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编辑推荐：Spring开发资料合集 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。
编辑推荐：Spring开发资料合集 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。
下载本文示例代码
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