hibernate —— 树状存储

 package com.pt.treeStrut;

 import java.util.Set;

 import javax.persistence.CascadeType;
 import javax.persistence.Entity;
 import javax.persistence.GeneratedValue;
 import javax.persistence.Id;
 import javax.persistence.JoinColumn;
 import javax.persistence.ManyToOne;
 import javax.persistence.OneToMany;

 @Entity
 public class ArticleTree {
     int id;
     String title;
     String content;
     ArticleTree p_article;

     Set<ArticleTree> sons;

     @OneToMany(mappedBy="p_article",cascade=CascadeType.ALL)
     public Set<ArticleTree> getSons() {
         return sons;
     }

     public void setSons(Set<ArticleTree> sons) {
         this.sons = sons;
     }
     public ArticleTree(){

     }
     public ArticleTree(int id, String title, String content){
         setId(id);
         setTitle(title);
         setContent(content);
     }
     @Id
     //@GeneratedValue
     public int getId() {
         return id;
     }
     public void setId(int id) {
         this.id = id;
     }
     public String getTitle() {
         return title;
     }
     public void setTitle(String title) {
         this.title = title;
     }
     public String getContent() {
         return content;
     }
     public void setContent(String content) {
         this.content = content;
     }

     @ManyToOne(cascade=CascadeType.ALL)
     @JoinColumn(name="parent_id")
     public ArticleTree getP_article() {
         return p_article;
     }
     public void setP_article(ArticleTree p_article) {
         this.p_article = p_article;
     }

     @Override
     public String toString() {
         // TODO Auto-generated method stub
         return title + "  " + content;
     }

 }

ArticleTree.java

 import java.sql.Connection;
 import java.util.HashSet;
 import java.util.Set;

 import org.hibernate.Session;
 import org.hibernate.SessionFactory;
 import org.hibernate.cfg.Configuration;

 import com.pt.hibernate.Student;
 import com.pt.hibernate.Teacher;
 import com.pt.treeStrut.ArticleTree;

 public class Test {
     public static void main(String[] arges){
         Configuration cfg = new Configuration();
         SessionFactory factory = cfg.configure().buildSessionFactory();
         //Session ss=factory.openSession();
         Session ss= factory.getCurrentSession();
 //        Teacher hong = new Teacher();
 //        hong.setName("gaolihong");
 //        hong.setCourese("english");
 //
 //        Set<Student> students=new HashSet<Student>();
 //        Student student = new Student();
 //        student.setId(2);
 //        student.setSchoolName("DuYangGang2");
 //        students.add(student);
 //        hong.setMyStudents(students);
         ss.beginTransaction();
 //        ss.save(hong);
 //        ss.getTransaction().commit();
         ArticleTree a_p = new ArticleTree(1000,"第一章","导论");
         ArticleTree a_s1 = new ArticleTree(1001,"第一节","导论——1");
         ArticleTree a_s2 = new ArticleTree(1002,"第二节","导论——2");

         ArticleTree a_p1 = new ArticleTree(2000,"第二章","光学");
         ArticleTree a_s11 = new ArticleTree(2001,"第一节","光学——1");
         ArticleTree a_s12 = new ArticleTree(2002,"第二节","光学——2");

         a_s11.setP_article(a_p1);
         a_s12.setP_article(a_p1);
         a_p1.setSons(new HashSet<ArticleTree>());    //否则会报空指针异常
         a_p1.getSons().add(a_s11);
         a_p1.getSons().add(a_s12);

         a_s1.setP_article(a_p);
         a_s2.setP_article(a_p);
         a_p.setSons(new HashSet<ArticleTree>());
         a_p.getSons().add(a_s1);
         a_p.getSons().add(a_s2);

         ArticleTree all = new ArticleTree(1,"物理","物理");
         a_p1.setP_article(all);
         a_p.setP_article(all);
         all.setSons(new HashSet<ArticleTree>());    //否则会报空指针异常
         all.getSons().add(a_p);
         all.getSons().add(a_p1);

         //ss.save(all);    //由于设置了cascade，存储一个，整个树都会存储进去

         //ss.save(a_s1);
         ss.save(a_s1);    //由于设置了cascade，存储一个，整个树都会存储进去
         ss.getTransaction().commit();
         //ss.close();        //getsession  不用close

         /****取出树来，并打印*******/
         Session ss2= factory.getCurrentSession();
         ss2.beginTransaction();
         ArticleTree getAll = ss2.load(ArticleTree.class, 1);  //取出父节点
         printTree(getAll,0);
         ss2.getTransaction().commit();
         factory.close();
     }

     public static void printTree(ArticleTree parent,int level){
         for(int i = 0; i< level; i++){
             System.out.print("--");
         }
         System.out.println(parent);
         for(ArticleTree article : parent.getSons()){
             printTree(article, level + 1);
         }
     }
 }

test

PS:开发过程中写的bug:

　　1、commit的时候提示没有session   原因：session没有beginTransion

　　2、提示set<sons>  字段找不到匹配的数据库字段类型，  原因：@oneTomany 写在了get上