Question

我正在尝试使用带有固定数据的hibernate来检索数据。但是可以在提交事务之前检索数据。提交事务后，我只能得到null个对象。这是我的Main.java代码：

package com.SSH.Action;

import java.util.HashSet;
import java.util.Set;

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

import com.SSH.Model.Address;
import com.SSH.Model.Contact;
import com.SSH.Model.Phone;

public class Main {
    private static SessionFactory factory; 
    public static void main(String args[])
    {
    try{
         factory = new     Configuration().configure().buildSessionFactory();
      }catch (Throwable ex) { 
         System.err.println("Failed to create sessionFactory object." + ex);
         throw new ExceptionInInitializerError(ex); 
      }

    Set<Phone> phoneSet = new HashSet<Phone>();
    Phone phone= new Phone();
    phone.setAreaCode(80);
    phone.setNumber(123456);
    phoneSet.add(phone);
    Address address = new Address();
    address.setCity("City");
    address.setStreet("Street");
    address.setHomeNo("12");
    Contact contact = new Contact();
    contact.setAddress(address);
    contact.setPhone(phoneSet);

    Main me = new Main();

    me.saveContact(contact);
    me.getContact();

    }

public void saveContact(Contact contact){

    Session session = factory.openSession();
    Transaction tx = null;
    try{
        tx = session.beginTransaction();
        session.save(contact);
        System.out.println(session.get(Contact.class, new Long("1")).getAddress().getCity()); // result 'City'
        tx.commit();
    }catch(HibernateException he){
        if (tx!=null) tx.rollback();
        he.printStackTrace();
    }finally {
        session.close();
    }
 }

 public void getContact(){
    Session session = factory.openSession();
    Transaction tx = null;
    try{
        tx = session.beginTransaction();
        System.out.println(session.get(Contact.class, new Long("1"))); // result 'null'
        tx.commit();
    }catch(HibernateException he){
        if (tx!=null) tx.rollback();
        he.printStackTrace();
    }finally {
        session.close(); 
    }
   }
  }

我可以在提交事务之前获取Contact对象。我应该如何从getContact方法获取该对象。当我使用这段代码时：

session.get(Contact.class, new Long("1")).list();

抛出这个Hibernate异常：

线程中的异常＆＃34; main＆＃34; java.lang.NullPointerException at org.hibernate.persister.entity.AbstractEntityPersister.loadByUniqueKey（AbstractEntityPersister.java:2159）在org.hibernate.type.EntityType.loadByUniqueKey（EntityType.java:692）在org.hibernate.type.EntityType.resolve（EntityType.java:434）at org.hibernate.engine.internal.TwoPhaseLoad.doInitializeEntity（TwoPhaseLoad.java:151）在 org.hibernate.engine.internal.TwoPhaseLoad.initializeEntity（TwoPhaseLoad.java:125）在 org.hibernate.loader.plan.exec.process.internal.AbstractRowReader.performTwoPhaseLoad（AbstractRowReader.java:238）在 org.hibernate.loader.plan.exec.process.internal.AbstractRowReader.finishUp（AbstractRowReader.java:209）在 org.hibernate.loader.plan.exec.process.internal.ResultSetProcessorImpl.extractResults（ResultSetProcessorImpl.java:133）在 org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeLoad（AbstractLoadPlanBasedLoader.java:122）在 org.hibernate.loader.plan.exec.internal.AbstractLoadPlanBasedLoader.executeLoad（AbstractLoadPlanBasedLoader.java:86）在 org.hibernate.loader.entity.plan.AbstractLoadPlanBasedEntityLoader.load（AbstractLoadPlanBasedEntityLoader.java:167）在 org.hibernate.persister.entity.AbstractEntityPersister.load（AbstractEntityPersister.java:4004）在 org.hibernate.event.internal.DefaultLoadEventListener.loadFromDatasource（DefaultLoadEventListener.java:508）在 org.hibernate.event.internal.DefaultLoadEventListener.doLoad（DefaultLoadEventListener.java:478）在 org.hibernate.event.internal.DefaultLoadEventListener.load（DefaultLoadEventListener.java:219）在 org.hibernate.event.internal.DefaultLoadEventListener.proxyOrLoad（DefaultLoadEventListener.java:278）在 org.hibernate.event.internal.DefaultLoadEventListener.doOnLoad（DefaultLoadEventListener.java:121）在 org.hibernate.event.internal.DefaultLoadEventListener.onLoad（DefaultLoadEventListener.java:89）在org.hibernate.internal.SessionImpl.fireLoad（SessionImpl.java:1213）在 org.hibernate.internal.SessionImpl.access $ 1900年（SessionImpl.java:203）在 org.hibernate.internal.SessionImpl $ IdentifierLoadAccessImpl.doLoad（SessionImpl.java:2753）在 org.hibernate.internal.SessionImpl $ IdentifierLoadAccessImpl.load（SessionImpl.java:2727）在org.hibernate.internal.SessionImpl.get（SessionImpl.java:1049）at com.SSH.Action.Main.getContact（Main.java:70）at com.SSH.Action.Main.main（Main.java:44）

检索数据时出现NullPointerException

0 个答案: