Hibernate学习的一个问题

public class Student {



	private int id;

	private String name;

	private Date creDate;

	private List<Teacher> teachers;……}

public class Teacher {



	private int id;

	private int age;

	private String pro;

	private List<Student> students;……}

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC 

	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"

	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.test.vo">

	<class name="Teacher" table="t_teacher">

	 <id name="id">

	   <generator class="native"/>

	 </id>

	 <property name="pro" column="pro"/>

	 <property name="age" column="age"/>

	  

	

	<list name="students" table="t_teacher_student" cascade="save-update">

	<key column="t_id" not-null="true"></key>

	<index column="s_index"></index>

	<many-to-many class="Student" column="s_id"></many-to-many>

	</list>

	

	 </class>

</hibernate-mapping>

<hibernate-mapping package="com.test.vo">

	<class name="Student" table="t_student">

	 <id name="id">

	   <generator class="native"/>

	 </id>

	 <property name="name" column="sname"/>

	 <property name="creDate" column="credate" type="date"/>

 

	<list name="teachers" table="t_teacher_student" cascade="save-update">

	<key column="s_id" not-null="true"></key>

	<index column="t_index"></index>

	<many-to-many class="Teacher" column="t_id"></many-to-many>

	</list>



	 </class>

</hibernate-mapping>

public class TestSave1 extends TestCase {



	public void save1(){

		Session session=null;

		try {

			session=HibernateSessionFactory.getSession();

			session.beginTransaction();

			Student s1=new Student();

			s1.setName("s1");

			SimpleDateFormat sf=new SimpleDateFormat("yyyy-MM-dd");

			try {

				s1.setCreDate(sf.parse("1988-08-09"));

			} catch (ParseException e) {

				e.printStackTrace();

			}

  

			Student s2=new Student();

			s2.setName("s2");

			try {

				s2.setCreDate(sf.parse("1988-09-08"));

			} catch (ParseException e) {

				e.printStackTrace();

			}

			

			Teacher t1=new Teacher();

		

			List<Student> list=new ArrayList<Student>();

			list.add(s1);

			list.add(s2);

			t1.setAge(77);

			t1.setPro("computer");

			t1.setStudents(list);

		

			session.save(t1);

			session.getTransaction().commit();

		} catch (HibernateException e) {

			e.printStackTrace();

		} catch(Exception ee){

			ee.printStackTrace();

		} finally{

			HibernateSessionFactory.closeSession();

		} }