Spring+Hibernate中(the owning Session was closed错误)

在Spring＋Hibernate中，用jUnit测试时候，提示the owning Session was closed
错误，
测试代码片段如下:
Operator operator = createOperator();
        Dept dept = createDept();
        //保存部门
        Integer deptCode = deptDao.saveDept(dept);
        Dept addDept = deptDao.getDeptByCode(deptCode);
        //保存新的用户
        operator.setDept(addDept);
        Integer userNo = operatorDao.saveOperator(operator);
        //查询用户
        Operator addOperator = operatorDao.getOperatorByCode(userNo);
        assertEquals(addOperator.getUserName(),"test");
        assertEquals(addOperator.getDept().getName(),"业务部门");
        //更新
        addOperator.setCname("其他");
        operatorDao.saveOperator(addOperator);

        Operator updateOperator = operatorDao.getOperatorByCode(userNo);
        assertEquals(updateOperator.getCname(),"其他");


        assertEquals(updateOperator.getDept().getName(),addDept.getName());
红色字体一行测试不通过，Session的生命周期结束，调用updateOperator.getDept().getName()失败。
环境：Spring2，Hibernate3，jdk1.5
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修改如下，在测试类的setUp和tearDown方法加入下代码
protected void setUp() throws Exception {
        super.setUp();
        SessionFactory sessionFactory = (SessionFactory) ctx.getBean("sessionFactory");
        session = SessionFactoryUtils.getSession(sessionFactory, true);
        TransactionSynchronizationManager.bindResource(sessionFactory, new SessionHolder(session));
    }

    protected void tearDown() throws Exception {
        super.tearDown();
        session.flush();
        SessionFactoryUtils.releaseSession(session,sessionFactory);
    }