怎么用FactoryBean让Spring配置动起来
这篇文章主要介绍“怎么用Factory Bean让Spring配置动起来”，在日常操作中，相信很多人在怎么用Factory Bean让Spring配置动起来问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答”怎么用Factory Bean让Spring配置动起来”的疑惑有所帮助！接下来，请跟着小编一起来学习吧！
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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spring配置, 我们要做的只是实现一个自己的 Factory Bean , 来看一下 Factory Bean 接口的定义
/**//**
* 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, Factory Bean 用于在spring容器中创建其他的Bean, 我们平时用得最多的 JndiObjectFactory Bean, hibernate 的 LocalSessionFactory Bean 都是 Factory Bean 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***的 BasicDatasource 为例, 简单的实现一个 BasicDatasource Factory Bean 如下即可
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
＜bean id="dataSource" class="BasicDataSourceFactoryBean "＞
... 你的配置来源
＜/bean＞
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