在AbstractBeanFactory中doGetBean對加載bean的不同情況進行拆分處理,並做了部分准備工作
具體如下
AbstractBeanFactory
@Override
public Object getBean(String name) throws BeansException {
return doGetBean(name, null, null, false);
}
protected <T> T doGetBean(
final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
throws BeansException {
// 獲取原始的bean name,去除&,解決alias問題
final String beanName = transformedBeanName(name);
Object bean;
// 嘗試從緩存中獲取bean
// Eagerly check singleton cache for manually registered singletons.
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {
if (logger.isDebugEnabled()) {
if (isSingletonCurrentlyInCreation(beanName)) {
// ...
}
else {
logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
}
}
// 如果從緩存中或得bean,還需要判斷是否是FactoryBean,並調用getObejct
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
// 如果是原型scope,這邊又是正在創建,說明有循環依賴,而原型的循環依賴Spring是不解決的
// Fail if we're already creating this bean instance:
// We're assumably within a circular reference.
if (isPrototypeCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
// 如果當前容器沒有配置bean,那麼去父容器查找
// 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 (args != null) {
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
}
// 如果不是類型檢查,這邊需要標記類正在創建
if (!typeCheckOnly) {
markBeanAsCreated(beanName);
}
try {
// 實例化類之前,先去容器中獲取配置的bean信息,這邊需要將之前的GenericBeanDefinition轉化為RootBeanDefinition
// 同時如果父bean的話,需要合並到子bean
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {
for (String dependsOnBean : dependsOn) {
if (isDependent(beanName, dependsOnBean)) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between '" + beanName + "' and '" + dependsOnBean + "'");
}
// 解決依賴
registerDependentBean(dependsOnBean, beanName);
getBean(dependsOnBean);
}
}
// 創建單例的實例
// Create bean instance
if (mbd.isSingleton()) {
// 單例情況下,為解決循環依賴,在實例化之前,先新建一個ObjectFactory實例
sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
try {
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);
}
// 創建原型實例
else if (mbd.isPrototype()) {
// It's a prototype -> create a new instance.
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
// 創建其他scope的實例
else {
String scopeName = mbd.getScope();
final Scope scope = this.scopes.get(scopeName);
if (scope == null) {
throw new IllegalStateException("No Scope registered for scope '" + scopeName + "'");
}
try {
// 還是先創建ObejctFactory,只是這邊沒有處理
Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
@Override
public Object getObject() throws BeansException {
beforePrototypeCreation(beanName);
try {
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;
}
}
// 這邊需要對實例進行類型校驗,如果與requiredType不一致,需要委托TypeConverter嘗試類型轉換
// Check if required type matches the type of the actual bean instance.
if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
try {
return getTypeConverter().convertIfNecessary(bean, requiredType);
}
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;
}上面提到在加載bean的時候,doGetBean首先嘗試的是從緩存讀取,這邊我們來細細分析下緩存具體是如何處理的.
這邊邏輯是定義在DefaultSingletonBeanRegistry中,它是AbstractBeanFactory的父類,主要職責是共享實例的注冊.
這邊雖然定義的是singleton,但是實際使用的時候,處理prototype,其他scope均使用了這邊進行緩存.
這邊主要是需要理解singletonObjects,singletonFactories,earlySingletonObjects,registeredSingletons這4個變量.
Cache of singleton objects: bean name --> bean instance
這邊緩存的是實例
Cache of singleton factories: bean name --> ObjectFactory
這邊緩存的是為解決循環依賴而准備的ObjectFactory
Cache of early singleton objects: bean name --> bean instance
這邊緩存的也是實例,只是這邊的是為解決循環依賴而提早暴露出來的實例,其實是ObjectFactory
Set of registered singletons, containing the bean names in registration order
上面三個變量,任意一個添加了,這邊都會添加bean name,標記已經注冊
我們從下面幾個方法,可以清楚看懂上面4個變量的使用:
DefaultSingletonBeanRegistry
/** * 添加實例化的bean * Add the given singleton object to the singleton cache of this factory. * <p>To be called for eager registration of singletons. * @param beanName the name of the bean * @param singletonObject the singleton object */
protectedvoidaddSingleton(String beanName, Object singletonObject) {
synchronized (this.singletonObjects) {
this.singletonObjects.put(beanName, (singletonObject != null ? singletonObject : NULL_OBJECT));
this.singletonFactories.remove(beanName);
this.earlySingletonObjects.remove(beanName);
this.registeredSingletons.add(beanName);
}
}
/** * 為解決單例的循環依賴,這邊注冊ObjectFactory * Add the given singleton factory for building the specified singleton * if necessary. * <p>To be called for eager registration of singletons, e.g. to be able to * resolve circular references. * @param beanName the name of the bean * @param singletonFactory the factory for the singleton object */
protectedvoidaddSingletonFactory(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);
}
}
}
/** * 清除實例 * Remove the bean with the given name from the singleton cache of this factory, * to be able to clean up eager registration of a singleton if creation failed. * @param beanName the name of the bean * @see #getSingletonMutex() */
protectedvoidremoveSingleton(String beanName) {
synchronized (this.singletonObjects) {
this.singletonObjects.remove(beanName);
this.singletonFactories.remove(beanName);
this.earlySingletonObjects.remove(beanName);
this.registeredSingletons.remove(beanName);
}
}
/** * 獲取實例時,調用ObejctFactory的getObject 獲取實例 * Return the (raw) singleton object registered under the given name. * <p>Checks already instantiated singletons and also allows for an early * reference to a currently created singleton (resolving a circular reference). * @param beanName the name of the bean to look for * @param allowEarlyReference whether early references should be created or not * @return the registered singleton object, or {@code null} if none found */
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
synchronized (this.singletonObjects) {
singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null && allowEarlyReference) {
ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
if (singletonFactory != null) {
singletonObject = singletonFactory.getObject();
this.earlySingletonObjects.put(beanName, singletonObject);
this.singletonFactories.remove(beanName);
}
}
}
}
return (singletonObject != NULL_OBJECT ? singletonObject : null);
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