java – 如何在hql或jpql查询中查询两个不同的数据库(在不同的服务器上)？

我想使用hql或jpql在两个不同的数据库(在具有相同供应商的两个不同的数据库引擎)上的两个表上编写查询？ mysql ServerA上的databaseA中的tblA mysql ServerB上的databaseB中的tblB有什么解决方案？解决方法:基...

我想使用hql或jpql在两个不同的数据库(在具有相同供应商的两个不同的数据库引擎)上的两个表上编写查询？
     mysql ServerA上的databaseA中的tblA
    mysql ServerB上的databaseB中的tblB
有什么解决方案？

解决方法:

基本上你必须得到两个会话工厂 – 每个数据库一个(数据源).我找到了以下代码：http://www.java-forums.org/jdbc/867-hibernate-multiple-databases.html应该可以解决这个问题.

public class HibernateUtil {

    private static Log log = LogFactory.getLog(HibernateUtil.class);
    private static HashMap<String, SessionFactory> sessionFactoryMap = new HashMap<String, SessionFactory>();

    public static final ThreadLocal sessionMapsThreadLocal = new ThreadLocal();

    public static Session currentSession(String key) throws HibernateException {

        HashMap<String, Session> sessionMaps = (HashMap<String, Session>) sessionMapsThreadLocal.get();

        if (sessionMaps == null) {
            sessionMaps = new HashMap();
            sessionMapsThreadLocal.set(sessionMaps);
        }

        // Open a new Session, if this Thread has none yet
        Session s = (Session) sessionMaps.get(key);
        if (s == null) {
            s = ((SessionFactory) sessionFactoryMap.get(key)).openSession();
            sessionMaps.put(key, s);
        }

        return s;
    }

    public static Session currentSession() throws HibernateException {
        return currentSession("");
    }

    public static void closeSessions() throws HibernateException {
        HashMap<String, Session> sessionMaps = (HashMap<String, Session>) sessionMapsThreadLocal.get();
        sessionMapsThreadLocal.set(null);
        if (sessionMaps != null) {
            for (Session session : sessionMaps.values()) {
                if (session.isOpen())
                    session.close();
            };
        }
    }

    public static void closeSession() {
        HashMap<String, Session> sessionMaps = (HashMap<String, Session>) sessionMapsThreadLocal.get();
        sessionMapsThreadLocal.set(null);
        if (sessionMaps != null) {
            Session session = sessionMaps.get("");
            if (session != null && session.isOpen())
                session.close();
        }
    }

    public static void buildSessionFactories(HashMap<String, String> configs) {
        try {
            // Create the SessionFactory
            for (String key : configs.keySet()) {
                URL url = HibernateUtil.class.getResource(configs.get(key));
                SessionFactory sessionFactory = new Configuration().configure(url).buildSessionFactory();
                sessionFactoryMap.put(key, sessionFactory);
            }

        } catch (Exception ex) {
            ex.printStackTrace(System.out);
            log.error("Initial SessionFactory creation failed.", ex);
            throw new ExceptionInInitializerError(ex);

        } // end of the try - catch block
    }

    public static void buildSessionFactory(String key, String path) {
        try {
            // Create the SessionFactory
            URL url = HibernateUtil.class.getResource(path);
            SessionFactory sessionFactory = new Configuration().configure(url).buildSessionFactory();
            sessionFactoryMap.put(key, sessionFactory);

        } catch (Throwable ex) {

            log.error("Initial SessionFactory creation failed.", ex);
            throw new ExceptionInInitializerError(ex);

        } // end of the try - catch block
    }

} // end of the class