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＞＜b＞note:＜/b＞ autowiring will simply ignore factorybeans that return 　* ＜code＞null＜/code＞ here. therefore it is highly recommended to implement 　* this method properly, using the current state of the factorybean. 　* @return the type of object that this factorybean creates, 　* or ＜code＞null＜/code＞ if not known at the time of the call 　* @see listablebeanfactory#getbeansoftype 　*/ 　class getobjecttype(); 　/** 　* is the bean managed by this factory a singleton or a prototype? 　* that is, will ＜code＞getobject()＜/code＞ always return the same object 　* (a reference that can be cached)? 　* ＜p＞＜b＞note:＜/b＞ if a factorybean indicates to hold a singleton object, 　* the object returned from ＜code＞getobject()＜/code＞ might get cached 　* by the owning beanfactory. hence, do not return ＜code＞true＜/code＞ 　* unless the factorybean always exposes the same reference. 　* ＜p＞the singleton status of the factorybean itself will generally 　* be provided by the owning beanfactory; usually, it has to be 　* defined as singleton there. 　* @return if this bean is a singleton 　* @see #getobject() 　*/ 　boolean issingleton(); }

　　看了以后发现, factorybean 用于在 spring 容器中创建其他的 bean, 我们平时用得最多的 jndiobjectfactorybean, hibernate 的 localsessionfactorybean 都是 factorybean 的具体实现, 既然如此, 读取动态配置就变得易如反掌了, 假如我们要实现动态读取数据库配置的功能, 拿使用率最高的 basicdatasource 为例, 简单的实现一个 basicdatasource factorybean 如下即可

　　代码

public class basicdatasourcefactorybean implements factorybean { 　public object getobject() throws exception { 　　basicdatasource datasource = new basicdatasource(); 　　// 读取外部配置, 设置到 datasource 中 ... 　　return datasource; 　} 　public class getobjecttype() { 　　return basicdatasource.class; 　} 　public boolean issingleton() { 　　return true; 　} }

　　然后在 spring 中如此声明

　　代码

＜bean id="datasource" class="basicdatasourcefactorybean "＞ ... 你的配置来源 ＜/bean＞

　　就这么简单。