spring各种接口的作用FactoryBean、ApplicationContextAware、InitializingBean

FactoryBean

当配置文件中<bean>的class属性配置的实现类是FactoryBean时，通过 BeanFactory#getBean()方法返回的不是FactoryBean本身，而是FactoryBean#getObject()方法所返回的对象，相当于FactoryBean#getObject()代理了getBean()方法

public interface FactoryBean<T> {
	/**
	 * Return an instance (possibly shared or independent) of the object
	 * managed by this factory.
	 */
	T getObject() throws Exception;
	Class<?> getObjectType();
	boolean isSingleton();
}

ApplicationContextAware

实现ApplicationContextAware的bean，会在Bean初始化的时候自动调用setApplicationContext，然后就可以获取spring的上下文，通过spring的上下文就可以获取到spring的一些信息，还可以获取其他的bean

public interface ApplicationContextAware extends Aware {
	/**
	 * Set the ApplicationContext that this object runs in.
	 * Normally this call will be used to initialize the object.
	 */
	void setApplicationContext(ApplicationContext applicationContext) throws BeansException;
}

InitializingBean

实现InitializingBean，在bean初始化之前会调用afterPropertiesSet()

public interface InitializingBean {
	/**
	 * Invoked by a BeanFactory after it has set all bean properties supplied
	 * (and satisfied BeanFactoryAware and ApplicationContextAware).
	 */
	void afterPropertiesSet() throws Exception;
}

  关于初始化的问题，还有其他几种方法实现

init-method、@PostConstruct、InitializingBean#afterPropertiesSet哪个先执行，这又是个问题

Constructor > @PostConstruct > InitializingBean > init-method，构造函数最优先

详见下面blog

http://sexycoding.iteye.com/blog/1046993