spring学习总结011 --- FactoryBean

FactoryBean是spring提供的一个接口，交由用户自己实现bean实例化方法，接口如下：

实例：

public class FactoryBeanInfo implements BeanNameAware {
    private int id;
    private String name;
    private String beanName;

    @Override
    public void setBeanName(String name) {
        this.beanName = name;
    }
}

@Component
public class MyFactoryBean implements FactoryBean<FactoryBeanInfo> {

    @Override
    public FactoryBeanInfo getObject() throws Exception {
        return FactoryBeanInfo.builder().id(1).name("bale").build();
    }

    @Override
    public Class<?> getObjectType() {
        return FactoryBeanInfo.class;
    }

    @Override
    public boolean isSingleton() {
        return true;
    }
}

@Slf4j
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = {FactoryBeanConfig.class})
public class FactoryBeanTest {

    @Autowired
    private ApplicationContext applicationContext;

    @Test
    public void test_factoryBean_base() {
        String[] beanDefinitionNames = applicationContext.getBeanDefinitionNames();
        log.info("Bean definition names:{}", Arrays.toString(beanDefinitionNames));

        FactoryBeanInfo factoryBeanInfo = applicationContext.getBean(FactoryBeanInfo.class);
        log.warn("Factory bean info:{}", factoryBeanInfo); // 没有拿到beanName
    }
}

运行结果：

[main] INFO org.springframework.test.context.support.DefaultTestContextBootstrapper - Loaded default TestExecutionListener class names from location [META-INF/spring.factories]: [org.springframework.test.context.web.ServletTestExecutionListener, org.springframework.test.context.support.DirtiesContextBeforeModesTestExecutionListener, org.springframework.test.context.support.DependencyInjectionTestExecutionListener, org.springframework.test.context.support.DirtiesContextTestExecutionListener, org.springframework.test.context.transaction.TransactionalTestExecutionListener, org.springframework.test.context.jdbc.SqlScriptsTestExecutionListener, org.springframework.test.context.event.EventPublishingTestExecutionListener]
[main] INFO org.springframework.test.context.support.DefaultTestContextBootstrapper - Using TestExecutionListeners: [org.springframework.test.context.support.DirtiesContextBeforeModesTestExecutionListener@3c0ecd4b, org.springframework.test.context.support.DependencyInjectionTestExecutionListener@14bf9759, org.springframework.test.context.support.DirtiesContextTestExecutionListener@5f341870, org.springframework.test.context.event.EventPublishingTestExecutionListener@553f17c]
[main] INFO com.demo.FactoryBeanTest - Bean definition names:[org.springframework.context.annotation.internalConfigurationAnnotationProcessor, org.springframework.context.annotation.internalAutowiredAnnotationProcessor, org.springframework.context.annotation.internalCommonAnnotationProcessor, org.springframework.context.event.internalEventListenerProcessor, org.springframework.context.event.internalEventListenerFactory, factoryBeanConfig, myFactoryBean]
[main] WARN com.demo.FactoryBeanTest - Factory bean info:FactoryBeanInfo(id=1, name=bale, beanName=null)

Process finished with exit code 0

有两个问题要分析：

1、FactoryBeanInfo很明显不是在容器创建的时候创建的，是在getBean的时候创建的，那么FactoryBeanInfo创建流程是什么？

2、FactoryBeanInfo明明实现了BeanNameAware接口，但是spring为什么没有为其填充beanName？

FactoryBeanInfo创建流程

主要的创建流程在AbstractBeanFactory#isTypeMatch方法和AbstractBeanFactory#getTypeForFactoryBean方法中：

总结起来就是：getBean过程中先获取已经解析好的bean定义，获取到beanNames，遍历beanNames，并获取bean实例；如果bean类型是FactoryBean，那么调用FactoryBean的getObjectType获取需要创建的bean的className；

接下来就是getBean ---> doGetBean很熟悉的流程；

需要注意的就是保证getObjectType和getObject返回的对象类型一致

实现了BeanNameAware接口，为什么没有为其填充beanName

接着上面的流程，doGetBean传入的参数beanName为MyFactoryBean，requiredType为FactoryBeanInfo：

因此先从单例池中拿到myBeanFactory实例，最终调用MyFactoryBean的getObject方法：

 所以，BeanNameAware未生效的原因为：FactoryBean中自定义Bean实例创建方法并未走createInstance --> populateBean  ---> initializeBean方法