一次性讲清楚spring中bean的生命周期之二：FactoryBean的前世今生

2401_84103616

于 2024-04-10 04:22:28 发布

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分类专栏： 2024年程序员学习文章标签： spring java 后端

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RootBeanDefintion mbd BeanDefinition

看下面的表格更容易理解该方法在各种情况下的返回值，

beanInstance	name	返回值
FactoryBean的实例	带有&	beanInstance
不是FactoryBean的实例	带有&	beanInstance
FactoryBean的实例	不带&	beanInstance生产的对象
不是FactoryBean的实例	不带&	beanInstance

通过上面得表格再结合代码就很容易理解，只要是返回beanInstance对象，那么就是FactroyBean的前世，下面看FactoryBean的今生。

今生

–

这里有两个方法需要分析，分别是getCachedObjectForFactoryBean和getObjectFromFactoryBean。第一个方法是从缓存中获取，也就是说使用FactoryBean生产的bean会单独放在缓存中，非singletonObjects中，这点务必要注意。

getCachedObjectForFactoryBean

先看下该方法的定义，

@Nullable

protected Object getCachedObjectForFactoryBean(String beanName) {

return this.factoryBeanObjectCache.get(beanName);

}

可以看到很简单就是通过名称从factoryBeanObjectCache中取对象。factoryBeanObjectCache肯定是个map了

/** Cache of singleton objects created by FactoryBeans: FactoryBean name to object. */

private final Map<String, Object> factoryBeanObjectCache = new ConcurrentHashMap<>(16);

getObjectFromFactoryBean

复制代码

protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) {

if (factory.isSingleton() && containsSingleton(beanName)) {

synchronized (getSingletonMutex()) {

Object object = this.factoryBeanObjectCache.get(beanName);

if (object == null) {

object = doGetObjectFromFactoryBean(factory, beanName);

// Only post-process and store if not put there already during getObject() call above

// (e.g. because of circular reference processing triggered by custom getBean calls)

Object alreadyThere = this.factoryBeanObjectCache.get(beanName);

if (alreadyThere != null) {

object = alreadyThere;

}

else {

if (shouldPostProcess) {

if (isSingletonCurrentlyInCreation(beanName)) {

// Temporarily return non-post-processed object, not storing it yet…

return object;

}

beforeSingletonCreation(beanName);

try {

object = postProcessObjectFromFactoryBean(object, beanName);

}

catch (Throwable ex) {

throw new BeanCreationException(beanName,

“Post-processing of FactoryBean’s singleton object failed”, ex);

}

finally {

afterSingletonCreation(beanName);

}

//把生产的实例对象放到factoryBeanObjectCache缓存中

if (containsSingleton(beanName)) {

this.factoryBeanObjectCache.put(beanName, object);

}

return object;

}

else {

//调用getObject方法

Object object = doGetObjectFromFactoryBean(factory, beanName);

if (shouldPostProcess) {

try {

object = postProcessObjectFromFactoryBean(object, beanName);

}

catch (Throwable ex) {

throw new BeanCreationException(beanName, “Post-processing of FactoryBean’s object failed”, ex);

}

return object;

}

复制代码

该方法就比较复杂了，主要有doGetObjectFromFactoryBean、beforeSingletonCreation、postProcessObjectFromFactoryBean、afterSingletonCreation方法，重要的一个是doGetFromFactroyBean，也就是真正干活生产bean的方法。其定义如下，其余方法可自行查看

复制代码

private Object doGetObjectFromFactoryBean(final FactoryBean<?> factory, final String beanName)

throws BeanCreationException {

Object object;

try {

if (System.getSecurityManager() != null) {

AccessControlContext acc = getAccessControlContext();

try {

object = AccessController.doPrivileged((PrivilegedExceptionAction) factory::getObject, acc);

}

catch (PrivilegedActionException pae) {

throw pae.getException();