Spring注解@DependsOn解析

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface DependsOn {

	String[] value() default {};

@Component
@DependsOn(value = {"dependsOnBeanB"})
public class DependsOnBeanA {

}

static void processCommonDefinitionAnnotations(AnnotatedBeanDefinition abd, AnnotatedTypeMetadata metadata) {
    //省略若干代码
		AnnotationAttributes dependsOn = attributesFor(metadata, DependsOn.class);
		if (dependsOn != null) {
			  abd.setDependsOn(dependsOn.getStringArray("value"));
		}
	}

 protected <T> T doGetBean(String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
            throws BeansException {
        RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
        // Guarantee initialization of beans that the current bean depends on.
        String[] dependsOn = mbd.getDependsOn();
        if (dependsOn != null) {
            for (String dep : dependsOn) {
                if (isDependent(beanName, dep)) {
                    throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                            "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
                }
                    registerDependentBean(dep, beanName);
                try {
                    getBean(dep);
                } catch (NoSuchBeanDefinitionException ex) {
                    throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                            "'" + beanName + "' depends on missing bean '" + dep + "'", ex);
                }
            }
        }
    }