code: public static SqlSessionFactory getSessionFactory() throws IOException {
  		SqlSessionFactory sessionFactory = THREAD_SESSION_FACTORY.get();
  		try {
  			if (sessionFactory == null) {
  				sessionFactory = new DefaultSqlSessionFactory();
  				THREAD_SESSION_FACTORY.set(sessionFactory);
  			}
  		} catch (Exception e) {  
  	        throw new IOException(e);  
  	    }  
  	    return sessionFactory;  
  	}
docs: 获取当前线程的会话工厂类
  
  @return 会话工厂类
  @throws IOException IO异常处理