Hibernate简易BaseDao演示单例模式和线程池

package com.dao;
import java.util.List;
import org.hibernate.HibernateException;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.Transaction;import org.hibernate.cfg.Configuration;
import com.IConst.IConst;
public class BaseDao {	private static Configuration cf;	private static SessionFactory sf;	/* 实例化线程池 */	private ThreadLocal<Session> thread = new ThreadLocal<Session>();
static {		init();	}
/* 	 * 单例模式 	 * */	private static synchronized void init() {		try {			if (null == cf || null == sf) {				cf = new Configuration().configure();				sf = cf.buildSessionFactory();			}		} catch (HibernateException e) {			e.printStackTrace();		}	}
/*	 * open方法	 * */	private void open() throws Exception {		/* 先从线程池中取 */		Session session = thread.get();		/* 取不到，利用工厂新建 */		if (null == session) {			session = sf.openSession();			/* 将新建的session放入线程池 */			thread.set(session);		}	}
/* 	 * close方法	 *  */	private void close() {		try {			/* 从线程池中取 */			Session session = thread.get();			/* 取到，关闭 */			if (null != session) {				session.close();				/* 清空线程池 */				thread.set(null);			}		} catch (HibernateException e) {			e.printStackTrace();		}	}
/*	 * 执行增\删\改	 * */	public boolean update(Object obj, int type) {		Session session = null;		Transaction tran = null;		try {			open();
/* 取出session */			session = thread.get();
/* 打开事务 */			tran = session.beginTransaction();			switch (type) {			case IConst.DELETE:				session.delete(obj);				break;
case IConst.INSERT:				session.save(obj);				break;
case IConst.UPDATE:				session.update(obj);				break;			}
/* Hibernate的事务机制是先将其保存在缓存中 */			/* 只有commit以后，才将事务提交 */			/* 提交事务 */			tran.commit();			return true;		} catch (Exception e) {			if (null != tran) {				tran.rollback();			}			e.printStackTrace();		} finally {			close();		}		return false;	}
/* 	 * 查询方法	 * */	public List select(String sql) {		Session session = null;		try {			open();			session = thread.get();			return session.createQuery(sql).list();		} catch (Exception e) {			e.printStackTrace();		} finally {			close();		}		return null;	}}