持久化实体时出现NullPointerException
我成功地能够使用NamedQuery检索对象列表。 如果我不对对象进行任何修改然后尝试合并它（使用我的实体管理器），则不会抛出任何exception。 但是，如果我更新该实体中的任何字段并尝试合并它，则抛出以下exception：
SEVERE: Servlet.service() for servlet [spring-mvc] in context with path [/EuropCar] threw exception [Request processing failed; nested exception is org.springframework.transaction.TransactionSystemException: Could not commit JPA transaction; nested exception is javax.persistence.RollbackException: Error while committing the transaction] with root cause java.lang.NullPointerException at org.hibernate.ejb.event.EJB3PostUpdateEventListener.handlePostUpdate(EJB3PostUpdateEventListener.java:71) at org.hibernate.ejb.event.EJB3PostUpdateEventListener.onPostUpdate(EJB3PostUpdateEventListener.java:67) at org.hibernate.action.internal.EntityUpdateAction.postUpdate(EntityUpdateAction.java:248) at org.hibernate.action.internal.EntityUpdateAction.execute(EntityUpdateAction.java:205) at org.hibernate.engine.spi.ActionQueue.execute(ActionQueue.java:362) at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:354) at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:276) at org.hibernate.event.internal.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:328) at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:52) at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1233) at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:403) at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.beforeTransactionCommit(JdbcTransaction.java:101) at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:175) at org.hibernate.ejb.TransactionImpl.commit(TransactionImpl.java:75) at org.springframework.orm.jpa.JpaTransactionManager.doCommit(JpaTransactionManager.java:512) at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:754) at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:723) at org.springframework.transaction.interceptor.TransactionAspectSupport.commitTransactionAfterReturning(TransactionAspectSupport.java:393) at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:120) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172) at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202) 我检查了以下内容：
- 我坚持的实体不是空的。
- entityManager不为null。
任何帮助将不胜感激。
// Code to update the 'Rate' entity Rate r = rateDao.getRate(); r.setCountry("NA"); rateDao.update(r); // RateDaoImpl code (DAO IMPLEMENTATION CLASS) @Override public Rate getRate() { // named query is : "SELECT rp FROM RatePeriod rp WHERE rp.id = 458" return em.createNamedQuery("Rate.qry", Rate.class).getResultList().get(0); } @Transactional(readOnly=false) @Override public void update(Rate rate) { em.merge(rate); }
我在同一行中有同样的例外。 那是因为我使用了不兼容的版本：hibernate-core：4.2.0.Final hibernate-entitymanager：4.1.9.Final
我已将hibernate-core降级为4.1.9.Final并且问题消失了。
这是EJB3PostUpdateEventListener的代码：
70 private void handlePostUpdate(Object entity, EventSource source) { 71 EntityEntry entry = (EntityEntry) source.getPersistenceContext().getEntry( entity ); 72 // mimic the preUpdate filter 73 if ( Status.DELETED != entry.getStatus()) { 74 callbackHandler.postUpdate(entity); 75 } 76 }
在此方法中设置断点并查看什么是null行71.也许getPersistenceContext()返回null 。