spring＋hibernate出现未知的实体异常

下面是我写的junit方法 save方法能通过，findById就出现了未知的实体异常，怎么回事？
public void testSave(){
ApplicationContext ac;
ac=new ClassPathXmlApplicationContext("applicationContext.xml");
DeptbillDAO deptDao=(DeptbillDAO)ac.getBean("DeptbillDAO");
Deptbill dept=new Deptbill();
dept.setDetpName("销售部");
dept.setManager("程胜");
dept.setValid((byte)0);
deptDao.save(dept);
}

public void testFindById() {
ApplicationContext ac;
ac=new ClassPathXmlApplicationContext("applicationContext.xml");
DeptbillDAO deptDao=(DeptbillDAO)ac.getBean("DeptbillDAO");
System.out.println(deptDao.findById(1));
}
在默认路径 src下～
为什么第一个能通过 第二个就不能呢？

public Deptbill findById( java.lang.Integer id) {
log.debug("getting Deptbill instance with id: " + id);
try {
Deptbill instance = (Deptbill) getHibernateTe

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