GAE Exception: ObjectManager has been closed

转载于 2011-04-21 21:55:00 发布 · 562 阅读

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#exception #gae #manager #object #query #google

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本文探讨了使用Google App Engine for Java和JDO时遇到的ObjectManagerhasbeenclosed异常问题。该问题可能发生在获取对象列表并调用size()方法之后关闭持久化管理器的情况下。通过提供一个具体的示例代码片段来说明问题，并指出移除size()调用可以避免此异常。

具体不解释：http://code.google.com/p/datanucleus-appengine/issues/detail?id=24

Root cause:
org.datanucleus.exceptions.NucleusUserException: Object Manager has been closed

Are you using Google App Engine for java and JDO?

If you ask for a list of something you might have to call the method size(). (studip i know)

The code below would throw org.datanucleus.exceptions.NucleusUserException: "Object Manager has been closed" if we removed the call to size().

public List<Customer> getAllCustomers () { List<Customer> customers = new ArrayList (); PersistenceManager pm = mfInstance.getPersistenceManager(); String query = "select from " + Customer.class.getName(); customers = ( List<Customer> pm.newQuery ( query ).execute(); customers.size(); pm.close(); return customers; }