Java 序列化ehcache中的元素时出错

在将元素放入ehcache时，我遇到以下错误。有人知道为什么会发生这个错误吗

先谢谢你

这种方法是：

  @SuppressWarnings("unchecked")
  @Override
  public void putActivity(Activity activity) {
    // put activity itself
    Serializable activityKey = KEY_PREFIX_ACTIVITY + activity.getId();
    final Element activityElement = new Element(activityKey, activity);
    getCache().put(activityElement);

    // add activity to the list of user
    ArrayList<Activity> activities = null;
    Serializable userKey = KEY_PREFIX_USER_ACTIVITIES + activity.getExecutingUserId();
    Element userActivities = getCache().get(userKey);
    if (userActivities == null) {
      activities = new ArrayList<Activity>();
      userActivities = new Element(userKey, activities);
    } else {
      activities = (ArrayList<Activity>) userActivities.getObjectValue();
    }
    activities.add(activity);
    getCache().put(userActivities);
  }

以下是ehcache源代码中的更多详细信息：

    private MemoryEfficientByteArrayOutputStream  [More ...] serializeElement(Element element) throws IOException {

         // A ConcurrentModificationException can occur because Java's serialization


         // mechanism is not threadsafe and POJOs are seldom implemented in a threadsafe way.


         // e.g. we are serializing an ArrayList field while another thread somewhere in the application is appending to it.


         try {



             return MemoryEfficientByteArrayOutputStream.serialize(element);



         } catch (ConcurrentModificationException e) {


             throw new CacheException("Failed to serialize element due to ConcurrentModificationException. " +


                                      "This is frequently the result of inappropriately sharing thread unsafe object " +


                                      "(eg. ArrayList, HashMap, etc) between threads", e);


         }



  }

---

您正在更新序列化的对象，请尝试将其保存到磁盘。应该只在缓存中存储不可变对象

在您的情况下，不要尝试重用ArrayList，请创建一个新的ArrayList：

if (userActivities == null) {
      activities = new ArrayList<Activity>();
      userActivities = new Element(userKey, activities);
} else {
      activities = new ArrayList<Activity>((List) userActivities.getObjectValue());
}

---

您可以实例化CopyOnWriteArrayList而不是ArrayList。

谢谢，您的意思是这样吗？else{activities=new ArrayList；activities.addAllArrayList userActivities.getObjectValue；}是的，我忘记了强制转换

if (userActivities == null) {
      activities = new ArrayList<Activity>();
      userActivities = new Element(userKey, activities);
} else {
      activities = new ArrayList<Activity>((List) userActivities.getObjectValue());
}