Spring扩展点之FactoryBean接口

旧城等待， 2024-04-19 13:03 15阅读 0赞

#### 首先看一下接口定义    ####

由接口定义可以看出来，实现这个接口的bean不是主要功能，`getObject()`创建的对象才是重点。那么在这我们就可以猜到了，可以是使用`FactoryBean`创建一些实例化过程比较复杂的bean

#### `FactoryBean`的注册 ####

`FactoryBean`的处理逻辑在`AbstractBeanFactory.doGetBean`方法内

看一下具体的逻辑，这里需要注意Spring关于bean的name有个潜规则，凡是以&开头的bean名称都默认为`FactoryBean`

<table> 
 <tbody> 
 <tr> 
 <td><pre>1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 </pre></td> 
 <td><pre> protected Object getObjectForBeanInstance( Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {
 	 // 如果beanName以工厂引用&amp;开头 if (BeanFactoryUtils.isFactoryDereference(name)) {
 if (beanInstance instanceof NullBean) {
 return beanInstance; } // 如果name以&amp;开头，而beanInstance不是FactoryBean类型，则抛异常 if (!(beanInstance instanceof FactoryBean)) {
 throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass()); } } // 如果beanInstance不是FactoryBean类型，则直接返回beanInstance // 或者name以&amp;开头，也直接返回beanInstance，说明我们就想获取FactoryBean实例 if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
 return beanInstance; } Object object = null; if (mbd == null) {
 object = getCachedObjectForFactoryBean(beanName); } if (object == null) {
 // 此时beanInstance是FactoryBean类型，而name又不是以&amp;开头; 这是我们示例工程的情况，也是最普通、用的最多的情况 // 将beanInstance强转成FactoryBean类型 FactoryBean&lt;?&gt; factory = (FactoryBean&lt;?&gt;) beanInstance; // 从缓存中获取我们需要的实例对象 if (mbd == null &amp;&amp; containsBeanDefinition(beanName)) {
 mbd = getMergedLocalBeanDefinition(beanName); } boolean synthetic = (mbd != null &amp;&amp; mbd.isSynthetic()); // 调用FactoryBean的getObject方法创建我们需要的实例对象 object = getObjectFromFactoryBean(factory, beanName, !synthetic); } return object; } protected Object getObjectFromFactoryBean(FactoryBean&lt;?&gt; factory, String beanName, boolean shouldPostProcess) {
 //针对单例的处理 if (factory.isSingleton() &amp;&amp; containsSingleton(beanName)) {
 synchronized (getSingletonMutex()) {
 Object object = this.factoryBeanObjectCache.get(beanName); if (object == null) {
 //通过factory.getObject获取 object = doGetObjectFromFactoryBean(factory, beanName); 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); } } if (containsSingleton(beanName)) {
 //将获取到的对象放到factoryBeanObjectCache单例缓存map进行存储 this.factoryBeanObjectCache.put(beanName, object); } } } return object; } } else {
 //非单例的处理，直接通过factory.getObejct获取，然后再返回给用户 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; } } </pre></td> 
 </tr> 
 </tbody> 
</table>

生成bean对象的方法：

#### Spring的实现 ####

Spring中实现这个接口的bean有很多，但是我们最熟悉也是最重要的就是在我之前文章中提到过得`ProxyFactoryBean`这个bean是实现AOP技术的重点，简单回顾一下

![640?wx\_fmt=png][640_wx_fmt_png]

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