Spring 使用的设计模式（一） CallBack（回调）
public <T> T execute(HibernateCallback<T> action) throws DataAccessException {return doExecute(action, false, false);}protected <T> T doExecute(HibernateCallback<T> action, boolean enforceNewSession, boolean enforceNativeSession)throws DataAccessException {Assert.notNull(action, "Callback object must not be null");Session session = (enforceNewSession ?SessionFactoryUtils.getNewSession(getSessionFactory(), getEntityInterceptor()) : getSession());boolean existingTransaction = (!enforceNewSession &&(!isAllowCreate() || SessionFactoryUtils.isSessionTransactional(session, getSessionFactory())));if (existingTransaction) {logger.debug("Found thread-bound Session for HibernateTemplate");}FlushMode previousFlushMode = null;try {previousFlushMode = applyFlushMode(session, existingTransaction);enableFilters(session);Session sessionToExpose =(enforceNativeSession || isExposeNativeSession() ? session : createSessionProxy(session)); //在HibernateTemplate中得到实现，然后调用回调函数实现具体的逻辑T result = action.doInHibernate(sessionToExpose);flushIfNecessary(session, existingTransaction);return result;}catch (HibernateException ex) {throw convertHibernateAccessException(ex);}catch (SQLException ex) {throw convertJdbcAccessException(ex);}catch (RuntimeException ex) {// Callback code threw application exception...throw ex;}finally {if (existingTransaction) {logger.debug("Not closing pre-bound Hibernate Session after HibernateTemplate");disableFilters(session);if (previousFlushMode != null) {session.setFlushMode(previousFlushMode);}}else {// Never use deferred close for an explicitly new Session.if (isAlwaysUseNewSession()) {SessionFactoryUtils.closeSession(session);}else {SessionFactoryUtils.closeSessionOrRegisterDeferredClose(session, getSessionFactory());}}}}
?由此可见，在此处使用回调模式，公共部分的操作都放在了hibernateTemplate的doExcute方法里，具体的实现让程序员来实现HibernateCallback回调接口，从而实现具体的逻辑，本人感觉这是CallBack模式的一大优点
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