hinernate

    多个进程第一次进来调用HibernateSessionFactory 的getSession() 会报错，原因是多次调用rebuildSessionFactory。建议在启动服务是首先ebuildSessionFactory。
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.cfg.Configuration;

/**
* Configures and provides access to Hibernate sessions, tied to the
* current thread of execution.  Follows the Thread Local Session
* pattern, see {@link http://hibernate.org/42.html }.
*/
public class HibernateSessionFactory {

    /**
     * Location of hibernate.cfg.xml file.
     * Location should be on the classpath as Hibernate uses 
     * #resourceAsStream style lookup for its configuration file.
     * The default classpath location of the hibernate config file is
     * in the default package. Use #setConfigFile() to update
     * the location of the configuration file for the current session.  
     */
    private static String CONFIG_FILE_LOCATION = "/hibernate.cfg.xml";
private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();
    private  static Configuration configuration = new Configuration();
    private static org.hibernate.SessionFactory sessionFactory;
    private static String configFile = CONFIG_FILE_LOCATION;

    private HibernateSessionFactory() {
    }

/**
     * Returns the ThreadLocal Session instance.  Lazy initialize
     * the <code>SessionFactory</code> if needed.
     *
     *  @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();
}
}

/**
     *  Close the single hibernate session instance.
     *
     *  @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) {
HibernateSessionFactory.configFile = configFile;
sessionFactory = null;
}

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

}