1.模型
一个用户拥有多个角色，一个角色拥有多个用户。
2.实体类（省略set，get方法）
public  class User { 
private  int id; 
private String name; 
private Set roles; 
}

public  class Role { 
private  int id; 
private String name; 
private Set users; 
}

3.数据模型
mysql> desc t_user;
+-------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(255) | YES | | NULL | |
+-------+--------------+------+-----+---------+----------------+
mysql> desc t_role;
+-------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(255) | YES | | NULL | |
+-------+--------------+------+-----+---------+----------------+
4.映射文件
User.hbm.xml
< hibernate-mapping > 
< class  name ="com.bjsxt.hibernate.User"  table ="t_user" > 
< id  name ="id" > 
< generator  class ="native" /> 
</ id > 
< property  name ="name" /> 
< set  name ="roles"  table ="t_user_role" > 
< key  column ="userid" /> 
< many-to-many  class ="com.bjsxt.hibernate.Role"  column ="roleid" /> 
</ set > 
</ class > 
</ hibernate-mapping > 
Role.hbm.xml
< hibernate-mapping > 
< class  name ="com.bjsxt.hibernate.Role"  table ="t_role" > 
< id  name ="id" > 
< generator  class ="native" /> 
</ id > 
< property  name ="name" /> 
< set  name ="users"  table ="t_user_role" > 
< key  column ="roleid" /> 
< many-to-many  class ="com.bjsxt.hibernate.User"  column ="userid" /> 
</ set > 
</ class > 
</ hibernate-mapping > 
<key>中的column属性值必须等于单向关联中<many-to-many>标签指向的column的属性值
<many-to-many>中column属性值必须等于单向关联中<key>中column的属性值
5.测试
public  class ManyToManyTest  extends TestCase { 
//存储 
public  void testSave(){ 
Session session = HibernateUtils.getSession(); 
Transaction tx = session.beginTransaction(); 
User user1 =  new User(); 
user1.setName( "yang9"); 
session.save(user1); 
User user2 =  new User(); 
user2.setName( "long1"); 
session.save(user2); 
Set<User> users =  new HashSet<User>(); 
users.add(user1); 
users.add(user2); 
Role role1 =  new Role(); 
role1.setName( "凤山人在线"); 
role1.setUsers(users); 
session.save(role1); 
tx.commit(); 
} 
//导入 
public  void testLoad(){ 
Session session =HibernateUtils.getSession(); 
Transaction tx = session.beginTransaction(); 
Role role = (Role) session.load(Role. class, 1); 
System.out.println(role.getName()); 
for(Iterator ite=role.getUsers().iterator();ite.hasNext();){ 
User user = (User) ite.next(); 
System.out.println(user.getName()); 
} 
}