看到不少朋友討論 sPRing 配置時(shí)認(rèn)為 spring 配置中只能靜態(tài)的設(shè)置一些參數(shù)(典型情況如數(shù)據(jù)庫(kù)配置, 定時(shí)器配置等)導(dǎo)致不方便, 其實(shí) spring 已經(jīng)提供了非常便利的方式來(lái)實(shí)現(xiàn)動(dòng)態(tài)配置, 我們要做的只是實(shí)現(xiàn)一個(gè)自己的 FactoryBean , 來(lái)看一下 FactoryBean 接口的定義
代碼
/** * 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＞
