hibernate设计一棵普通的树

请设计一个树型结构，完成下列需求：

1、  任意一个节点只能有一个（或0个）父节点

2、  任意一个节点可以包含多个子节点

3、  给定任意一个节点，可以输出这个节点的父节点，以及父节点的父节点，一直到顶级节点，要求输出的时候，从顶级节点开始一直输出到给定的节点为止

要求：给出实体类代码、hibernate映射文件代码以及测试代码： 

实体类:树节点：Node.java

package com.bjsxt.hibernate;
import java.util.Set;
public class Node {
               private int id;
 
              private String name;
 
              private Node parent;
 
              private Set childrens;    public int getId() {
                 return id;
             } public void setId(int id) {
               this.id = id;
          } public String getName() {
            return name;
         } public void setName(String name) {
             this.name = name;
           } public Node getParent() {
               return parent;
           } public void setParent(Node parent) {
               this.parent = parent;
           } public Set getChildrens() {
                 return childrens;
         } public void setChildrens(Set childrens) {
                this.childrens = childrens;
            } 
}

hibernate配置文件：Node.hbm.xml:

<?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>
         <class name="com.bjsxt.hibernate.Node" table="t_node">
                <id name="id">
                         <generator class="native"/>
                </id>
               <property name="name"/><!--下面为父亲节点的映射-->
              <many-to-one name="parent" column="parentid" cascade="all" /><!--下面为孩子节点的映射--->
           <set name="childrens" cascade="all" table="t_node" order-by="id">
                     <key column="parentid"></key>
                    <one-to-many class="com.bjsxt.hibernate.Node" />
           </set> 
      </class>
</hibernate-mapping>

测试NodeTest.java：

package com.bjsxt.hibernate;
import java.util.HashSet;
       import java.util.Iterator;
       import java.util.Set;import junit.framework.TestCase;
import org.hibernate.Session;
/**
 * 测试hibernate建立的普通树
 * @author Administrator
 *
 */
public class SessionTest extends TestCase {
 /**
  * 向数据库中存入数据
  */
 public void testSave1(){
        Session session = null;
 
  try{
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   Node node1 = new Node();
   node1.setName("根节点");
   
   Node node2 = new Node();
   node2.setName("节点2");
   node2.setParent(node1);
   session.save(node2);
   
   Node node3 = new Node();
   node3.setName("节点3");
   node3.setParent(node1);
   session.save(node3);
   
   Node node4 = new Node();
   node4.setName("节点4");
   node4.setParent(node1);
   session.save(node4);
   
   Node node5 = new Node();
   node5.setName("节点5");
   node5.setParent(node2);
   session.save(node5);
  
   session.getTransaction().commit();
  }catch(Exception e){
           e.printStackTrace();
            session.getTransaction().rollback();
  }finally{
           HibernateUtils.closeSession(session);
  } 
 }
 
 /**
  * 给定任意一个节点，可以输出这个节点的父节点，以及父节点的父节点，
  * 一直到顶级节点，要求输出的时候，
  * 从顶级节点开始一直输出到给定的节点为止
  */
 public void testQuery(){
  Session session = null;
  
  try{
   session = HibernateUtils.getSession();
   session.beginTransaction();
   
   Node node = (Node)session.load(Node.class, 5);
   Node parent = node.getParent();
   Set parents = new HashSet();
   while(parent != null){
    parents.add(parent);
    parent = parent.getParent();
   }
   
   for(Iterator iter = parents.iterator();iter.hasNext();){
    Node p1 = (Node)iter.next();
    System.out.println("parent：" + p1.getName());   
   }   
   session.getTransaction().commit();
  }catch(Exception e){
             e.printStackTrace();
            session.getTransaction().rollback();
  }finally{
            HibernateUtils.closeSession(session);
  }
 }
}

其中用到的包装类： HibernateUtils.java

package com.bjsxt.hibernate;
import org.hibernate.Session;
        import org.hibernate.SessionFactory;
        import org.hibernate.cfg.Configuration;public class HibernateUtils {
               private static SessionFactory factory;
 
               public HibernateUtils(){
  
               }
 
            static{
                     try{
                               Configuration cfg = new Configuration().configure();
                               factory = cfg.buildSessionFactory();
                        }catch(Exception e){
                                e.printStackTrace();
                     }
               }
 
            public static SessionFactory getSessionFactory(){
                        return factory;
            }
 
            public static Session getSession(){
                   return factory.openSession();
             }
 
          public static void closeSession(Session session){
                    if(session != null){
                              if(session.isOpen()){
                                       session.close();
                         }  
                   }
          }
}

导出数据库的工具类：ExportToDB.java

package com.bjsxt.hibernate;
import org.hibernate.cfg.Configuration;
        import org.hibernate.tool.hbm2ddl.SchemaExport;public class ExportToDB {
              public static void main(String[] aegs)throws Exception{
                      //读取配置文件
                      Configuration cfg = new Configuration().configure();
  
                      //创建SchemaExport对象
                     SchemaExport export = new SchemaExport(cfg);
  
                    //创建数据库
                    export.create(true, true);
              }
      }