HibernateUtil.java

import javax.naming.InitialContext;
import javax.naming.NamingException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.hibernate.Interceptor;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.cfg.Environment;
import org.hibernate.transaction.CMTTransactionFactory;

/**
* Hibernate 工具类 用于初始化Hibernate,并进行Session和Transaction的管理
*/
public class HibernateUtil {

private static Log log = LogFactory.getLog(HibernateUtil.class);

private static final String INTERCEPTOR_CLASS = "hibernate.util.interceptor_class";

private static Configuration configuration;

private static SessionFactory sessionFactory;

private static boolean useThreadLocal = true;

// 保存Session对象实例的线程局部变量
private static ThreadLocal threadSession = new ThreadLocal();

// 保存Transaction对象实例的线程局部变量
private static ThreadLocal threadTransaction = new ThreadLocal();

static {
   try {
    // 创建Configuration对象
    configuration = new Configuration();

    // 读取hibernate.properties或者hibernate.cfg.xml文件
    configuration.configure();

    // 指定一个全局的用户子定义的拦截器
    String interceptorName = configuration
      .getProperty(INTERCEPTOR_CLASS);
    if (interceptorName != null) {
     Class interceptorClass = HibernateUtil.class.getClassLoader()
       .loadClass(interceptorName);
     Interceptor interceptor = (Interceptor) interceptorClass
       .newInstance();
     configuration.setInterceptor(interceptor);
    }

    // 如果使用CMT,那么就不使用线程安全的Session和Transaction
    if (CMTTransactionFactory.class
      .getName()
      .equals(
        configuration
          .getProperty(Environment.TRANSACTION_STRATEGY))) {
     useThreadLocal = false;
    }

    if (configuration.getProperty(Environment.SESSION_FACTORY_NAME) != null) {
     // 绑定Hibernate到JNDI
     configuration.buildSessionFactory();
    } else {
     // 使用静态的变量
     sessionFactory = configuration.buildSessionFactory();
    }
   } catch (Throwable ex) {
    // 必须捕获Throwable,否则不能捕获NoClassDefFoundError异常以及它的子类错误
    log.error("Building SessionFactory failed!", ex);
    throw new ExceptionInInitializerError(ex);
   }
}

/**
   * 返回全局的SessionFactory对象的实例
   * 
   * @return SessionFactory
   */
public static SessionFactory getSessionFactory() {
   SessionFactory sf = null;
   String sfName = configuration
     .getProperty(Environment.SESSION_FACTORY_NAME);
   if (sfName != null) {
    log.debug("Looking up SessionFactory in JNDI.");
    try {
     sf = (SessionFactory) new InitialContext().lookup(sfName);
    } catch (NamingException e) {
     throw new RuntimeException(e);
    }
   } else {
    sf = sessionFactory;
   }
   if (sf == null) {
    throw new IllegalStateException("SessionFactory not available.");
   }
   return sf;
}

/**
   * 重新构建SessionFactory对象的实例
   * 
   */
public static void rebuildSessionFactory() {
   log.debug("Using current Configuration for rebuild");
   rebuildSessionFactory(configuration);
}

/**
   * 使用指定的Configuration对象重新构建SessionFactory对象的实例
   * 
   * @param cfg
   */
public static void rebuildSessionFactory(Configuration cfg) {
   log.debug("Rebuilding the SessionFactory from given Configuration.");
   synchronized (sessionFactory) {
    if (sessionFactory != null && !sessionFactory.isClosed()) {
     sessionFactory.close();
    }
    if (cfg.getProperty(Environment.SESSION_FACTORY_NAME) != null) {
     cfg.buildSessionFactory();
    } else {
     sessionFactory = cfg.buildSessionFactory();
    }
    configuration = cfg;
   }
}

/**
   * 关闭当前SessionFactory并且释放所有资源
   * 
   */
public static void shutdown() {
   log.debug("Shutting down Hibernate.");
   // 关闭缓冲和连接池
   getSessionFactory().close();

   // 清除静态变量
   configuration = null;
   sessionFactory = null;

   // 清除本地进程变量
   threadSession.set(null);
   threadTransaction.set(null);
}

/**
   * 获得当前Session对象的实例
   * 
   * @return Session
   */
public static Session getCurrentSession() {
   if (useThreadLocal) {
    Session s = (Session) threadSession.get();
    if (s == null) {
     log.debug("Opening new Session for this thread.");
     s = getSessionFactory().openSession();
     threadSession.set(s);
    }
    return s;
   } else {
    return getSessionFactory().getCurrentSession();
   }
}

/**
   * 重新连接当前的Session
   * 
   * @param session
   */
public static void reconnect(Session session) {
   if (useThreadLocal) {
    log.debug("Reconnecting Session to this thrwad.");
    session.reconnect();
    threadSession.set(session);
   } else {
    log
      .error("Using CMT/JTA,intercepted not supported reconnect call.");
   }
}

/**
   * 断开当前Session
   * 
   * @return Session the disconnected Session
   */
public static Session disconnectedSession() {
   if (useThreadLocal) {
    Transaction tx = (Transaction) threadTransaction.get();
    if (tx != null && (!tx.wasCommitted() || !tx.wasRolledBack())) {
     throw new IllegalStateException(
       "Disconnecting Session but Transaction still open.");
    }
    Session session = getCurrentSession();
    threadSession.set(null);
    if (session.isConnected() && session.isOpen()) {
     log.debug("Disconnecting Session from this thread.");
     session.disconnect();
    }
    return session;
   } else {
    log
      .error("Using CMT/JTA,intercepted not supported disconnect call.");
    return null;
   }
}

/**
   * 关闭Session对象
   * 
   */
public static void closeSession() {
   if (useThreadLocal) {
    Session s = (Session) threadSession.get();
    threadSession.set(null);
    Transaction tx = (Transaction) threadTransaction.get();
    if (tx != null && (!tx.wasCommitted() || !tx.wasRolledBack())) {
     throw new IllegalStateException(
       "Closing Session but Transaction still open.");
    }
    if (s != null && s.isOpen()) {
     log.debug("Closing Session of this thread.");
     s.close();
    }
   } else {
    log.warn("Using CMT/JTA,intercepted superfluous close call.");
   }
}

/**
   * 开始一个新的数据库事务
   * 
   */
public static void beginTransaction() {
   if (useThreadLocal) {
    Transaction tx = (Transaction) threadTransaction.get();
    if (tx == null) {
     log.debug("Starting new database transaction in this thread.");
     tx= getCurrentSession().beginTransaction();
     threadTransaction.set(tx);
    }
   
   } else {
    log.warn("Using CMT/JTA,intercepted superfluous tx begin call.");
   }
}

/**
   * 提交数据库事务
   * 
   */
public static void commitTransaction() {
   if (useThreadLocal) {
    try {
     Transaction tx = (Transaction) threadTransaction.get();
     if (tx != null && !tx.wasCommitted() && !tx.wasRolledBack()) {
      log
        .debug("Committing database transaction of this thread.");
      tx.commit();
     }
     threadTransaction.set(null);
    } catch (RuntimeException e) {
     log.error(e);
     rollbackTransaction();
     throw e;
    }
   } else {
    log.warn("Using CMT/JTA,intercepted superfluous tx commit call.");
   }
}

/**
   * 回滚数据库事务
   * 
   */
public static void rollbackTransaction() {
   if (useThreadLocal) {

    Transaction tx = (Transaction) threadTransaction.get();
    try {
     threadTransaction.set(null);
     if (tx != null && !tx.wasCommitted() && !tx.wasRolledBack()) {
      log
        .debug("Trying to rollback database transaction of this thread.");
      tx.rollback();
     }
    } catch (RuntimeException e) {
     throw new RuntimeException(
       "Migth swallow original cause,check Error log!", e);
    } finally {
     closeSession();
    }
   } else {
    log.warn("Using CMT/JTA,intercepted superfluous tx rollback call.");
   }
}
}