Nacos+@RefreshScope 为什么配置能动态刷新？

/**
 * Convenience annotation to put a <code>@Bean</code> definition in
 * {@link org.springframework.cloud.context.scope.refresh.RefreshScope refresh scope}.
 * Beans annotated this way can be refreshed at runtime and any components that are using
 * them will get a new instance on the next method call, fully initialized and injected
 * with all dependencies.
 *
 * @author Dave Syer
 *
 */
@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Scope("refresh")
@Documented
public @interface RefreshScope {
 /**
  * @see Scope#proxyMode()
  * @return proxy mode
  */
 ScopedProxyMode proxyMode() default ScopedProxyMode.TARGET_CLASS;
}

public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {
protected <T> T doGetBean(
   String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
   throws BeansException {
    // 如果scope是单例的情况, 这里不进行分析
    if (mbd.isSingleton()) {
     .....
    }
                // 如果scope是prototype的情况, 这里不进行分析
    else if (mbd.isPrototype()) {
     ......
    }
                // 如果scope是其他的情况，本例中是reresh
    else {
     String scopeName = mbd.getScope();
     if (!StringUtils.hasLength(scopeName)) {
      throw new IllegalStateException("No scope name defined for bean '" + beanName + "'");
     }
                    // 获取refresh scope的实现类RefreshScope，这个类在哪里注入，我们后面讲
     Scope scope = this.scopes.get(scopeName);
     if (scope == null) {
      throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
     }
     try {
                        // 这边是获取bean,调用的是RefreshScope中的的方法
      Object scopedInstance = scope.get(beanName, () -> {
       beforePrototypeCreation(beanName);
       try {
        return createBean(beanName, mbd, args);
       }
       finally {
        afterPrototypeCreation(beanName);
       }
      });
      beanInstance = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
     }
     catch (IllegalStateException ex) {
      throw new ScopeNotActiveException(beanName, scopeName, ex);
     }
    }
   }
   catch (BeansException ex) {
    beanCreation.tag("exception", ex.getClass().toString());
    beanCreation.tag("message", String.valueOf(ex.getMessage()));
    cleanupAfterBeanCreationFailure(beanName);
    throw ex;
   }
   finally {
    beanCreation.end();
   }
  }
  return adaptBeanInstance(name, beanInstance, requiredType);
 }
}

public class GenericScope
  implements Scope, BeanFactoryPostProcessor, BeanDefinitionRegistryPostProcessor, DisposableBean {
                 @Override
  public Object get(String name, ObjectFactory<?> objectFactory) {
  // 将bean添加到缓存cache中
        BeanLifecycleWrapper value = this.cache.put(name, new BeanLifecycleWrapper(name, objectFactory));
  this.locks.putIfAbsent(name, new ReentrantReadWriteLock());
  try {
            // 调用下面的getBean方法
   return value.getBean();
  }
  catch (RuntimeException e) {
   this.errors.put(name, e);
   throw e;
  }
 }       
private static class BeanLifecycleWrapper {
  public Object getBean() {
            // 如果bean为空，则创建bean
   if (this.bean == null) {
    synchronized (this.name) {
     if (this.bean == null) {
      this.bean = this.objectFactory.getObject();
     }
    }
   }
            // 否则返回之前创建好的bean
   return this.bean;
  }
            }
        }

public class RefreshEventListener implements SmartApplicationListener {
........
 public void handle(RefreshEvent event) {
  if (this.ready.get()) { // don't handle events before app is ready
   log.debug("Event received " + event.getEventDesc());
            // 会调用refresh方法，进行刷新
   Set<String> keys = this.refresh.refresh();
   log.info("Refresh keys changed: " + keys);
  }
 }
}
// 这个是ContextRefresher类中的刷新方法
public synchronized Set<String> refresh() {
        // 刷新spring的envirionment 变量配置
  Set<String> keys = refreshEnvironment();
        // 刷新其他scope
  this.scope.refreshAll();
  return keys;
 }

public class RefreshScope extends GenericScope
  implements ApplicationContextAware, ApplicationListener<ContextRefreshedEvent>, Ordered {
 @ManagedOperation(description = "Dispose of the current instance of all beans "
   + "in this scope and force a refresh on next method execution.")
 public void refreshAll() {
  // 调用父类的destroy
        super.destroy();
  this.context.publishEvent(new RefreshScopeRefreshedEvent());
 }
}
@Override
 public void destroy() {
  List<Throwable> errors = new ArrayList<Throwable>();
  Collection<BeanLifecycleWrapper> wrappers = this.cache.clear();
  for (BeanLifecycleWrapper wrapper : wrappers) {
   try {
    Lock lock = this.locks.get(wrapper.getName()).writeLock();
    lock.lock();
    try {
                    // 这里主要就是把之前的bean设置为null, 就会重新走createBean的流程了
     wrapper.destroy();
    }
    finally {
     lock.unlock();
    }
   }
   catch (RuntimeException e) {
    errors.add(e);
   }
  }
  if (!errors.isEmpty()) {
   throw wrapIfNecessary(errors.get(0));
  }
  this.errors.clear();
 }