问题在休眠DAO（会话已经关闭!!） [英] problem in hibernate DAO (session already closed!!)

问题描述

我已经实现了DAO，如下所示，

//伪代码

  public MyDAO {
 
 private session session; 
 MYDAO {
 this.setSession（HibernateUtil.getSessionFactory（）。getCurrentSession（））; 
} 
 
 public void save（MyObj obj）{
 // save obj in db 
} 
} 
  
 
  EG 
 特征特征=新特征）; 
 feature.setFeatureName（testf333）; 
 
 FeatureDAO featureDAO = new FeatureDAO（）; 
 Transaction tx = featureDAO.getSession（）。beginTransaction（）; 
 featureDAO.makePersistent（feature）; 
 tx.commit（）; 
 System.out.println（成功保存在数据库中+ feature.getId（））; 
 
 
 tx = featureDAO.getSession（）。beginTransaction（）; //在这里获取错误
 Feature feature4 = new Feature（）; 
 feature4.setFeatureName（4444）; 
 featureDAO.makePersistent（feature4）; 
 
 tx.commit（）; 
 System.out.println（成功保存在数据库中+ feature.getId（））; 
  
我认为这个问题可以通过检查session是否关闭来解决。但是我可以在哪里设置一个新的会话，因为我使用DAO的会话来启动一个transcation 
解决方案
与其试图坚持 Session 在你的 MyDAO 中，你可能最好只保留 SessionFactory ，通过在 MyDAO 中定义您的 getSession 方法作为
  public Session getSession（）{
 return sessionFactory.getCurrentSession（）; 
 
 $ / code> 
或者只保存与 MyDao中的会话处理相关的任何内容在所有和使用
  public Session getSession（）{
 return HibernateUtil.getSessionFactory ）.getCurrentSession（）; 
 
  
 hibernate会话绑定到特定的线程，并在提交时关闭，但会话工厂的 getCurrentSession（）方法根据需要获取新会话，以便您不必担心。
 
I have implemented DAO as  follows,

//pseudoCode
public MyDAO{

  private Session session;
  MYDAO{
  this.setSession(HibernateUtil.getSessionFactory().getCurrentSession());
  }

  public void save(MyObj obj){
   //save obj in db
  }
}
Now i have used the dao to save a single object it works fine.Now if save two object inside seperate transcation i get a error saying "session is already closed"

EG
Feature feature = new Feature();
feature.setFeatureName("testf333");

FeatureDAO featureDAO = new FeatureDAO();
Transaction tx = featureDAO.getSession().beginTransaction();
featureDAO.makePersistent(feature);
tx.commit();
System.out.println("successfully save in db " + feature.getId());


tx = featureDAO.getSession().beginTransaction();  //getting error here
Feature feature4 = new Feature();
feature4.setFeatureName("4444");
featureDAO.makePersistent(feature4);

tx.commit();
System.out.println("successfully save in db " + feature.getId());
I think this problem can be solved by checking if session is closed .But where can i set a new session because i use the session from DAO to start a transcation
解决方案
Rather than trying to hold onto the Session in your MyDAO, you're probably best off holding onto just the SessionFactory, and getting a session from is when needed, by defining your getSession method in MyDAO as
public Session getSession() {
   return sessionFactory.getCurrentSession();
}
or just save nothing related to session handling in MyDao at all and use
public Session getSession() {
   return HibernateUtil.getSessionFactory().getCurrentSession();
}
A hibernate session is tied to a specific thread and closed on commit, but the session factory's getCurrentSession() method gets a new session as needed so that you don't have to worry about it.

                        
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