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

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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.

不需要改原始代码的最终方案:

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 Session
        return 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

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

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原文地址：http://my.oschina.net/tinglanrmb32/blog/359266