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发表时间:2006-11-01
/** * 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 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> 就这么简单 声明:ITeye文章版权属于作者,受法律保护。没有作者书面许可不得转载。
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发表时间:2006-11-01
自己定义FactoryBean!要求其对外接口一致,且其重用性强!
多数情况下,非较模块化的功能,不会自己定义FactoryBean! 松散的结构(非高内聚)频繁使用FB,会导致注入泛滥!难以管理! 一般情况下,好像FactoryBean多用于框架! 另,对于未纳入spring的framework而言,可以被轻松并入spring管理,做一个独一无二的生产管理者! |
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发表时间:2006-11-02
org.springframework.aop.target.dynamic.AbstractRefreshableTargetSource;
org.springframework.aop.target.HotSwappableTargetSource; |
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发表时间:2006-11-03
和标题比较匹配的应该是BeanFactoryPostProcessor和BeanPostProcessor
这是两个很大很大的Aspect,一切尽在掌握。。。 ![]() |
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发表时间:2006-11-03
没有看明白,// 读取外部配置, 设置到 dataSource 中 ...,这和在spring中创建一个bean时配置属性有什么不同啊?通过设置一个BasicDataSource ,再refbean不可以吗?
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发表时间:2006-11-04
kimfly 写道 没有看明白,// 读取外部配置, 设置到 dataSource 中 ...,这和在spring中创建一个bean时配置属性有什么不同啊?通过设置一个BasicDataSource ,再refbean不可以吗?
通常的设置方式是这样 <bean id="system.datasource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"> <property name="driverClassName" value="${jdbc.driverClassName}" /> <property name="url" value="${jdbc.url}"/> <property name="username" value="${jdbc.username}"/> <property name="password" value="${jdbc.password}"/> </bean> 虽然可以从 properties 等文件读取, 但还是有一定的局限性, 使用 FactoryBean 可以从任意来源读取, 当然这只是个示例, 一般数据库的配置都是固定的, 只是为了说明这种用法 |
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发表时间:2006-11-11
简单易懂!
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发表时间:2006-12-09
还是没有体会到楼主的深意啊,惭愧。
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发表时间:2006-12-10
要把某某框架与Spring集成的时候就很依赖FactoryBean,比如要读入JBossRules的规则文件,生成一个RuleBase,就可以用FB返回一个RuleBase,而JBoss Seam中貌似没有类似机制,只好自己又包了一个叫org...seam.RuleBase的物体。
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发表时间:2007-01-24
好文章,解决了我的一个历史问题
我希望jms动态的读取值设定jmsListenerContainer的messageSelector属性(因为系统登录者是无法事先确定的) 我原先是用一个丑陋的静态方法作为bean的属性的来源,在代码里设定值以后,然后再刷新spingContext 但还不知道能否在spring配置文件里写条件表达式启动时动态设值,可以做到像rails那样简单的设定一个环境变量从而启动不同的运行配置环境,博主请指教。 |
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