/*** 实现此接口的bean不能用作普通bean。此bean暴露的对象是通过getObject()创建的对象，而不是它自身*/
public interface FactoryBean<T> {/*** 返回此工厂管理的对象的实例（可能是共享的或独立的，取决于isSingleton()的返回值）*/@NullableT getObject() throws Exception;/*** 返回此FactoryBean创建的对象类型,*/@NullableClass<?> getObjectType();/*** 该工厂管理的对象是否为单例?* 如果是(return true),getObject()总是返回同一个共享的实例，该对象会被BeanFactory缓存起来* 如果是(return false),getObject()返回独立的实例* 一般情况下返回true*/default boolean isSingleton() {return true;}
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans-4.1.xsd"><bean id="user" class="com.lee.factorybean.User"><property name="name" value="zhangsan"/></bean>
</beans>

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans-4.1.xsd"><bean id="user" class="com.lee.factorybean.config.UserFactoryBean" />
</beans>

package com.lee.factorybean.config;
import com.lee.factorybean.entity.User;
import org.springframework.beans.factory.FactoryBean;
public class UserFactoryBean implements FactoryBean<User> {@Overridepublic User getObject() throws Exception {// 假设User的实例化过程比较复杂，在此处进行User的实例化return new User();}@Overridepublic Class<?> getObjectType() {return User.class;}@Overridepublic boolean isSingleton() {return true;}
}

package com.lee.factorybean.config;
import com.lee.factorybean.entity.User;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.stereotype.Component;
@Component("user")          // beanName = user
public class UserFactoryBean implements FactoryBean<User> {@Overridepublic User getObject() throws Exception {// 假设User的实例化过程比较复杂，在此处进行User的实例化return new User();}@Overridepublic Class<?> getObjectType() {return User.class;}@Overridepublic boolean isSingleton() {return true;}
}

package com.lee.factorybean.entity;
public class User {private Integer id;private String name;private Integer age;public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}
}

package com.lee.factorybean.test;
import com.lee.factorybean.FactoryBeanApplication;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
@RunWith(SpringRunner.class)
@SpringBootTest
public class FactoryBeanTest {@Autowiredprivate BeanFactory beanFactory;@Testpublic void test() {Object user = beanFactory.getBean("user");System.out.println(user.getClass().getName());}
}

@Test
public void test() {// 断点入口Object user = beanFactory.getBean("user");System.out.println(user.getClass().getName());
}

bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
/*** 获取实例对象* 可能是beanInstance自身，也可能是beanInstance创建的对象(如果beanInstance是FactoryBean类型)*/
protected Object getObjectForBeanInstance(Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {// name以工厂引用(&)开头，可以跟下isFactoryDereference方法if (BeanFactoryUtils.isFactoryDereference(name)) {if (beanInstance instanceof NullBean) {return beanInstance;}// 如果name以&开头，而beanInstance不是FactoryBean类型，则抛异常（我们没按spring规则来使用）if (!(beanInstance instanceof FactoryBean)) {throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());}}// 如果beanInstance不是FactoryBean类型，则直接返回beanInstance// 或者name以&开头，也直接返回beanInstance，说明我们就想获取FactoryBean实例if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {return beanInstance;}Object object = null;if (mbd == null) {object = getCachedObjectForFactoryBean(beanName);}if (object == null) {// 此时beanInstance是FactoryBean类型，而name又不是以&开头; 这是我们示例工程的情况，也是最普通、用的最多的情况// 将beanInstance强转成FactoryBean类型FactoryBean<?> factory = (FactoryBean<?>) beanInstance;// 从缓存中获取我们需要的实例对象if (mbd == null && containsBeanDefinition(beanName)) {mbd = getMergedLocalBeanDefinition(beanName);}boolean synthetic = (mbd != null && mbd.isSynthetic());// 调用FactoryBean的getObject方法创建我们需要的实例对象；大家自行跟下getObjectFromFactoryBeanobject = getObjectFromFactoryBean(factory, beanName, !synthetic);}return object;
}

@Test
public void test() {Object user = beanFactory.getBean("&user");System.out.println(user.getClass().getName());
}

com.lee.factorybean.config.UserFactoryBean