OpenSessionInViewFilter配置
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<web-app>
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...
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<filter>
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<filter-name>hibernateFilter</filter-name>
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<filter-class>
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org.springframework.orm.hibernate3.support.OpenSessionInViewFilter
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</filter-class>
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<!-- singleSession默認(rèn)為true,若設(shè)為false則等于沒(méi)用OpenSessionInView -->
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<init-param>
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<param-name>singleSession</param-name>
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<param-value>true</param-value>
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</init-param>
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</filter>
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...
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<filter-mapping>
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<filter-name>hibernateFilter</filter-name>
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<url-pattern>*.do</url-pattern>
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</filter-mapping>
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...
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</web-app>
很多人在使用OpenSessionInView過(guò)程中提及一個(gè)錯(cuò)誤：
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org.springframework.dao.InvalidDataAccessApiUsageException: Write operations
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are not allowed in read-only mode (FlushMode.NEVER) - turn your Session into
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FlushMode.AUTO or remove 'readOnly' marker from transaction definition
看看OpenSessionInViewFilter里的幾個(gè)方法
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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);
}
}
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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(xiě)權(quán)限。
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public static void closeSessionIfNecessary(Session session, SessionFactory sessionFactory)
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throws CleanupFailureDataAccessException {
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if (session == null ||
TransactionSynchronizationManager.hasResource(sessionFactory)) {
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return;
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}
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logger.debug("Closing Hibernate session");
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try {
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session.close();
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}
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catch (JDBCException ex) {
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// SQLException underneath
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throw new CleanupFailureDataAccessException("Could not close Hibernate session", ex.getSQLException());
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}
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catch (HibernateException ex) {
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throw new CleanupFailureDataAccessException("Could not close Hibernate session", ex);
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}
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}
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(xiě)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
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<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(kāi)頭的方法擁有可寫(xiě)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(xiě)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
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session.setFlushMode(FlushMode.AUTO);
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session.save(user);
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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(lèi)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(kāi)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(kāi)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(xiě)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。