1. 它的作用是用制造創建過程較為復雜的產品, 如 SqlSessionFactory, 但 @Bean 已具備等價功能

2. 使用

   1. 被 FactoryBean 創建的產品

      • 會認為創建、依賴注入、Aware 接口回調、前初始化這些都是 FactoryBean 的職責, 這些流程都不會走

      • 唯有后初始化的流程會走, 也就是產品可以被代理增強

      • 單例的產品不會存儲于 BeanFactory 的 singletonObjects 成員中, 而是另一個 factoryBeanObjectCache 成員中

   2. 按名字去獲取時, 拿到的是產品對象, 名字前面加 & 獲取的是工廠對象

3. 在spring中，前此接口的實現仍被大量使用, 想被全面廢棄很難

package com.butch.a43;import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.ComponentScan;@ComponentScan
public class A43 {public static void main(String[] args) {AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A43.class);//一部分被spring容器管理 創建的時候沒有autowird 初始化及aware，初始化后會管理 如aopBean1 bean1 = (Bean1) context.getBean("bean1");Bean1 bean2 = (Bean1) context.getBean("bean1");Bean1 bean3 = (Bean1) context.getBean("bean1");System.out.println(bean1);System.out.println(bean2);System.out.println(bean3);System.out.println(context.getBean(Bean1.class));System.out.println(context.getBean(Bean1FactoryBean.class));System.out.println(context.getBean("&bean1"));context.close();}}

?

package com.butch.a43;import org.springframework.stereotype.Component;@Component
public class Bean2 {
}

package com.butch.a43;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;@Component
public class Bean1PostProcessor implements BeanPostProcessor {private static final Logger log = LoggerFactory.getLogger(Bean1PostProcessor.class);@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {if (beanName.equals("bean1") && bean instanceof Bean1) {log.debug("before [{}] init", beanName);}return bean;}@Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {if (beanName.equals("bean1") && bean instanceof Bean1) {log.debug("after [{}] init", beanName);}return bean;}
}

package com.butch.a43;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.stereotype.Component;@Component("bean1")
public class Bean1FactoryBean implements FactoryBean<Bean1> {private static final Logger log = LoggerFactory.getLogger(Bean1FactoryBean.class);// 決定了根據【類型】獲取或依賴注入能否成功@Overridepublic Class<?> getObjectType() {return Bean1.class;}// 決定了 getObject() 方法被調用一次還是多次@Overridepublic boolean isSingleton() {return true;}@Overridepublic Bean1 getObject() throws Exception {Bean1 bean1 = new Bean1();log.debug("create bean: {}", bean1);return bean1;}
}

package com.butch.a43;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.annotation.Autowired;import javax.annotation.PostConstruct;public class Bean1 implements BeanFactoryAware {private static final Logger log = LoggerFactory.getLogger(Bean1.class);private Bean2 bean2;@Autowiredpublic void setBean2(Bean2 bean2) {log.debug("setBean2({})", bean2);this.bean2 = bean2;}public Bean2 getBean2() {return bean2;}@PostConstructpublic void init() {log.debug("init");}@Overridepublic void setBeanFactory(BeanFactory beanFactory) throws BeansException {log.debug("setBeanFactory({})", beanFactory);}
}