ConcurrentModificationException和一个HashMap

问题描述

我使用JPA持久化对象。主对象与另一个对象具有所有的一对多关系。另一个对象存储在HashMap中。什么样的同步会解决这个问题？它似乎发生在完全随机的时间，是非常不可预测的。这里是我得到的异常：

I am persisting objects using JPA. The Main object has an owning One-Many relationship with another object. The other object is stored in a HashMap. What sort of synchronization would fix this problem? It seems to happen at completely random times and is very unpredictable. Here is the exception I get:

Exception in thread "pool-1-thread-1" java.util.ConcurrentModificationException
        at java.util.HashMap$HashIterator.nextEntry(Unknown Source)
        at java.util.HashMap$ValueIterator.next(Unknown Source)
        at org.hibernate.collection.AbstractPersistentCollection$IteratorProxy.next(AbstractPersistentCollection.java:555)
        at org.hibernate.engine.Cascade.cascadeCollectionElements(Cascade.java:296)
        at org.hibernate.engine.Cascade.cascadeCollection(Cascade.java:242)
        at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:219)
        at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:169)
        at org.hibernate.engine.Cascade.cascade(Cascade.java:130)

推荐答案

这不是同步问题。

Iterator it = map.entrySet().iterator();
while (it.hasNext())
{
   Entry item = it.next();
   map.remove(item.getKey());
}

当it.hasNext（）被调用时，会抛出ConcurrentModificationException异常

This will throw a ConcurrentModificationException when the it.hasNext() is called the second time.

正确的方法是

   Iterator it = map.entrySet().iterator();
   while (it.hasNext())
   {
      Entry item = it.next();
      it.remove();
   }

假设此迭代器支持remove（）操作。

Assuming this iterator supports the remove() operation.

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