用FactoryBean让Spring配置动起来

　　看到不少朋友讨论 spring 配置时认为 spring 配置中只能静态的设置一些参数(典型情况如数据库配置, 定时器配置等)导致不方便, 其实 spring 已经提供了非常便利的方式来实现动态配置, 我们要做的只是实现一个自己的 FactoryBean , 来看一下 FactoryBean 接口的定义

　　代码

/**
* Interface to be implemented by objects used within a BeanFactory
* that are themselves factories. If a bean implements this interface,
* it is used as a factory, not directly as a bean.
*
* ＜p＞＜b＞NB: A bean that implements this interface cannot be used
* as a normal bean.＜/b＞ A FactoryBean is defined in a bean style,
* but the object eXPosed for bean references is always the object
* that it creates.
*
* ＜p＞FactoryBeans can support singletons and prototypes, and can
* either create objects lazily on demand or eagerly on startup.
*
* ＜p＞This interface is heavily used within the framework, for
* example for the AOP ProxyFactoryBean or JndiObjectFactoryBean.
* It can be used for application components, but this is not common
* outside of infrastrUCture code.
*
* @author Rod Johnson
* @author Juergen Hoeller
* @since 08.03.2003
* @see org.springframework.beans.factory.BeanFactory
* @see org.springframework.aop.framework.ProxyFactoryBean
* @see org.springframework.jndi.JndiObjectFactoryBean
*/
public interface FactoryBean {

　/**
　* Return an instance (possibly shared or independent) of the object
　* managed by this factory. As with a BeanFactory, this allows
　* support for both the Singleton and Prototype design pattern.
　* ＜p＞If this method returns ＜code＞null＜/code＞, the factory will consider
　* the FactoryBean as not fully initialized and throw a corresponding
　* FactoryBeanNotInitializedException.
　* @return an instance of the bean (should not be ＜code＞null＜/code＞;
　* a ＜code＞null＜/code＞ value will be considered as an indication of
　* incomplete initialization)
　* @throws Exception in case of creation errors
　* @see FactoryBeanNotInitializedException
　*/
　Object getObject() throws Exception;

　/**
　* Return the type of object that this FactoryBean creates, or ＜code＞null＜/code＞
　* if not known in advance. This allows to check for specific types
　* of beans without instantiating objects, for example on autowiring.
　* ＜p＞For a singleton, this should try to avoid singleton creation
　* as far as possible; it should rather estimate the type in advance.
　* For prototypes, returning a meaningful type here is advisable too.
　* ＜p＞This method can be called ＜i＞before＜/i＞ this FactoryBean has
　* been fully initialized. It must not rely on state created during
　* initialization; of course, it can still use such state if available.
　* ＜p＞