Open Session In View探讨
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它有两种配置方式OpenSessionInViewInterceptor和OpenSessionInViewFilter(具体参看SpringSide),功能相同,只是一个在web.xml配置,另一个在application.xml配置而已。
Open Session In View在request把session绑定到当前thread期间一直保持hibernate session在open状态,使session在request的整个期间都可以使用,如在View层里PO也可以lazy loading数据,如 ${ company.employees }。当View 层逻辑完成后,才会通过Filter的doFilter方法或Interceptor的postHandle方法自动关闭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>
- <web-app>
- <filter>
- <filter-name>hibernateFilter</filter-name>
- <filter-class>
- org.springframework.orm.hibernate3.support.OpenSessionInViewFilter
- </filter-class>
- <!-- singleSession默认为true,若设为false则等于没用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过程中提及一个错误:
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里的几个方法
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的时候,会把获取回来的session的flush mode 设为FlushMode.NEVER。然后把该sessionFactory绑定到TransactionSynchronizationManager,使request的整个过程都使用同一个session,在请求过后再接除该sessionFactory的绑定,最后closeSessionIfNecessary根据该session是否已和transaction绑定来决定是否关闭session。在这个过程中,若HibernateTemplate 发现自当前session有不是readOnly的transaction,就会获取到FlushMode.AUTO Session,使方法拥有写权限。
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转为Flush.AUTO,拥有insert,update,delete操作权限,如果没有transaction,并且没有另外人为地设flush model的话,则doFilter的整个过程都是Flush.NEVER。所以受transaction保护的方法有写权限,没受保护的则没有。
采用spring的事务声明,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>
对于上例,则以save,add,update,remove开头的方法拥有可写的事务,如果当前有某个方法,如命名为importExcel(),则因没有transaction而没有写权限,这时若方法内有insert,update,delete操作的话,则需要手动设置flush model为Flush.AUTO,如
session.setFlushMode(FlushMode.AUTO); session.save(user); session.flush();
尽管Open Session In View看起来还不错,其实副作用不少。看回上面OpenSessionInViewFilter的doFilterInternal方法代码,这个方法实际上是被父类的doFilter调用的,因此,我们可以大约了解的OpenSessionInViewFilter调用流程: request(请求)->open session并开始transaction->controller->View(Jsp)->结束transaction并close session.
Open Session In View是个双刃剑,放在公网上内容多流量大的网站请慎用。
来源:http://calvin.blog.javascud.org/post/46.htm
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