Spring 的 HibernateDaoSupport 类的 getSession() 导致的连接泄露问题-白红宇

Spring 的 HibernateDaoSupport 类的 getSession() 导致的连接泄露问题

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发布时间：2019-06-25

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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. 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”.

* Note that this is not meant to be invoked from HibernateTemplate code

* but rather just in plain Hibernate code. Either rely on a thread – bound

* Session or use it in combination with {@link #releaseSession} .

* 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 DataAcce***esourceFailureException 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 DataAcce***esourceFailureException, 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).

* 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 org.springframework.orm.hibernate3.support;

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.DataAcce***esourceFailureException;

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 刘长炯

* Date: 2009-3-11

publicabstractclass HibernateDaoSupport extends DaoSupport {

/** 使用 ThreadLocal 保存打开的 Session 列表 */

privatestaticfinal ThreadLocal< List<Session> > sessions = new ThreadLocal< List<Session> >();

/**

* 获取Hibernate连接.

* @return

publicstatic 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.

publicstaticvoid 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

publicfinalvoid 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!

* 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) {

returnnew HibernateTemplate(sessionFactory);

}

/**

* Return the Hibernate SessionFactory used by this DAO.

publicfinal 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

publicfinalvoid setHibernateTemplate(HibernateTemplate hibernateTemplate) {

this.hibernateTemplate = hibernateTemplate;

}

/**

* Return the HibernateTemplate for this DAO,

* pre-initialized with the SessionFactory or set explicitly.

* Note: The returned HibernateTemplate is a shared instance.

* 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.

publicfinal HibernateTemplate getHibernateTemplate() {

returnthis.hibernateTemplate;

}

protectedfinalvoid checkDaoConfig() {

if (this.hibernateTemplate == null) {

thrownew 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".

* Note that this is not meant to be invoked from HibernateTemplate code

* but rather just in plain Hibernate code. Either rely on a thread-bound

* Session or use it in combination with {@link #releaseSession}.

* 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 DataAcce***esourceFailureException 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)

protectedfinal Session getSession()

throws DataAcce***esourceFailureException, 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.

* Note that this is not meant to be invoked from HibernateTemplate code

* but rather just in plain Hibernate code. Either rely on a thread-bound

* Session or use it in combination with {@link #releaseSession}.

* 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 DataAcce***esourceFailureException 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)

protectedfinal Session getSession(boolean allowCreate)

throws DataAcce***esourceFailureException, 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.

* Delegates to the

* {@link org.springframework.orm.hibernate3.HibernateTemplate#convertHibernateAccessException}

* method of this DAO's HibernateTemplate.

* 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

protectedfinal DataAccessException convertHibernateAccessException(HibernateException ex) {

returnthis.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).

* 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

protectedfinalvoid 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:

public void doFilter(ServletRequest req, ServletResponse res,

FilterChain chain) throws IOException, ServletException {

req.setCharacterEncoding(this.charset);

chain.doFilter(req, res);

// 关闭遗漏的 Session

HibernateDaoSupport.closeSessionList();

}把这个过滤器配置在过滤器链的第一个,　就OK了.

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. 这就是文章一开头提到的最佳方案, 也许是成本最低的方案了, 但是我却没采用, 一是因为事务问题, 二是因为每个有问题的dao/service包都要修改一次XML配置文件, 我很懒惰, 不想去看那些代码都在哪些包里面. Tx标签的配置方式如下所示:

<? xml version="1.0" encoding ="UTF-8"?>

<beansxmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:aop="http://www.springframework.org/schema/aop"

xmlns:tx="http://www.springframework.org/schema/tx"

xsi:schemaLocation="

http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd

http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.0.xsd

http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.0.xsd">

<beanid="sessionFactory"

class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">

<propertyname="configLocation"