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> {

    @Override

    public 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();

    }

    @Override

    public Class<?> getObjectType() {

        return User.class;

    }

    @Override

    public 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 {

    @Autowired

    private BeanFactory beanFactory;

    @Test

    public void test() {

        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getObjectFromFactoryBean

        object = getObjectFromFactoryBean(factory, beanName, !synthetic);

    }

    return object;

}