Exception occurred during processing request: null
java.lang.NullPointerException
at sun.reflect.GeneratedMethodAccessor23.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.hibernate.property.BasicPropertyAccessor$BasicGetter.get(BasicPropertyAccessor.java:169)
at org.hibernate.tuple.entity.AbstractEntityTuplizer.getIdentifier(AbstractEntityTuplizer.java:199)
Struts,hibernate,Spring 项目，查看订单模块，启动两次服务器就可以正常运行，当又出现这种问题，再重启两次服务器，是什么原因
