求救？？？org.hibernate.TransactionException: Transaction not successfully started

在学习Hibernate
有个car的数据库，只有一个表basiccar
四个字段：
id，name，factory，date
我编写了POJO文件，也映射了，也写了Hibernate配置文件
POJO：

package basicCar.bean;



import java.util.Date;



public class BasicCar implements java.io.Serializable{

	private long id;

	private String name;

	private String factory;

	private Date date;

	public BasicCar(){

		

	}

	public BasicCar(String name,String factory,Date date){

		this.name = name;

		this.factory = factory;

		this.date = date;

	}

	public long getId() {

		return id;

	}

	public void setId(long id) {

		this.id = id;

	}

	public String getName() {

		return name;

	}

	public void setName(String name) {

		this.name = name;

	}

	public String getFactory() {

		return factory;

	}

	public void setFactory(String factory) {

		this.factory = factory;

	}

	public Date getDate() {

		return date;

	}

	public void setDate(Date date) {

		this.date = date;

	}

	

}

映射文件：

<hibernate-mapping>



<class name="basicCar.bean.BasicCar" table="basiccar">



    <id

        name="id"

        type="long"

        column="id"

    >

        <generator class="increment" />

    </id>



    <property name="name" type="java.lang.String" column="name" />

    <property name="factory" type="java.lang.String" column="factory" />

    <property name="date" type="date" column="date" />

    



</class>

</hibernate-mapping>

Hibernate；

<hibernate-configuration>



	<session-factory>

		<property name="dialect">org.hibernate.dialect.MySQLDialect</property>

		<property name="connection.driver_class">com.mysql.jdbc.Driver</property>

		<property name="connection.username">root</property>

		<property name="connection.password">1119</property> 

		<property name="connection.url">jdbc:mysql://localhost:3306/car</property>

        <property name="show_sql">true</property>

        

		<mapping resource="basicCar/bean/BasicCar.hbm.xml" />



	</session-factory>

</hibernate-configuration>

util：

package com.chuanjie56.util;



import org.hibernate.HibernateException;

import org.hibernate.Session;

import org.hibernate.cfg.Configuration;



public class HibernateSessionFactory {



    private static String CONFIG_FILE_LOCATION = "/hibernate.cfg.xml";



    @SuppressWarnings("unchecked")

	private static final ThreadLocal threadLocal = new ThreadLocal();



    private static final Configuration cfg = new Configuration();



    private static org.hibernate.SessionFactory sessionFactory;



    @SuppressWarnings("unchecked")

	public static Session currentSession() throws HibernateException {

        Session session = (Session) threadLocal.get();

        if (session == null) {

            if (sessionFactory == null) {

                try {

                    cfg.configure(CONFIG_FILE_LOCATION);

                    sessionFactory = cfg.buildSessionFactory();

                }

                catch (Exception e) {

                    System.err.println("%%%% Error Creating SessionFactory %%%%");

                    e.printStackTrace();

                }

            }

            session = sessionFactory.openSession();

            threadLocal.set(session);

        }



        return session;

    }





    @SuppressWarnings("unchecked")

	public static void closeSession() throws HibernateException {

        Session session = (Session) threadLocal.get();

        threadLocal.set(null);



        if (session != null) {

            session.close();

        }

    }



    private HibernateSessionFactory() {

    }

   

}

测试文件；

public class Test {



	/**

	 * @param args

	 */

	public static void main(String[] args) {

		// TODO Auto-generated method stub

		Test test = new Test();

		//test.saveEntity();

		test.updateEntiry();

		//test.deleteEntity();

	}

	

	void saveEntity(){

		Session session=null;

		Transaction tx = null;

		session = HibernateSessionFactory.currentSession();

		tx = session.beginTransaction();

		BasicCar bc = new BasicCar();

		bc.setFactory("Beijing123");

		bc.setName("BJcar123");

		bc.setDate(Date.valueOf("1966-02-03"));

		session.save(bc);

		tx.commit();

	}

	void deleteEntity(){

		Session session=null;

		Transaction tx = null;

		try{

			session = HibernateSessionFactory.currentSession();

			tx = session.beginTransaction();

			BasicCar bc = (BasicCar)session.load(BasicCar.class, new Long(1));

			session.delete(bc);

			tx.commit();

		}catch(HibernateException e){

			throw e;

		}finally{

			if(tx!=null)

				tx.rollback();

			HibernateSessionFactory.closeSession();

		}

	}

	void updateEntiry(){

		Session session=null;

		Transaction tx = null;

		try{

			session = HibernateSessionFactory.currentSession();

			tx = session.beginTransaction();

			BasicCar bc = (BasicCar)session.load(BasicCar.class, new Long(2));

			bc.setName("shCar");

			bc.setFactory("SH00");

			session.update(bc);

			tx.commit();

		}catch(HibernateException e){

			throw e;

		}finally{

			if(tx!=null)

				tx.rollback();

			HibernateSessionFactory.closeSession();

		}

	}

	void queryEntity(){

		Session session=null;

		try{

			session = HibernateSessionFactory.currentSession();

			Query query = session.createQuery("from BasicCar");

			BasicCar bc = (BasicCar)query.list().get(0);

			System.out.println("query:"+bc.getName());

		}catch(Exception e){

			

		}

	}

}

增加，查询操作没问题，
但是删除和更新操作报异常：
Exception in thread "main" org.hibernate.TransactionException: Transaction not successfully started
at org.hibernate.transaction.JDBCTransaction.rollback(JDBCTransaction.java:183)
at basicCar.Test.updateEntiry(Test.java:76)
at basicCar.Test.main(Test.java:27)


不知道为什么