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怎么用FactoryBean讓Spring配置動起來
這篇文章主要介紹“怎么用Factory Bean讓Spring配置動起來”，在日常操作中，相信很多人在怎么用Factory Bean讓Spring配置動起來問題上存在疑惑，小編查閱了各式資料，整理出簡單好用的操作方法，希望對大家解答”怎么用Factory Bean讓Spring配置動起來”的疑惑有所幫助！接下來，請跟著小編一起來學習吧！
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不少朋友討論spring配置時認為spring配置中只能靜態的設置一些參數(典型情況如數據庫配置, 定時器配置等)導致不方便, 其實spring已經提供了非常便利的方式來實現動態spring配置, 我們要做的只是實現一個自己的 Factory Bean , 來看一下 Factory Bean 接口的定義
/**//**
* 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();
}
看了以后發現, Factory Bean 用于在spring容器中創建其他的Bean, 我們平時用得最多的 JndiObjectFactory Bean, hibernate 的 LocalSessionFactory Bean 都是 Factory Bean 的具體實現, 既然如此, 讀取動態配置就變得易如反掌了, 假如我們要實現動態讀取數據庫配置的功能, 拿使用率***的 BasicDatasource 為例, 簡單的實現一個 BasicDatasource Factory Bean 如下即可
public class BasicDataSourceFactoryBean implements FactoryBean ...{
public Object getObject() throws Exception ...{
BasicDataSource dataSource = new BasicDataSource();
// 讀取外部配置, 設置到 dataSource 中 ...
return dataSource;
}
public Class getObjectType() ...{
return BasicDataSource.class;
}
public boolean isSingleton() ...{
return true;
}
}
然后在 spring 中如此聲明
＜bean id="dataSource" class="BasicDataSourceFactoryBean "＞
... 你的配置來源
＜/bean＞
到此，關于“怎么用Factory Bean讓Spring配置動起來”的學習就結束了，希望能夠解決大家的疑惑。理論與實踐的搭配能更好的幫助大家學習，快去試試吧！若想繼續學習更多相關知識，請繼續關注創新互聯網站，小編會繼續努力為大家帶來更多實用的文章！
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