BeanFactory
簡介
BeanFactory是Spring容器的Root Interface,提供了 IOC 容器最基本的功能。
BeanFactory只是一個接口,沒有具體的實現,但是它的實現類如XmlBeanFactory,ApplicationContext在其基礎之上附加了其他的功能。
源碼
public interface BeanFactory {
/**
*
*/
String FACTORY_BEAN_PREFIX = "&";
/**
* 這個方法是BeanFactory的主要方法,通過指定名字可以取得IOC容器中相應的Bean對象
* 這種方法使得Spring BeanFactory代替單例或原型設計模式來獲取Bean對象
*/
Object getBean(String name) throws BeansException;
/**
* 也是獲取Bean對象的方法,但是增加了Class類型的安全驗證機制
* 如果類型不符,則跑出BeanNotOfRequiredTypeException異常
*/
<T> T getBean(String name, Class<T> requiredType) throws BeansException;
/**
* 通過Bean類型獲取bean實例
*/
<T> T getBean(Class<T> requiredType) throws BeansException;
/**
* 傳入的參數什麼用途 暫時不清楚
*/
Object getBean(String name, Object... args) throws BeansException;
/**
*
*/
<T> T getBean(Class<T> requiredType, Object... args) throws BeansException;
/**
* 判斷是否含有指定名字的bean對象
*/
boolean containsBean(String name);
/**
*判斷指定名稱的bean對象是否是單例,如果是,則永遠返回同一個對象
* 可以在 BeanDefinition中設置
*/
boolean isSingleton(String name) throws NoSuchBeanDefinitionException;
/**
* 判斷Bean是不是prototype的bean,是的話 返回獨立的實例
*/
boolean isPrototype(String name) throws NoSuchBeanDefinitionException;
/**
*
*/
boolean isTypeMatch(String name, ResolvableType typeToMatch) throws NoSuchBeanDefinitionException;
/**
* 判斷指定名稱的bean對象的Class類型是否是特定的Class類型。
*/
boolean isTypeMatch(String name, Class<?> typeToMatch) throws NoSuchBeanDefinitionException;
/**
* 獲取指定名稱bean對象的Class類型
*/
Class<?> getType(String name) throws NoSuchBeanDefinitionException;
/**
*查詢指定了名字的bean的所有別名,這些別名都是在BeanDefinition中定義的
*/
String[] getAliases(String name);
}
FactoryBean
簡介
FactoryBean是一個接口,當在IOC容器中的Bean實現了FactoryBean後,通過getBean(String BeanName)獲取到的Bean對象並不是FactoryBean的實現類對象,而是這個實現類中的getObject()方法返回的對象。如果要獲取FactoryBean對象,在beanName前面加一個&符號來獲取,如:getBean(&BeanName)。
源碼
getBean
protected <T> T doGetBean(
final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
throws BeansException {
final String beanName = transformedBeanName(name);
Object bean;
// Eagerly check singleton cache for manually registered singletons.
Object sharedInstance = getSingleton(beanName);
if (sharedInstance != null && args == null) {
//。。。。
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
// 。。。。。
if (mbd.isSingleton()) {
//。。。。。
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
else if (mbd.isPrototype()) {
// 。。。。
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else {
//scope獲取Bean。。。。
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
}
// ......
return (T) bean;
}
我們在獲取Bean的過程中會發現,不管是從單例緩存還是新創建Bean過程中單例、原型或者Scope獲取Bean之後都會調用getObjectForBeanInstance()方法。
getObjectForBeanInstance
protected Object getObjectForBeanInstance(
Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {
// 要獲取的Bean是帶有&符號,並且beanInstance不是FactoryBean則拋出異常
if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
}
// beanInstance不是FactoryBean或者要獲取的Bean不帶有&符號,直接返回beanInstance
if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
return beanInstance;
}
Object object = null;
if (mbd == null) {
//嘗試從FactoryBean的緩存中獲取
object = getCachedObjectForFactoryBean(beanName);
}
if (object == null) {
// Return bean instance from factory.
FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
// Caches object obtained from FactoryBean if it is a singleton.
if (mbd == null && containsBeanDefinition(beanName)) {
mbd = getMergedLocalBeanDefinition(beanName);
}
boolean synthetic = (mbd != null && mbd.isSynthetic());
//通過FactoryBean#getObject()方法獲取Bean對象
object = getObjectFromFactoryBean(factory, beanName, !synthetic);
}
return object;
}
getObjectFromFactoryBean
protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) {
//判斷單例 以便加鎖、緩存
if (factory.isSingleton() && containsSingleton(beanName)) {
synchronized (getSingletonMutex()) {
Object object = this.factoryBeanObjectCache.get(beanName);
if (object == null) {
//實際調用getObject方法的地方
object = doGetObjectFromFactoryBean(factory, beanName);
Object alreadyThere = this.factoryBeanObjectCache.get(beanName);
if (alreadyThere != null) {
object = alreadyThere;
}
else {
if (object != null && shouldPostProcess) {
try {
object = postProcessObjectFromFactoryBean(object, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(beanName,
"Post-processing of FactoryBean's singleton object failed", ex);
}
}
this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT));
}
}
return (object != NULL_OBJECT ? object : null);
}
}
else {
Object object = doGetObjectFromFactoryBean(factory, beanName);
if (object != null && shouldPostProcess) {
try {
object = postProcessObjectFromFactoryBean(object, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "Post-processing of FactoryBean's object failed", ex);
}
}
return object;
}
}
應用
Spring的Aop的工廠ProxyFactoryBean就是一個FactoryBean,具體可以參考Sring源碼分析——AOP
總結
除了名字很相似外,其他沒有任何可比性,只要充分了解彼此間的特性,就不會有任何混淆了。