javase项目中使用hibernate如何不用重复buildSessionFactory

javase项目中使用hibernate如何不用重复buildSessionFactory,我的项目里面，每操作一次数据可靠就读取一次hibernate.cfg.xml文件，最后报一些这样的错误：
Connections could not be acquired from the underlying database!

.MySQLNonTransientConnectionException: Data source rejected establishment of connection, message from server: "Too many connections"
[b]问题补充：[/b]
谢谢yourgame ，我有几个问题想请教下
package cn.hlgc.util;

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

/**

• HibernateSession工厂
  */
  public class HibernateUtil {

  /** Hibernate的配置文件hibernate.cfg.xml /
  private static String CONFIG_FILE_LOCATION = "/hibernate.cfg.xml";
  /* Session的线程本地变量 /
  private static final ThreadLocal threadLocal = new ThreadLocal();
  /* transaction的线程本地变量 /
  private static final ThreadLocal txThreadLocal = new ThreadLocal();
  private static Configuration configuration = new Configuration();
  private static org.hibernate.SessionFactory sessionFactory;
  private static String configFile = CONFIG_FILE_LOCATION;
  [u] /*我的所有的类都继承这个类了，所以我把这个构造方法改为public了，这样做有什么坏影响吗？（这里写成私有的话，它的子类会被提示错误：Implicit super constructor HibernateUtil() is not visible. Must explicitly
  invoke another constructor）**/[/u]
  private HibernateUtil() {
  }

  /**

  • 获得一个线程本地化的Hibernate session实例
  • @return Session

  • @throws HibernateException
    */
    public static Session getSession() throws HibernateException {
    Session session = (Session) threadLocal.get();

    if (session == null || !session.isOpen()) {
    if (sessionFactory == null) {
    rebuildSessionFactory();
    }
    session = (sessionFactory != null) ? sessionFactory.openSession()
    : null;
    threadLocal.set(session);
    }

    return session;
    }

  /**

  • Rebuild hibernate session factory */ public static void rebuildSessionFactory() { try { configuration.configure(configFile); sessionFactory = configuration.buildSessionFactory(); } catch (Exception e) { System.err.println("%%%% Error Creating SessionFactory %%%%"); e.printStackTrace(); } }

  /**[size=x-large][size=large][u]还有这里什么时候关闭它呢，我的项目里免现在是用session.close()关闭一个session的，如果我一直不调用这个方法，有影响吗[/u][/size][/size]

  • 关闭线程化的Hibernate session实例

  • @throws HibernateException
    */
    public static void closeSession() throws HibernateException {
    Session session = (Session) threadLocal.get();
    threadLocal.set(null);

    if (session != null) {
    session.close();
    }
    }

  /**

  • return session factory
  • */ public static org.hibernate.SessionFactory getSessionFactory() { return sessionFactory; }

  /**

  • return session factory
  • session factory will be rebuilded in the next call */ public static void setConfigFile(String configFile) { HibernateUtil.configFile = configFile; sessionFactory = null; }

  /**

  • return hibernate configuration
  • */ public static Configuration getConfiguration() { return configuration; }

  /**

  • 在本地session实例上开启事务 */ public static void beginTransaction() { Transaction tx = (Transaction) txThreadLocal.get(); if (tx == null) { tx = getSession().beginTransaction(); txThreadLocal.set(tx); } }

  /**

  • 在本地session实例上提交事务 */ public static void commitTransaction() { Transaction tx = (Transaction) txThreadLocal.get(); if (tx != null && !tx.wasCommitted() && !tx.wasRolledBack()) { tx.commit(); txThreadLocal.set(null); } }

  /**

  • 在本地session实例上回滚事务 */ public static void rollbackTransaction() { Transaction tx = (Transaction) txThreadLocal.get(); txThreadLocal.set(null); if (tx != null && !tx.wasCommitted() && !tx.wasRolledBack()) { tx.rollback(); } }

}

[code="java"] /** * Rebuild hibernate session factory */ public synchronized static void rebuildSessionFactory() { try { configuration.configure(configFile); sessionFactory = configuration.buildSessionFactory(); } catch (Exception e) { System.err.println("%%%% 创建 SessionFactory 失败 %%%%"); e.printStackTrace(); } }

[/code]

或者这样就可以了

[code="java"]package cn.hlgc.util;

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

/**

• HibernateSession工厂
  */
  public class HibernateUtil {

  /** Hibernate的配置文件hibernate.cfg.xml /
  private static String CONFIG_FILE_LOCATION = "/hibernate.cfg.xml";
  /* Session的线程本地变量 /
  private static final ThreadLocal threadLocal = new ThreadLocal();
  /* transaction的线程本地变量 */
  private static final ThreadLocal txThreadLocal = new ThreadLocal();
  private static Configuration configuration = new Configuration();
  private static org.hibernate.SessionFactory sessionFactory;
  private static String configFile = CONFIG_FILE_LOCATION;

  private HibernateUtil() {
  }

  /**

  • 获得一个线程本地化的Hibernate session实例
  • @return Session

  • @throws HibernateException
    */
    public static Session getSession() throws HibernateException {
    Session session = (Session) threadLocal.get();

    if (session == null || !session.isOpen()) {
    if (sessionFactory == null) {
    rebuildSessionFactory();
    }
    session = (sessionFactory != null) ? sessionFactory.openSession()
    : null;
    threadLocal.set(session);
    }

    return session;
    }

  /**

  • Rebuild hibernate session factory */ public static void rebuildSessionFactory() { try { configuration.configure(configFile); sessionFactory = configuration.buildSessionFactory(); } catch (Exception e) { System.err.println("%%%% Error Creating SessionFactory %%%%"); e.printStackTrace(); } }

  /**

  • 关闭线程化的Hibernate session实例

  • @throws HibernateException
    */
    public static void closeSession() throws HibernateException {
    Session session = (Session) threadLocal.get();
    threadLocal.set(null);

    if (session != null) {
    session.close();
    }
    }

  /**

  • return session factory
  • */ public static org.hibernate.SessionFactory getSessionFactory() { return sessionFactory; }

  /**

  • return session factory
  • session factory will be rebuilded in the next call */ public static void setConfigFile(String configFile) { HibernateUtil.configFile = configFile; sessionFactory = null; }

  /**

  • return hibernate configuration
  • */ public static Configuration getConfiguration() { return configuration; }

  /**

  • 在本地session实例上开启事务 */ public static void beginTransaction() { Transaction tx = (Transaction) txThreadLocal.get(); if (tx == null) { tx = getSession().beginTransaction(); txThreadLocal.set(tx); } }

  /**

  • 在本地session实例上提交事务 */ public static void commitTransaction() { Transaction tx = (Transaction) txThreadLocal.get(); if (tx != null && !tx.wasCommitted() && !tx.wasRolledBack()) { tx.commit(); txThreadLocal.set(null); } }

  /**

  • 在本地session实例上回滚事务 */ public static void rollbackTransaction() { Transaction tx = (Transaction) txThreadLocal.get(); txThreadLocal.set(null); if (tx != null && !tx.wasCommitted() && !tx.wasRolledBack()) { tx.rollback(); } }

}[/code]

[code="java"] /** * Rebuild hibernate session factory */

public synchronized static void rebuildSessionFactory() {
try {
configuration.configure(configFile);
sessionFactory = configuration.buildSessionFactory();
} catch (Exception e) {
System.err.println("%%%% 创建 SessionFactory 失败 %%%%");
e.printStackTrace();
}
}
[/code]

一般你写在一个静态方法里面,他就只创建一次了.以后要使用你就调用静态方法就可以了

继承他做什么?他是工具类来的