Spring AbstractRequestAttributesScope

@Override
public Object get(String name, ObjectFactory<?> objectFactory) {
   // 获取当前 request 的属性对象
   RequestAttributes attributes = RequestContextHolder.currentRequestAttributes();
   // 属性对象中获取 name 对应的属性实例
   Object scopedObject = attributes.getAttribute(name, getScope());
   if (scopedObject == null) {
      // object factory 创建
      scopedObject = objectFactory.getObject();
      // 设置到 request attributes 中
      attributes.setAttribute(name, scopedObject, getScope());
      // Retrieve object again, registering it for implicit session attribute updates.
      // As a bonus, we also allow for potential decoration at the getAttribute level.

      // 再一次获取
      Object retrievedObject = attributes.getAttribute(name, getScope());
      if (retrievedObject != null) {
         // Only proceed with retrieved object if still present (the expected case).
         // If it disappeared concurrently, we return our locally created instance.
         scopedObject = retrievedObject;
      }
   }
   return scopedObject;
}

protected abstract int getScope();

RequestAttributes#SCOPE_REQUEST
RequestAttributes#SCOPE_SESSION

@Override
@Nullable
public Object remove(String name) {
   // 获取当前 request attributes 对象
   RequestAttributes attributes = RequestContextHolder.currentRequestAttributes();
   // 通过 name + 作用域 获取 属性实例
   Object scopedObject = attributes.getAttribute(name, getScope());
   if (scopedObject != null) {
      // 删除属性实例
      attributes.removeAttribute(name, getScope());
      return scopedObject;
   }
   else {
      return null;
   }
}

@Override
public void registerDestructionCallback(String name, Runnable callback) {
   RequestAttributes attributes = RequestContextHolder.currentRequestAttributes();
   attributes.registerDestructionCallback(name, callback, getScope());
}

@Override
@Nullable
public Object resolveContextualObject(String key) {
   RequestAttributes attributes = RequestContextHolder.currentRequestAttributes();
   return attributes.resolveReference(key);
}

public class RequestScope extends AbstractRequestAttributesScope {

   @Override
   protected int getScope() {
      return RequestAttributes.SCOPE_REQUEST;
   }

   /**
    * There is no conversation id concept for a request, so this method
    * returns {@code null}.
    */
   @Override
   @Nullable
   public String getConversationId() {
      return null;
   }

}

public class SessionScope extends AbstractRequestAttributesScope {

   @Override
   protected int getScope() {
      return RequestAttributes.SCOPE_SESSION;
   }

   @Override
   public String getConversationId() {
      return RequestContextHolder.currentRequestAttributes().getSessionId();
   }

   @Override
   public Object get(String name, ObjectFactory<?> objectFactory) {
      Object mutex = RequestContextHolder.currentRequestAttributes().getSessionMutex();
      synchronized (mutex) {
         return super.get(name, objectFactory);
      }
   }

   @Override
   @Nullable
   public Object remove(String name) {
      Object mutex = RequestContextHolder.currentRequestAttributes().getSessionMutex();
      synchronized (mutex) {
         return super.remove(name);
      }
   }

}