@Resource注入原理

示例

在工程中我们有时也会使用@Resource注解来注入对象，例如下面代码：在E类中注入RF和G的对象实例

@Component
public class E {
    @Resource
    RF rf;
    @Resource
    G g;
}

@Component
public class RF {
}

@Component
public class G {
}

注入原理分析

在使用Resource注入时，其主要逻辑由CommonAnnotationBeanPostProcessor#autowireResource方法实现

核心代码

protected Object autowireResource(BeanFactory factory, LookupElement element, @Nullable String requestingBeanName)
            throws NoSuchBeanDefinitionException {

        Object resource;
        Set<String> autowiredBeanNames;
        String name = element.name;

        if (factory instanceof AutowireCapableBeanFactory) {
            AutowireCapableBeanFactory beanFactory = (AutowireCapableBeanFactory) factory;
            DependencyDescriptor descriptor = element.getDependencyDescriptor();
            // @Resource和@Autowired的区别
            // 有没有自定义名字，如果有再去判断名字是否有对应的bean
            if (this.fallbackToDefaultTypeMatch && element.isDefaultName && !factory.containsBean(name)) {
                autowiredBeanNames = new LinkedHashSet<>();
                // 与autowired保持相同逻辑
                resource = beanFactory.resolveDependency(descriptor, requestingBeanName, autowiredBeanNames, null);
                if (resource == null) {
                    throw new NoSuchBeanDefinitionException(element.getLookupType(), "No resolvable resource object");
                }
            }
            else {
                resource = beanFactory.resolveBeanByName(name, descriptor);
                autowiredBeanNames = Collections.singleton(name);
            }
        }
        else {
            resource = factory.getBean(name, element.lookupType);
            autowiredBeanNames = Collections.singleton(name);
        }

        if (factory instanceof ConfigurableBeanFactory) {
            ConfigurableBeanFactory beanFactory = (ConfigurableBeanFactory) factory;
            for (String autowiredBeanName : autowiredBeanNames) {
                if (requestingBeanName != null && beanFactory.containsBean(autowiredBeanName)) {
                    beanFactory.registerDependentBean(autowiredBeanName, requestingBeanName);
                }
            }
        }

        return resource;
    }

注入原理