BeanFactory与FactoryBean的区别

首先二者从名称上就能看到区别，BeanFactory是Spring提供的存放Bean的工厂，FactoryBean是一个可生产Bean的工厂Bean。

FactoryBean

FactoryBean是Spring提供给用户自定义Bean的工厂Bean，隐藏创建对象的细节。
FactoryBean中有三个方法：

        // 用于返回Bean实例
    T getObject() throws Exception;
        // 返回Bean实例的class对象
    Class getObjectType();
        // 返回当前Bean的作用域，默认单例
        default boolean isSingleton() {
        return true;
    }

public class User {
  public void hello() {
      System.out.println("hello ...... ");
  }
}

public class UserFactoryBean implements FactoryBean {
    @Override
    public User getObject() throws Exception {
        return new User();
    }

    @Override
    public Class getObjectType() {
        return User.class;
    }
}
```java
public static void main(String[] args) throws Exception {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("application.xml");

                // 通过&可以在容器中取到FactoryBean本身的实例
        UserFactoryBean userFactoryBean = (UserFactoryBean) applicationContext.getBean("&userFactoryBean");
        User object = userFactoryBean.getObject();
        object.hello();
        
                // 这里调用getBean传入FactoryBean的名称返回的并不是FactoryBean本身，而是User
        User user = (User) applicationContext.getBean("userFactoryBean");
        user.hello();
    }