HibernateDaoSupport 类session未关闭导致的连接泄露问题

Spring+Hibernate做项目, 发现有member在不加事务的情况下就去调用 getSession() 方法, 结果导致数据库连接不能释放, 也无法正常的提交事务(只能做查询, 不能做save(), update()). 如果配合连接池使用的话, 不出几分钟就会导致连接池无法拿到新连接的情况.

不过, 只要给DAO或者Service加入了事务, 就不会出现连接泄漏的问题.

谈谈解决方案:

最佳方案: 加入事务, 例如 tx 标签或者 @Transactional 都可以.

最笨方案: 修改代码, 使用 HibernateTemplate 来完成相关操作:

public List queryAll( final String hql, final Object… args) { List list = getHibernateTemplate().executeFind( new HibernateCallback() { public Object doInHibernate(Session session) throws HibernateException, SQLException { Query query = session.createQuery(hql); for ( int i =0; i < args. length ; i++) { query.setParameter(i, args[i]); } List list = query.list(); return list; } }); return list; } public Serializable save(Object entity) { return getHibernateTemplate().save(entity); }

但是缺陷显而易见, 要有N多的代码要进行改动.

HibernateDaoSupport 代码里面的原始说明文档指出直接调用getSession()方法必须用配套的releaseSession(Session session)来释放连接, 根据我的测试, 就算配置了 OpenSessionInViewFilter(前提: 不加事务), 也不会关闭这个Session. 也许有人说可以用连接池, 这种情况和Db pool没关系, 用了pool就会发现连接很快就会满, 只会over的更快.  反过来, 如果不配置OpenSessionInViewFilter, 在DAO里提前用 releaseSession()关闭连接, 就可能会在JSP中出现Lazy载入异常. 另一个不配事务的问题就是无法更新或者插入数据. 下面就是原始的JavaDoc中的说明:

      /** * Obtain a Hibernate Session, either from the current transaction or * a new one. The latter is only allowed if the * {@link org.springframework.orm.hibernate3.HibernateTemplate#setAllowCreate “allowCreate”} * setting of this bean’s {@link #setHibernateTemplate HibernateTemplate} is “true”. * <p><b> Note that this is not meant to be invoked from HibernateTemplate code * but rather just in plain Hibernate code. </b> Either rely on a thread – bound * Session or use it in combination with {@link #releaseSession} . * <p> In general, it is recommended to use HibernateTemplate, either with * the provided convenience operations or with a custom HibernateCallback * that provides you with a Session to work on. HibernateTemplate will care * for all resource management and for proper exception conversion. * @return the Hibernate Session * @throws DataAccessResourceFailureException if the Session couldn’t be created * @throws IllegalStateException if no thread – bound Session found and allowCreate=false * @see org.springframework.orm.hibernate3.SessionFactoryUtils#getSession(SessionFactory, boolean) */ protected final Session getSession() throws DataAccessResourceFailureException, IllegalStateException { return getSession( this . hibernateTemplate .isAllowCreate()); } /** * Close the given Hibernate Session, created via this DAO’s SessionFactory, * if it isn’t bound to the thread (i.e. isn’t a transactional Session). * <p> Typically used in plain Hibernate code, in combination with * {@link #getSession} and {@link #convertHibernateAccessException} . * @param session the Session to close * @see org.springframework.orm.hibernate3.SessionFactoryUtils#releaseSession */ protected final void releaseSession(Session session) { SessionFactoryUtils.releaseSession(session, getSessionFactory()); }

不需要改原始代码的最终方案(方案三):

不过, 如果项目里已经有了大量直接调用getSession()而且没有加入事务配置的代码(如历史原因导致), 这些代码太多, 没法一一修改, 那就最好寻求其它方案, 最好是不需要修改原来的Java代码的方案. 我采用的这第三个方案是重写 HibernateDaoSupport用ThreadLocal保存Session列表并编写一个配套的过滤器来显式关闭Session, 并在关闭之前尝试提交事务. 下面是重写的 HibernateDaoSupport 代码:

 package closesessionfiter;import java.text.SimpleDateFormat;import java.util.ArrayList;import java.util.List;import org.hibernate.HibernateException;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.springframework.dao.DataAccessException;import org.springframework.dao.DataAccessResourceFailureException;import org.springframework.dao.support.DaoSupport;import org.springframework.orm.hibernate3.HibernateTemplate;import org.springframework.orm.hibernate3.SessionFactoryUtils;/** * 修改后的避免连接泄漏的 HibernateDaoSupport, 多连接版本, 不保证跨DAO的事务. *  * @author   */public abstract class HibernateDaoSupport extends DaoSupport {/** 使用 ThreadLocal 保存打开的 Session 列表 */private static final ThreadLocal<List<Session>> sessions = new ThreadLocal<List<Session>>();/** * 获取Hibernate连接. *  * @return */public static List<Session> getSessionList() {// 1. 先看看是否有了List get()List list = sessions.get();// 2. 没有的话从创建一个, put()if (list == null) {list = new ArrayList();sessions.set(list);}// 3. 返回 Sessionreturn list;}/** * 关闭当前线程中未正常释放的 Session. */public static void closeSessionList() {// 1. 先看看是否有了List get()List<Session> list = sessions.get();// 2. 有的话就直接关闭if (list != null) {System.out.println(SimpleDateFormat.getDateTimeInstance().format(new java.util.Date())+ " -------- 即将释放未正常关闭的 Session");for (Session session : list) {System.out.println("正在关闭 session =" + session.hashCode());// ! 关闭前事务提交if (session.isOpen()) {try {session.getTransaction().commit();} catch (Exception ex) {try {session.getTransaction().rollback();} catch (HibernateException e) {// TODO Auto-generated catch block// e.printStackTrace();}}try {session.close();} catch (Exception ex) {}}// releaseSession(session); // 无法调用}sessions.remove();}}private HibernateTemplate hibernateTemplate;/** * Set the Hibernate SessionFactory to be used by this DAO. Will * automatically create a HibernateTemplate for the given SessionFactory. *  * @see #createHibernateTemplate * @see #setHibernateTemplate */public final void setSessionFactory(SessionFactory sessionFactory) {if (this.hibernateTemplate == null || sessionFactory != this.hibernateTemplate.getSessionFactory()) {this.hibernateTemplate = createHibernateTemplate(sessionFactory);}}/** * Create a HibernateTemplate for the given SessionFactory. Only invoked if * populating the DAO with a SessionFactory reference! * <p> * Can be overridden in subclasses to provide a HibernateTemplate instance * with different configuration, or a custom HibernateTemplate subclass. *  * @param sessionFactory *            the Hibernate SessionFactory to create a HibernateTemplate for * @return the new HibernateTemplate instance * @see #setSessionFactory */protected HibernateTemplate createHibernateTemplate(SessionFactory sessionFactory) {return new HibernateTemplate(sessionFactory);}/** * Return the Hibernate SessionFactory used by this DAO. */public final SessionFactory getSessionFactory() {return (this.hibernateTemplate != null ? this.hibernateTemplate.getSessionFactory() : null);}/** * Set the HibernateTemplate for this DAO explicitly, as an alternative to * specifying a SessionFactory. *  * @see #setSessionFactory */public final void setHibernateTemplate(HibernateTemplate hibernateTemplate) {this.hibernateTemplate = hibernateTemplate;}/** * Return the HibernateTemplate for this DAO, pre-initialized with the * SessionFactory or set explicitly. * <p> * <b>Note: The returned HibernateTemplate is a shared instance.</b> You * may introspect its configuration, but not modify the configuration (other * than from within an {@link #initDao} implementation). Consider creating a * custom HibernateTemplate instance via * <code>new HibernateTemplate(getSessionFactory())</code>, in which case * you're allowed to customize the settings on the resulting instance. */public final HibernateTemplate getHibernateTemplate() {return this.hibernateTemplate;}protected final void checkDaoConfig() {if (this.hibernateTemplate == null) {throw new IllegalArgumentException("'sessionFactory' or 'hibernateTemplate' is required");}}/** * Obtain a Hibernate Session, either from the current transaction or a new * one. The latter is only allowed if the * {@link org.springframework.orm.hibernate3.HibernateTemplate#setAllowCreate "allowCreate"} * setting of this bean's {@link #setHibernateTemplate HibernateTemplate} is * "true". * <p> * <b>Note that this is not meant to be invoked from HibernateTemplate code * but rather just in plain Hibernate code.</b> Either rely on a * thread-bound Session or use it in combination with * {@link #releaseSession}. * <p> * In general, it is recommended to use HibernateTemplate, either with the * provided convenience operations or with a custom HibernateCallback that * provides you with a Session to work on. HibernateTemplate will care for * all resource management and for proper exception conversion. *  * @return the Hibernate Session * @throws DataAccessResourceFailureException *             if the Session couldn't be created * @throws IllegalStateException *             if no thread-bound Session found and allowCreate=false * @see org.springframework.orm.hibernate3.SessionFactoryUtils#getSession(SessionFactory, *      boolean) */protected final Session getSession() throws DataAccessResourceFailureException, IllegalStateException {Session session = getSession(this.hibernateTemplate.isAllowCreate());// 开始事务try {session.beginTransaction();} catch (HibernateException e) {e.printStackTrace();}getSessionList().add(session);return session;}/** * Obtain a Hibernate Session, either from the current transaction or a new * one. The latter is only allowed if "allowCreate" is true. * <p> * <b>Note that this is not meant to be invoked from HibernateTemplate code * but rather just in plain Hibernate code.</b> Either rely on a * thread-bound Session or use it in combination with * {@link #releaseSession}. * <p> * In general, it is recommended to use * {@link #getHibernateTemplate() HibernateTemplate}, either with the * provided convenience operations or with a custom * {@link org.springframework.orm.hibernate3.HibernateCallback} that * provides you with a Session to work on. HibernateTemplate will care for * all resource management and for proper exception conversion. *  * @param allowCreate *            if a non-transactional Session should be created when no *            transactional Session can be found for the current thread * @return the Hibernate Session * @throws DataAccessResourceFailureException *             if the Session couldn't be created * @throws IllegalStateException *             if no thread-bound Session found and allowCreate=false * @see org.springframework.orm.hibernate3.SessionFactoryUtils#getSession(SessionFactory, *      boolean) */protected final Session getSession(boolean allowCreate) throws DataAccessResourceFailureException,IllegalStateException {return (!allowCreate ? SessionFactoryUtils.getSession(getSessionFactory(), false) : SessionFactoryUtils.getSession(getSessionFactory(), this.hibernateTemplate.getEntityInterceptor(), this.hibernateTemplate.getJdbcExceptionTranslator()));}/** * Convert the given HibernateException to an appropriate exception from the * <code>org.springframework.dao</code> hierarchy. Will automatically * detect wrapped SQLExceptions and convert them accordingly. * <p> * Delegates to the * {@link org.springframework.orm.hibernate3.HibernateTemplate#convertHibernateAccessException} * method of this DAO's HibernateTemplate. * <p> * Typically used in plain Hibernate code, in combination with * {@link #getSession} and {@link #releaseSession}. *  * @param ex *            HibernateException that occured * @return the corresponding DataAccessException instance * @see org.springframework.orm.hibernate3.SessionFactoryUtils#convertHibernateAccessException */protected final DataAccessException convertHibernateAccessException(HibernateException ex) {return this.hibernateTemplate.convertHibernateAccessException(ex);}/** * Close the given Hibernate Session, created via this DAO's SessionFactory, * if it isn't bound to the thread (i.e. isn't a transactional Session). * <p> * Typically used in plain Hibernate code, in combination with * {@link #getSession} and {@link #convertHibernateAccessException}. *  * @param session *            the Session to close * @see org.springframework.orm.hibernate3.SessionFactoryUtils#releaseSession */protected final void releaseSession(Session session) {SessionFactoryUtils.releaseSession(session, getSessionFactory());}} 

用这个类来覆盖Spring内置的那个HibernateDaoSupport, 然后随便编写一个过滤器, 如下所示:

import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;/** * @author sutk. * hibernate查询时,session不会自动关闭. * 此过滤器用来关闭session. */public class CloseSessionFilter implements Filter {public void destroy() {}public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException,ServletException { chain.doFilter(req, res); HibernateDaoSupport.closeSessionList();}public void init(FilterConfig arg0) throws ServletException {}}

 把这个过滤器配置在过滤器链的第一个,　就OK了.

 <!-- session关闭过滤器 --><filter><filter-name>sessionCloseFilter</filter-name><filter-class>closesessionfiter.CloseSessionFilter</filter-class></filter><filter-mapping><filter-name>sessionCloseFilter</filter-name><url-pattern>*.do</url-pattern></filter-mapping> 

最后也许会有人说, 为什么不用tx标签在Spring中来配置一个通配符就全部加入了事务了呢? 不过很遗憾, 经测试发现此方式无法实现跨DAO的Hibernate事务, 所以只好很无奈的放弃了这种方式.

 

配置事务管理:http://www.blogjava.net/robbie/archive/2009/04/05/264003.html

原帖:http://yhkyo.com/archives/196