Question

访问定义为

的字段时，我在App Engine上遇到以下异常

@Persistent(mappedBy = "shelf")
@Element(dependent = "true")
private List<ShelfData> shelfData = new ArrayList<ShelfData>();

我假设从the code看到列表中有一个空项。如何到达那里我不知道，因为我的所有插入都包含在事务中。但是，我真正想要做的是捕获错误（并忽略它，甚至删除有问题的项目）。

Uncaught exception from servlet

java.lang.NullPointerException
    at com.google.appengine.api.datastore.AsyncDatastoreServiceImpl.doBatchGetBySize(AsyncDatastoreServiceImpl.java:306)
    at com.google.appengine.api.datastore.AsyncDatastoreServiceImpl.get(AsyncDatastoreServiceImpl.java:275)
    at com.google.appengine.api.datastore.DatastoreServiceImpl$1.runInternal(DatastoreServiceImpl.java:68)
    at com.google.appengine.api.datastore.DatastoreServiceImpl$1.runInternal(DatastoreServiceImpl.java:65)
    at com.google.appengine.api.datastore.TransactionRunner.runInTransaction(TransactionRunner.java:29)
    at com.google.appengine.api.datastore.DatastoreServiceImpl.get(DatastoreServiceImpl.java:65)
    at com.google.appengine.datanucleus.WrappedDatastoreService.get(WrappedDatastoreService.java:80)
    at com.google.appengine.datanucleus.FetchFieldManager.getCollectionFromDatastoreObject(FetchFieldManager.java:666)
    at com.google.appengine.datanucleus.FetchFieldManager.fetchRelationField(FetchFieldManager.java:483)
    at com.google.appengine.datanucleus.FetchFieldManager.fetchObjectField(FetchFieldManager.java:405)
    at org.datanucleus.state.AbstractStateManager.replacingObjectField(AbstractStateManager.java:2353)
    at com.myapp.model.Shelf.jdoReplaceField(Shelf.java)
    at com.myapp.model.Shelf.jdoReplaceFields(Shelf.java)
    at org.datanucleus.state.JDOStateManager.replaceFields(JDOStateManager.java:1935)
    at org.datanucleus.state.JDOStateManager.replaceFields(JDOStateManager.java:1962)
    at com.google.appengine.datanucleus.DatastorePersistenceHandler.fetchObject(DatastorePersistenceHandler.java:567)
    at org.datanucleus.state.JDOStateManager.loadFieldsFromDatastore(JDOStateManager.java:1638)
    at org.datanucleus.state.JDOStateManager.loadSpecifiedFields(JDOStateManager.java:1240)
    at org.datanucleus.state.JDOStateManager.isLoaded(JDOStateManager.java:1728)
    at com.myapp.model.Shelf.jdoGetshelfData(Shelf.java)
    at com.myapp.model.Shelf.getShelfData(Shelf.java:137)
    ...

修复数据显然是最终的计划，但我不知道如何解决这个问题，因为一旦我访问该字段就会抛出此错误。

如何在GAE / J上使用JDO的List中键为空时捕获NPE

0 个答案: