caching all bean definition metadata, not expecting further changes.
beanFactory.freezeConfiguration();
// Instantiate all remaining (non-lazy-init) singletons.
beanFactory.preInstantiateSingletons();
}
预处理单例bean
preInstantiateSingletons() 是 Spring 容器的一个方法，它用于预实例化所有的单例（Singleton）Bean。
@Override
public void preInstantiateSingletons() throws BeansException {
if (logger.isTraceEnabled()) {
logger.trace("Pre-instantiating singletons in " + this);
}
// Iterate over a copy to allow for init methods which in turn register new bean definitions.
// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
for (String beanName : beanNames) {
// 通过bean的名称去获取bean的定义信息
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
// 不是抽象类&&是单例的&&不是懒加载
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
if (isFactoryBean(beanName)) {
Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
if (bean instanceof FactoryBean) {
FactoryBean<?> factory = (FactoryBean<?>) bean;
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged(
(PrivilegedAction<Boolean>) ((SmartFactoryBean<?>) factory)::isEagerInit,
getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
}
else {
getBean(beanName);
}
}
}
// Trigger post-initialization callback for all applicable beans...
for (String beanName : beanNames) {
Object singletonInstance = getSingleton(beanName);
if (singletonInstance instanceof SmartInitializingSingleton) {
StartupStep smartInitialize = this.getApplicationStartup().start("spring.beans.smart-initialize")
.tag("beanName", beanName);
SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
smartSingleton.afterSingletonsInstantiated();
return null;
}, getAccessControlContext());
}
else {
smartSingleton.afterSingletonsInstantiated();
}
smartInitialize.end();
}
}
}
这个预处理单例bean的实例化其实非常简单，我们简要分析一下整体流程：
- 获取到当前所有的beanDefinitionNames，用于迭代。
- 循环所有的beanDefinitionNames，也就是beanNamess
- 获取beanName的定义信息，用于后续判断
- 如果是抽象类，或者不是单例或者是懒加载bean就不处理。
- 其他情况下会进入getBean逻辑，这个方法我们经常用来从 BeanFactory 中获取一个 Bean，而初始化的过程也封装到了这个方法里。
getBean/doGetBean
Spring源码中很多时候真正做事的是do开头的，个人经验。
@Override
public Object getBean(String name) throws BeansException {
return doGetBean(name, null, null, false);
}
transformedBeanName
获取beanName，如果是FactoryBean是会以&开头，也就是说这里返回的就是单纯的beanName
String beanName = transformedBeanName(name);
public static String transformedBeanName(String name) {
Assert.notNull(name, "'name' must not be null");
if (!name.startsWith(BeanFactory.FACTORY_BEAN_PREFIX)) {
return name;
}
return transformedBeanNameCache.computeIfAbsent(name, beanName -> {
do {
beanName = beanName.substring(BeanFactory.FACTORY_BEAN_PREFIX.length());
}
while (beanName.startsWith(BeanFactory.FACTORY_BEAN_PREFIX));
return beanName;
});
}
getSingleton
这里就是常说的三级缓存。在实例化的时候先要去三级缓存中查看是否存在了，需不需要走后续的实例化流程。
Object sharedInstance = getSingleton(beanName);
@Nullable
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
// Quick check for existing instance without full singleton lock
Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null && allowEarlyReference) {
synchronized (this.singletonObjects) {
// Consistent creation of early reference within full singleton lock
singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null) {
ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
if (singletonFactory != null) {
singletonObject = singletonFactory.getObject();
this.earlySingletonObjects.put(beanName, singletonObject);
this.singletonFactories.remove(beanName);
}
}
}
}
}
}
return singletonObject;
}
从上述代码中，我们知道有三个Map对象，也就是我们常说的三级缓存，实际上就是以下这三个Map。
/** Cache of singleton objects: bean name to bean instance. */
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);
/** Cache of singleton factories: bean name to ObjectFactory. */
private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<>(16);
/** Cache of early singleton objects: bean name to bean instance. */
private final Map<String, Object> earlySingletonObjects = new ConcurrentHashMap<>(16);
- 一级缓存：singletonObjects缓存的是单例对象，key是beanName value是bean的实例。
- 二级缓存：earlySingletonObjects缓存的是早期的单例对象，key是beanName value是bean的实例。
- 三级缓存：singletonFactories缓存的是ObjectFactory，key是beanName value是ObjectFactory。
回到getSingleton方法，首先spring尝试通过beanName从一级缓存中获取，如果一级缓存中不存在，并且当前bean并不是正在创建中的话直接返回null。只有当bean正在创建中的时候才回去从二级缓存中获取，如果二级缓存中获取不到再从三级缓存中去获取。此处我们先大概有这么一个概念，后续会在循环依赖章节详细描述。
如果当前获取到的sharedInstance不为空且不是FacotyBean的话就直接返回回去了。如果为空继续走后续的逻辑。
dependsOn
根据BeanDefinition获取是否有依赖的bean，如果有的话先把其他bean实例化完成。@DependsOn的注解的作用就在这里可以体现。
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);
try {
getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
}
}
}
singletonsCurrentlyInCreation
如果是单例的，就会调用 getSingleton(String beanName, ObjectFactory<?> singletonFactory)方法。
- 第一个参数就是beanName
- 第二个参数是一个FunctionalInterface
if (mbd.isSingleton()) {
// 先执行getSingleton方法，然后在代码中会调用createBean方法
sharedInstance = getSingleton(beanName, () -> {
try {
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
destroySingleton(beanName);
throw ex;
}
});
beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
执行getSingleton方法，代码如下
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(beanName, "Bean name must not be null");
synchronized (this.singletonObjects) {
Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
if (this.singletonsCurrentlyInDestruction) {
throw new BeanCreationNotAllowedException(beanName,
"Singleton bean creation not allowed while singletons of this factory are in destruction " +
"(Do not request a bean from a BeanFactory in a destroy method implementation!)");
}
if (logger.isDebugEnabled()) {
logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
}
// 对象是否正在创建中 singletonsCurrentlyInCreation，避免循环依赖的一种操作
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {
this.suppressedExceptions = new LinkedHashSet<>();
}
try {
// 在这里调用外出的createBean返回的就是springbean，然后后续执行缓存的相关操作
singletonObject = singletonFactory.getObject();
newSingleton = true;
}
catch (IllegalStateException ex) {
// Has the singleton object implicitly appeared in the meantime ->
// if yes, proceed with it since the exception indicates that state.
singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
throw ex;
}
}
catch (BeanCreationException ex) {
if (recordSuppressedExceptions) {
for (Exception suppressedException : this.suppressedExceptions) {
ex.addRelatedCause(suppressedException);
}
}
throw ex;
}
finally {
if (recordSuppressedExceptions) {
this.suppressedExceptions = null;
}
afterSingletonCreation(beanName);
}
if (newSingleton) {
addSingleton(beanName, singletonObject);
}
}
return singletonObject;
}
}
首先这个放回加了一个synchronized的锁，锁的是一级缓存对象，也就是说对象的实例化是线程安全的，不让其在实例化的时候出现重复创建。获取锁之后会再从缓存中去获取当前beanName是否存在实例，如果没有的话会执行beforeSingletonCreation(beanName)。
protected void beforeSingletonCreation(String beanName) {
if (!this.inCreationCheckExclusions.contains(beanName) && !this.singletonsCurrentlyInCreation.add(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
}
此处的核心就是singletonsCurrentlyInCreation集合的add方法，就是提前曝光的地方。
private final Set<String> singletonsCurrentlyInCreation =
Collections.newSetFromMap(new ConcurrentHashMap<>(16));
直接就是会调用传入的FunctionalInterface，也就是执行createBean方法。
try {
// 在这里调用外出的createBean返回的就是springbean，然后后续执行缓存的相关操作
singletonObject = singletonFactory.getObject();
newSingleton = true;
}
createBean/doCreateBean
在执行doCreateBean的时候会调用构造方法
if (instanceWrapper == null) {
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
然后判断beanDefinition信息是单例的，并且是允许循环依赖的（默认为允许）并且当前的bean是正在创建中就会进入if的逻辑。
addSingletonFactory,从名字开发猜测是否和我们的三级缓存有关联。
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");
}
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
addSingletonFactory方法的参数如下：
- beanName，bean的名称
- ObjectFactory，函数式接口，之前看getSingleton(name)方法的时候也知道，会调用这个getObject方法来获取对象放入二级缓存中。
一级缓存中不存在就将这个ObjectFactory放入三级缓存，同时清理掉二级缓存和加入已注册的有序集合中。
protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(singletonFactory, "Singleton factory must not be null");
synchronized (this.singletonObjects) {
if (!this.singletonObjects.containsKey(beanName)) {
this.singletonFactories.put(beanName, singletonFactory);
this.earlySingletonObjects.remove(beanName);
this.registeredSingletons.add(beanName);
}
}
}
populateBean
填充bean，也就是属性注入。这里会去解析bean的依赖，从而继续去走getBean的逻辑来让当前bean实例化完整。
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 {
// property mean 属性
// Skip property population phase for null instance.
return;
}
}
// Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
// state of the bean before properties are set. This can be used, for example,
// to support styles of field injection.
// 在属性填充之前给任意InstantiationAwareBeanPostProcessors一个机会去修改bean的状态
// 后置处理器可以被使用在例如:支持字段注入的样式.
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
for (InstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().instantiationAware) {
if (!bp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
return;
}
}
}
PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);
int resolvedAutowireMode = mbd.getResolvedAutowireMode();
if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
// Add property values based on autowire by name if applicable.
if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {
autowireByName(beanName, mbd, bw, newPvs);
}
// Add property values based on autowire by type if applicable.
if (resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
autowireByType(beanName, mbd, bw, newPvs);
}
pvs = newPvs;
}
boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);
PropertyDescriptor[] filteredPds = null;
if (hasInstAwareBpps) {
if (pvs == null) {
pvs = mbd.getPropertyValues();
}
// 实例化感知的BeanPostProcessor
for (InstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().instantiationAware) {
// 默认的情况下resolvedAutowireMode是为0的，所以默认是AutoWiredAnnotationBeanPostProcessor进行自动装配
PropertyValues pvsToUse = bp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
// 在这里面回去校验属性的版本信息（BeanNotOfRequiredTypeException）
/**
*Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException:
* Error creating bean with name 'b': Unsatisfied dependency expressed through field 'a';
* nested exception is org.springframework.beans.factory.BeanNotOfRequiredTypeException:
* Bean named 'a' is expected to be of type 'com.qhyu.cloud.circlarRefrence.A' but was actually of type 'com.sun.proxy.$Proxy34'
*/
pvsToUse = bp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
return;
}
}
pvs = pvsToUse;
}
}
if (needsDepCheck) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
checkDependencies(beanName, mbd, filteredPds, pvs);
}
if (pvs != null) {
// 属性填充的最后回对spel进行解析
applyPropertyValues(beanName, mbd, bw, pvs);
}
}
initializeBean
如果 bean 实现了 BeanNameAware、BeanClassLoaderAware 或 BeanFactoryAware 接口，回调invokeAwareMethods(beanName, bean)
处理 bean 中定义的 init-method，或者如果 bean 实现了 InitializingBean 接口，调用 afterPropertiesSet() 方法
protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
}
else {
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
// 先执行beanpostProcessor的before
// 通过BeanPostProcessor在bean初始化之前做点事情
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
// 再执行initmethods
// 调用bean的初始化方法进行初始化
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
if (mbd == null || !mbd.isSynthetic()) {
// 再执行BeanPostProcessor的After方法
// 通过BeanPostProcessor在bean初始化之后做点事情
// aop的切入点
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
getSingleton
如果创建没有任何问题，newSingleton = true，继续执行 addSingleton(beanName, singletonObject)方法
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(beanName, "Bean name must not be null");
synchronized (this.singletonObjects) {
Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
if (this.singletonsCurrentlyInDestruction) {
throw new BeanCreationNotAllowedException(beanName,
"Singleton bean creation not allowed while singletons of this factory are in destruction " +
"(Do not request a bean from a BeanFactory in a destroy method implementation!)");
}
if (logger.isDebugEnabled()) {
logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
}
// 对象是否正在创建中 singletonsCurrentlyInCreation，避免循环依赖的一种操作
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {
this.suppressedExceptions = new LinkedHashSet<>();
}
try {
// 在这里调用外出的createBean返回的就是springbean，然后后续执行缓存的相关操作
singletonObject = singletonFactory.getObject();
newSingleton = true;
}
catch (IllegalStateException ex) {
// Has the singleton object implicitly appeared in the meantime ->
// if yes, proceed with it since the exception indicates that state.
singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
throw ex;
}
}
catch (BeanCreationException ex) {
if (recordSuppressedExceptions) {
for (Exception suppressedException : this.suppressedExceptions) {
ex.addRelatedCause(suppressedException);
}
}
throw ex;
}
finally {
if (recordSuppressedExceptions) {
this.suppressedExceptions = null;
}
afterSingletonCreation(beanName);
}
if (newSingleton) {
addSingleton(beanName, singletonObject);
}
}
return singletonObject;
}
}
将创建好的bean放入一级缓存，移除一二级缓存。
protected void addSingleton(String beanName, Object singletonObject) {
// 线程安全的
synchronized (this.singletonObjects) {
// 放入一级缓存
this.singletonObjects.put(beanName, singletonObject);
// 移除三级缓存
this.singletonFactories.remove(beanName);
// 移除二级缓存
this.earlySingletonObjects.remove(beanName);
// 已注册的map中把新初始化的bean放入
this.registeredSingletons.add(beanName);
}
}
总结
整个bean的初始化流程就如下图所示，下面的这个图是一个最简单的单例bean的实例化流程，不涉及到循环依赖问题，循环依赖和三级缓存将在下一章详细分析。本章主要了解bean实例化的整体流程，了解和熟悉spring工作模式。
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