Question

我想使用hql或jpql在两个不同的数据库（两个不同数据库引擎和相同供应商）上的两个表上编写查询？数据库A中的tblA mysql ServerA 数据库B中的 mysql ServerB上的tblB 有什么解决方案？

Answer 1

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

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

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）？

1 个答案: