public interface FactoryBean<T> {
	//获取FactoryBean初始化的Bean实例
	T getObject() throws Exception;
	//获取Bean实例的类型
	Class<?> getObjectType();
	//判断是否是单例模式
	boolean isSingleton();
}

创建MyFactoryBean:

public class MyFactoryBean implements FactoryBean<Date>,BeanNameAware {  
    private String name;  
    @Override  
    public Date getObject() throws Exception {  
        return new Date();  
    }  
    @Override  
    public Class<?> getObjectType() {  
        return Date.class;  
    }  
    @Override  
    public boolean isSingleton() {  
        return false;  
    }  
    public void sayName() {  
        System.out.println("My name is " + this.name);  
    }  
    @Override  
    public void setBeanName(String name) {  
        this.name = name;  
    }  
}  

在Spring的配置文件ApplicationContext.xml中注入MyFactoryBean

<bean id ="myFactoryBean" class="com.xxxx.MyFactoryBean"></bean>

测试代码

public class MainFactoryBean {

	@SuppressWarnings("resource")
	public static void main(String [] args){  
		ApplicationContext appCtx = new ClassPathXmlApplicationContext("applicationContext.xml");
	    Date now = (Date) appCtx.getBean("myFactoryBean");  
	    System.out.println(now);  
	    MyFactoryBean factoryBean = (MyFactoryBean) appCtx.getBean("&myFactoryBean");  
	    factoryBean.sayName();  
	}  
}

运行结果：通过myFactoryBean名称获取到的Bean是Date对象实例，通过&myFactoryBean获取到的是MyFactoryBean对象实例。

4、实现原理

@Override
	public Object getBean(String name) throws BeansException {
		return doGetBean(name, null, null, false);
	}

doGetBean中获取bean实例

protected <T> T doGetBean(
			final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
			throws BeansException {
		.........//省略部分代码
		bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
		.........//省略部分代码
		return (T) bean;
	}

getObjectForBeanInstance中会选择bean实例是普通的Bean还是FactoryBean，同时通过判断name中是否有&来选择判断是或者FactoryBean还是其getObject方法中获取的bean

protected Object getObjectForBeanInstance(
			Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {
		.........//省略部分代码
		//判断bean类型是否是FactoryBean，或者name是否是以&开头，如果是则直接返回
		if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
			return beanInstance;
		}
		//如果是则从getObjectFromFactoryBean中获取
		if (object == null) {
			// Return bean instance from factory.
			FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
			if (mbd == null && containsBeanDefinition(beanName)) {
				mbd = getMergedLocalBeanDefinition(beanName);
			}
			boolean synthetic = (mbd != null && mbd.isSynthetic());
			object = getObjectFromFactoryBean(factory, beanName, !synthetic);
		}
		return object;
	}

getObjectFromFactoryBean接下来会执行FactoryBean的getObject方法获取bean了。

protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) {
		.........//省略部分代码				
		Object object = doGetObjectFromFactoryBean(factory, beanName);
		.........//省略部分代码
		return object;
	}
	
private Object doGetObjectFromFactoryBean(final FactoryBean<?> factory, final String beanName)
			throws BeanCreationException {
		Object object;
		.........//省略部分代码
		//调用Factory的getObject方法
		object = factory.getObject();
		.........//省略部分代码
		return object;
	}

总结：Spring对FactoryBean的实现机制是当你获取一个Bean时，如果获取的Bean的类型是FactoryBean，并且其name中并没有&则调用bean的getObject方法获取FactoryBean实现类中提供bean，否则就是直接返回普通的bean类型。