应用myeclipse生成的HibernateSessionFactory的合理性

使用myeclipse生成的HibernateSessionFactory的合理性
作为简单的一个单件模式，
getSessionFactory()函数返回null是一个不合理的决定，可以返回一个没有初始化的SessionFactory对象，但是返回null就和这种模式的语意有冲突了。

以下是用myeclipse5自动生成的代码：

package model.sessionfatory;
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 threadLocal = new ThreadLocal();
    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;
}
}

里边的这个函数：
/**
     *  return session factory
     *
     */
public static org.hibernate.SessionFactory getSessionFactory() {
  return sessionFactory;
}

是否应该修改为：
/**
     *  return session factory
     *
     */
public static org.hibernate.SessionFactory getSessionFactory() {
  rebuildSessionFactory();
  return sessionFactory;
}

这样调用代码：
  dao.setSessionFactory(HibernateSessionFactory.getSessionFactory());
会报错误：
java.lang.IllegalArgumentException: sessionFactory is required
at org.springframework.orm.hibernate3.HibernateAccessor.afterPropertiesSet(HibernateAccessor.java:318)
at org.springframework.orm.hibernate3.HibernateTemplate.<init>(HibernateTemplate.java:147)
at org.springframework.orm.hibernate3.support.HibernateDaoSupport.createHibernateTemplate(HibernateDaoSupport.java:83)
at org.springframework.orm.hibernate3.support.HibernateDaoSupport.setSessionFactory(HibernateDaoSupport.java:70)
at test.TestOrgTypeDAO.testFindById(TestOrgTypeDAO.java:66)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at junit.framework.TestCase.runTest(TestCase.java:154)
at junit.framework.TestCase.runBare(TestCase.java:127)
at junit.framework.TestResult$1.protect(TestResult.java:106)
at junit.framework.TestResult.runProtected(TestResult.java:124)
at junit.framework.TestResult.run(TestResult.java:109)
at junit.framework.TestCase.run(TestCase.java:118)
at junit.framework.TestSuite.runTest(TestSuite.java:208)
at junit.framework.TestSuite.run(TestSuite.java:203)
at org.eclipse.jdt.internal.junit.runner.junit3.JUnit3TestReference.run(JUnit3TestReference.java:128)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:460)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:673)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:386)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:196)

而这样调用却不会错误：
  HibernateSessionFactory.rebuildSessionFactory();
  dao.setSessionFactory(HibernateSessionFactory.getSessionFactory());