Spring一般通過反射機制利用BeanDefinition的class屬性指定實作類來執行個體化bean。有些場景下執行個體化bean比較複雜。按照傳統的方式,需要在<bean>中配置大量資訊。為了簡化這種操作,Spring提供了一個FactoryBean接口
public interface FactoryBean<T> { String OBJECT_TYPE_ATTRIBUTE = "factoryBeanObjectType"; @Nullable T getObject() throws Exception; //傳回建立的bean @Nullable Class<?> getObjectType(); //傳回建立的bean的類型 default boolean isSingleton() { return true; } }
Factory的使用
public class UserFactoryBean implements FactoryBean<User> { @Override public User getObject() throws Exception { return new User(); } @Override public Class<?> getObjectType() { return User.class; } @Override public boolean isSingleton() { return false; } }
<bean id="factoryBean" class="com.springboot2.test.UserFactoryBean"/>
XmlBeanFactory beanFactory = new XmlBeanFactory(new ClassPathResource("beans.xml")); User user = (User)beanFactory.getBean("factoryBean"); user.showMe();