为什么会出现“连接过多”错误

Question

我正在使用Tomcat和MySQL创建Java EE应用程序。在hibernate.cfg.xml文件中，我将连接池大小设置为10 <property name="connection.pool_size">10</property>

我还创建了一个DAO：

    public Rules getRulesById(int id) {
    Rules rules;
    factory = new Configuration().configure().buildSessionFactory();
    Session session = factory.openSession();
    try {
        Query query = session.createQuery("SELECT a FROM Rules a WHERE a.id=:id");
        query.setParameter("id", id);
        rules = (Rules) query.getSingleResult();

    } catch (Throwable ex) {
        System.err.println("Failed to create sessionFactory object." + ex);
        throw new ExceptionInInitializerError(ex);
    } finally {
        session.close();
    }

    return rules;
}

查询数据库大约30次后，出现错误：

SEVERE: Servlet.service() for servlet [Jersey Web Application] in context with path [/GoTown] threw exception [org.hibernate.service.spi.ServiceException: Unable to create requested service [org.hibernate.engine.jdbc.env.spi.JdbcEnvironment]] with root cause
java.sql.SQLNonTransientConnectionException: Data source rejected establishment of connection,  message from server: "Too many connections"

我不确定为什么，我要关闭会话：session.close（）;

谢谢！