HibernateSssionFactory 辅助工具类，既负责Hibernate的启动，也负责完成存储和访问SessionFactory的工作

HibernateSessionFactory.java

package cn.it.shop.util;

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

/*Hibernate：辅助工具类，既负责Hibernate的启动，也负责完成存储和访问SessionFactory的工作。
 * 使用Hibernate类来处理java应用程序中的Hibernate的启动是一种常见的模式
 */
public class HibernateSessionFactory {
    private static SessionFactory sessionfactory;
    // 创建线程局部变量threadLocal,用来保存Hibernate中的Session
    private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();
    // 使用静态代码块来初始化Hibernate
    static {
        try {
            Configuration cfg = new Configuration().configure("/hibernate.cfg.xml");// 读取配置文件hibernate.cfg.xml
            sessionfactory = cfg.buildSessionFactory(); // 创建SessionFactory
        } catch (Throwable ex) {
            throw new ExceptionInInitializerError(ex);
        }
    }

    // 获得SessionFactory的实例
    public static SessionFactory getSessionFactory() {
        return sessionfactory;
    }

    // 获得ThreadLocal对象管理的Session实例
    public static Session getSession() throws HibernateException {
        Session session = (Session) threadLocal.get();
        if (session == null || !session.isOpen()) {
            // 通过sessionfactory创建session
            if (sessionfactory == null) {
                rebuildSessionFactory();
            }
            session = (sessionfactory != null) ? sessionfactory.openSession()
                    : null;
            threadLocal.set(session);
        }
        return session;
    }

    // 关闭Session实例
    public static void closeSession() throws HibernateException {
        Session session = threadLocal.get();
        threadLocal.set(null);
        if (session != null) {
            session.close();
        }
    }

    // 关闭缓存和连接池
    public static void shutdown() {
        sessionfactory = getSessionFactory();
        if (sessionfactory != null) {
            sessionfactory.close();
        }
    }

    // 重建SessionFactory
    private static void rebuildSessionFactory() {
        try {
            Configuration cfg = new Configuration()
                    .configure("/HibernateConf/hibernate.cfg.xml");
            sessionfactory = cfg.buildSessionFactory();
        } catch (Exception e) {
            System.out.println("SessionFactory build error");
            e.printStackTrace();
        }

    }

}