open session in view 的使用
Posted on 2008-03-28 20:29 hilor 閱讀(1043) 評(píng)論(0) 編輯 收藏 所屬分類: Spring 、Hibernate它有兩種配置方式OpenSessionInViewInterceptor和OpenSessionInViewFilter(具體參看SpringSide),功能相同,只是一個(gè)在web.xml配置,另一個(gè)在application.xml配置而已。
Open Session In View在request把session綁定到當(dāng)前thread期間一直保持hibernate session在open狀態(tài),使session在request的整個(gè)期間都可以使用,如在View層里PO也可以lazy loading數(shù)據(jù),如 ${ company.employees }。當(dāng)View 層邏輯完成后,才會(huì)通過(guò)Filter的doFilter方法或Interceptor的postHandle方法自動(dòng)關(guān)閉session。
OpenSessionInViewInterceptor配置
<beans> <bean name="openSessionInViewInterceptor" class="org.springframework.orm.hibernate3.support.OpenSessionInViewInterceptor"> <property name="sessionFactory"> <ref bean="sessionFactory"/> </property> </bean> <bean id="urlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping"> <property name="interceptors"> <list> <ref bean="openSessionInViewInterceptor"/> </list> </property> <property name="mappings"> ... </property> </bean> ... </beans>
OpenSessionInViewFilter配置
<web-app> ... <filter> <filter-name>hibernateFilter</filter-name> <filter-class> org.springframework.orm.hibernate3.support.OpenSessionInViewFilter </filter-class> <!-- singleSession默認(rèn)為true,若設(shè)為false則等于沒(méi)用OpenSessionInView --> <init-param> <param-name>singleSession</param-name> <param-value>true</param-value> </init-param> </filter> ... <filter-mapping> <filter-name>hibernateFilter</filter-name> <url-pattern>*.do</url-pattern> </filter-mapping> ... </web-app>
很多人在使用OpenSessionInView過(guò)程中提及一個(gè)錯(cuò)誤:
org.springframework.dao.InvalidDataAccessApiUsageException: Write operations are not allowed in read-only mode (FlushMode.NEVER) - turn your Session into FlushMode.AUTO or remove 'readOnly' marker from transaction definition
看看OpenSessionInViewFilter里的幾個(gè)方法
protected void doFilterInternal(HttpServletRequest request,
HttpServletResponse response,FilterChain filterChain)
throws ServletException, IOException {
SessionFactory sessionFactory = lookupSessionFactory();
logger.debug("Opening Hibernate Session in OpenSessionInViewFilter");
Session session = getSession(sessionFactory);
TransactionSynchronizationManager.bindResource(
sessionFactory, new SessionHolder(session));
try {
filterChain.doFilter(request, response);
}
finally {
TransactionSynchronizationManager.unbindResource(sessionFactory);
logger.debug("Closing Hibernate Session in OpenSessionInViewFilter");
closeSession(session, sessionFactory);
}
}
protected Session getSession(SessionFactory sessionFactory)
throws DataAccessResourceFailureException {
Session session = SessionFactoryUtils.getSession(sessionFactory, true);
session.setFlushMode(FlushMode.NEVER);
return session;
}
protected void closeSession(Session session, SessionFactory sessionFactory)
throws CleanupFailureDataAccessException {
SessionFactoryUtils.closeSessionIfNecessary(session, sessionFactory);
}
可以看到OpenSessionInViewFilter在getSession的時(shí)候,會(huì)把獲取回來(lái)的session的flush mode 設(shè)為FlushMode.NEVER。然后把該sessionFactory綁定到 TransactionSynchronizationManager,使request的整個(gè)過(guò)程都使用同一個(gè)session,在請(qǐng)求過(guò)后再接除該 sessionFactory的綁定,最后closeSessionIfNecessary根據(jù)該 session是否已和transaction綁定來(lái)決定是否關(guān)閉session。在這個(gè)過(guò)程中,若HibernateTemplate 發(fā)現(xiàn)自當(dāng)前session有不是readOnly的transaction,就會(huì)獲取到FlushMode.AUTO Session,使方法擁有寫權(quán)限。
public static void closeSessionIfNecessary(Session session, SessionFactory sessionFactory) throws CleanupFailureDataAccessException { if (session == null ||
TransactionSynchronizationManager.hasResource(sessionFactory)) { return; } logger.debug("Closing Hibernate session"); try { session.close(); } catch (JDBCException ex) { // SQLException underneath throw new CleanupFailureDataAccessException("Could not close Hibernate session", ex.getSQLException()); } catch (HibernateException ex) { throw new CleanupFailureDataAccessException("Could not close Hibernate session", ex); } }
也即是,如果有不是readOnly的transaction就可以由Flush.NEVER轉(zhuǎn)為Flush.AUTO,擁有insert, update,delete操作權(quán)限,如果沒(méi)有transaction,并且沒(méi)有另外人為地設(shè)flush model的話,則doFilter的整個(gè)過(guò)程都是Flush.NEVER。所以受transaction保護(hù)的方法有寫權(quán)限,沒(méi)受保護(hù)的則沒(méi)有。
采用spring的事務(wù)聲明,使方法受transaction控制
<bean id="baseTransaction"
class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean"
abstract="true">
<property name="transactionManager" ref="transactionManager"/>
<property name="proxyTargetClass" value="true"/>
<property name="transactionAttributes">
<props>
<prop key="get*">PROPAGATION_REQUIRED,readOnly</prop>
<prop key="find*">PROPAGATION_REQUIRED,readOnly</prop>
<prop key="load*">PROPAGATION_REQUIRED,readOnly</prop>
<prop key="save*">PROPAGATION_REQUIRED</prop>
<prop key="add*">PROPAGATION_REQUIRED</prop>
<prop key="update*">PROPAGATION_REQUIRED</prop>
<prop key="remove*">PROPAGATION_REQUIRED</prop>
</props>
</property>
</bean>
- <bean id="userService" parent="baseTransaction">
<property name="target">
<bean class="com.phopesoft.security.service.impl.UserServiceImpl"/>
</property>
</bean>
對(duì) 于上例,則以save,add,update,remove開頭的方法擁有可寫的事務(wù),如果當(dāng)前有某個(gè)方法,如命名為importExcel(),則因沒(méi) 有transaction而沒(méi)有寫權(quán)限,這時(shí)若方法內(nèi)有insert,update,delete操作的話,則需要手動(dòng)設(shè)置flush model為Flush.AUTO,如
session.setFlushMode(FlushMode.AUTO); session.save(user); session.flush();
盡管Open Session In View看起來(lái)還不錯(cuò),其實(shí)副作用不少。看回上面OpenSessionInViewFilter的doFilterInternal方法代碼,這個(gè)方法 實(shí)際上是被父類的doFilter調(diào)用的,因此,我們可以大約了解的OpenSessionInViewFilter調(diào)用流程: request(請(qǐng)求)->open session并開始transaction->controller->View(Jsp)->結(jié)束transaction并 close session.
一切看起來(lái)很正確,尤其是在本地開發(fā)測(cè)試的時(shí)候沒(méi)出現(xiàn)問(wèn)題,但試想下如果流程中的某一步被阻塞的話,那在這期間connection就一直被占用而不釋 放。最有可能被阻塞的就是在寫Jsp這步,一方面可能是頁(yè)面內(nèi)容大,response.write的時(shí)間長(zhǎng),另一方面可能是網(wǎng)速慢,服務(wù)器與用戶間傳輸時(shí) 間久。當(dāng)大量這樣的情況出現(xiàn)時(shí),就有連接池連接不足,造成頁(yè)面假死現(xiàn)象。
Open Session In View是個(gè)雙刃劍,放在公網(wǎng)上內(nèi)容多流量大的網(wǎng)站請(qǐng)慎用。
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