前段时间刚完成一个家教网项目，数据库为MySQL5.0，持久层使用Hibernate 3.1，没有使用额外的连接池，那么Hibernate会默认使用它自带的一个默认连接池，也就是DriverManagerConnectionProvider。
先在本机上调试都毫无问题，于是部署到服务器上，也都没什么问题。由于这是新网站，根本还没正式对外发布和宣传，所以头两天根本没人访问。等到第二天，我再次访问网站时，问题就出现了，错误信息如下：
root cause
javax.servlet.ServletException: org.hibernate.exception.JDBCConnectionException: could not execute query
org.apache.struts.action.RequestProcessor.processException(RequestProcessor.java:535)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:433)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.apache.jsp.index_jsp._jspService(index_jsp.java:57)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:337)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
com.lab1000.jcom.system.filter.RequestEncodingFilter.doFilter(RequestEncodingFilter.java:30)
root cause
org.hibernate.exception.JDBCConnectionException: could not execute query
org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:74)
org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
org.hibernate.loader.Loader.doList(Loader.java:2148)
org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2029)
org.hibernate.loader.Loader.list(Loader.java:2024)
org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:94)
org.hibernate.impl.SessionImpl.list(SessionImpl.java:1533)
org.hibernate.impl.CriteriaImpl.list(CriteriaImpl.java:283)
com.lab1000.jcom.dao.ArticleDAO.getArticlesUnder(ArticleDAO.java:163)
com.lab1000.jcom.struts.action.HomeAction.execute(HomeAction.java:40)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.apache.jsp.index_jsp._jspService(index_jsp.java:57)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:337)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
com.lab1000.jcom.system.filter.RequestEncodingFilter.doFilter(RequestEncodingFilter.java:30)
root cause
com.mysql.jdbc.exceptions.MySQLNonTransientConnectionException: No operations allowed after connection closed.Connection was implicitly closed due to underlying exception/error:
** BEGIN NESTED EXCEPTION **
com.mysql.jdbc.CommunicationsException
MESSAGE: Communications link failure due to underlying exception:
** BEGIN NESTED EXCEPTION **
java.io.EOFException
STACKTRACE:
java.io.EOFException
at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:1963)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2375)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2874)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1623)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1715)
at com.mysql.jdbc.Connection.execSQL(Connection.java:3249)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1268)
at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:1403)
at org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:139)
at org.hibernate.loader.Loader.getResultSet(Loader.java:1669)
at org.hibernate.loader.Loader.doQuery(Loader.java:662)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:224)
at org.hibernate.loader.Loader.doList(Loader.java:2145)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2029)
at org.hibernate.loader.Loader.list(Loader.java:2024)
at org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:94)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1533)
at org.hibernate.impl.CriteriaImpl.list(CriteriaImpl.java:283)
at com.lab1000.jcom.dao.ArticleDAO.getArticlesUnder(ArticleDAO.java:163)
at com.lab1000.jcom.struts.action.HomeAction.execute(HomeAction.java:40)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:630)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:436)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)
at org.apache.jsp.index_jsp._jspService(index_jsp.java:57)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:337)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.lab1000.jcom.system.filter.RequestEncodingFilter.doFilter(RequestEncodingFilter.java:30)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:190)
at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:283)
at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:767)
at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:697)
at org.apache.jk.common.ChannelSocket$SocketConnection.runIt(ChannelSocket.java:889)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:690)
at java.lang.Thread.run(Unknown Source)
** END NESTED EXCEPTION **
Last packet sent to the server was 15 ms ago.
STACKTRACE:
com.mysql.jdbc.CommunicationsException: Communications link failure due to underlying exception:
** BEGIN NESTED EXCEPTION **
java.io.EOFException
STACKTRACE:
java.io.EOFException
at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:1963)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2375)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2874)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1623)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1715)
at com.mysql.jdbc.Connection.execSQL(Connection.java:3249)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1268)
at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:1403)
at org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:139)
at org.hibernate.loader.Loader.getResultSet(Loader.java:1669)
at org.hibernate.loader.Loader.doQuery(Loader.java:662)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:224)
at org.hibernate.loader.Loader.doList(Loader.java:2145)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2029)
at org.hibernate.loader.Loader.list(Loader.java:2024)
at org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:94)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1533)
at org.hibernate.impl.CriteriaImpl.list(CriteriaImpl.java:283)
at com.lab1000.jcom.dao.ArticleDAO.getArticlesUnder(ArticleDAO.java:163)
at com.lab1000.jcom.struts.action.HomeAction.execute(HomeAction.java:40)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:630)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:436)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)
at org.apache.jsp.index_jsp._jspService(index_jsp.java:57)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:337)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.lab1000.jcom.system.filter.RequestEncodingFilter.doFilter(RequestEncodingFilter.java:30)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:190)
at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:283)
at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:767)
at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:697)
at org.apache.jk.common.ChannelSocket$SocketConnection.runIt(ChannelSocket.java:889)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:690)
at java.lang.Thread.run(Unknown Source)
** END NESTED EXCEPTION **
Last packet sent to the server was 15 ms ago.
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2586)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2874)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1623)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1715)
at com.mysql.jdbc.Connection.execSQL(Connection.java:3249)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1268)
at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:1403)
at org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:139)
at org.hibernate.loader.Loader.getResultSet(Loader.java:1669)
at org.hibernate.loader.Loader.doQuery(Loader.java:662)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:224)
at org.hibernate.loader.Loader.doList(Loader.java:2145)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2029)
at org.hibernate.loader.Loader.list(Loader.java:2024)
at org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:94)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1533)
at org.hibernate.impl.CriteriaImpl.list(CriteriaImpl.java:283)
at com.lab1000.jcom.dao.ArticleDAO.getArticlesUnder(ArticleDAO.java:163)
at com.lab1000.jcom.struts.action.HomeAction.execute(HomeAction.java:40)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:630)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:436)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302)
at org.apache.jsp.index_jsp._jspService(index_jsp.java:57)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:337)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.lab1000.jcom.system.filter.RequestEncodingFilter.doFilter(RequestEncodingFilter.java:30)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:190)
at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:283)
at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:767)
at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:697)
at org.apache.jk.common.ChannelSocket$SocketConnection.runIt(ChannelSocket.java:889)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:690)
at java.lang.Thread.run(Unknown Source)
** END NESTED EXCEPTION **
com.mysql.jdbc.SQLError.createSQLException(SQLError.java:888)
com.mysql.jdbc.Connection.checkClosed(Connection.java:1931)
com.mysql.jdbc.Connection.prepareStatement(Connection.java:4705)
com.mysql.jdbc.Connection.prepareStatement(Connection.java:4671)
org.hibernate.jdbc.AbstractBatcher.getPreparedStatement(AbstractBatcher.java:442)
org.hibernate.jdbc.AbstractBatcher.getPreparedStatement(AbstractBatcher.java:368)
org.hibernate.jdbc.AbstractBatcher.prepareQueryStatement(AbstractBatcher.java:105)
org.hibernate.loader.Loader.prepareQueryStatement(Loader.java:1561)
org.hibernate.loader.Loader.doQuery(Loader.java:661)
org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:224)
org.hibernate.loader.Loader.doList(Loader.java:2145)
org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2029)
org.hibernate.loader.Loader.list(Loader.java:2024)
org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:94)
org.hibernate.impl.SessionImpl.list(SessionImpl.java:1533)
org.hibernate.impl.CriteriaImpl.list(CriteriaImpl.java:283)
com.lab1000.jcom.dao.ArticleDAO.getArticlesUnder(ArticleDAO.java:163)
com.lab1000.jcom.struts.action.HomeAction.execute(HomeAction.java:40)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.apache.jsp.index_jsp._jspService(index_jsp.java:57)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:337)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
com.lab1000.jcom.system.filter.RequestEncodingFilter.doFilter(RequestEncodingFilter.java:30)
当时也搞不清楚为什么，但重启Tomcat后就一切回复正常了，但是又过了一天，问题再次出现。仔细分析错误信息，问题肯定出在数据库连接部分，在网上查阅大量信息后，明确了问题的原因：MySQL对所有连接的有效时间默认为28800秒，正好8小时，也就是说，如果一个连接8小时没有请求和操作，就会自动断开；但是对于Hibernate来说，它的连接池并不知道它所管理的连接中是否有被MySQL断开的。如果一个程序要使用数据库连接，而Hibernte的连接池分配一个已经被MySQL断开了的给程序使用，那么便会出现错误。
为了证实确实是这个错误，我在本机上做了如下测试：首先启动Tomcat，网站能够正常打开；然后修改系统时间，往后调1天；然后再打开网站，同样的问题果然出现！MySQL + Hibernate架构相当普遍，所以这个问题也相当普遍，若读者也有这样的项目，建议做一下同样的测试，看看是否存在此问题！
问题找到了，怎么解决呢？
思路1：增大MySQL的连接有效时间；
思路2：从程序自身出发，修改连接池的相关参数。
显然，思路1是不可行的，一方面这个思路不可能保证这个问题绝对的解决，如果无访问时间够长，还是大于MySQL的连接有效时间，问题同样会发生；另一方面，一般情况下，我们都是将程序部署在别人服务器上，我们不可能去修改MySQL配置。那么只能从思路2入手了。
经查资料发现，Hibernate支持如下的连接池：
DriverManagerConnectionProvider：代表由Hibernate提供的默认的数据库连接池
C3P0ConnectionProvider：代表C3P0连接池
ProxoolConnectionProvider：代表Proxool连接池
DBCPConnectionProvider：代表DBCP连接池
DatasourceConnectionProvider：代表在受管理环境中由容器提供的数据源
其中，默认连接池并不支持在分配一个连接时，测试其有效与否的功能，而C3P0、Proxool、DBCP都提供了这样的功能，正好可以解决上述问题。综合考虑各个连接池的效率、稳定性、易用性，决定换用Proxool，它确实在各方面表现优良，方便配置。
下面就看看如何配置Proxool：
1、Hibernate配置文件：
<session-factory>
<property name="hibernate.connection.provider_class">org.hibernate.connection.ProxoolConnectionProvider</property>
<property name="hibernate.proxool.xml">proxool.xml</property>
<property name="hibernate.proxool.pool_alias">mysql</property>
<property name="show_sql">false</property>
<property name="dialect">org.hibernate.dialect.MySQLDialect</property>
<mapping resource="com/lab1000/jcom/pojo/Admin.hbm.xml" />
...
</session-factory>
其中各属性含义如下：
hibernate.connection.provider_class：指明使用Proxool连接池
hibernate.proxool.xml：指明Proxool配置文件所在位置，这里与Hibernate的配置文件在同一目录下
hibernate.proxool.pool_alias：指明要使用的proxool.xml中定义的proxool别名。
2、Proxool配置文件（proxool.xml）：
<?xml version="1.0" encoding="UTF-8"?>
<!-- the proxool configuration can be embedded within your own application's.
Anything outside the "proxool" tag is ignored. -->
<something-else-entirely>
<proxool>
<!-- proxool别名 -->
<alias>mysql</alias>
<!-- 数据库连接Url -->
<driver-url>
jdbc:mysql://localhost/yourDatebase?useUnicode=true&characterEncoding=UTF-8
</driver-url>
<!-- JDBC驱动名称 -->
<driver-class>com.mysql.jdbc.Driver</driver-class>
<!-- 数据库连接帐号 -->
<driver-properties>
<property name="user" value="root" />
<property name="password" value="password" />
</driver-properties>
<!-- proxool自动侦察各个连接状态的时间间隔(毫秒),侦察到空闲的连接就马上回收,超时的销毁 -->
<house-keeping-sleep-time>90000</house-keeping-sleep-time>
<!-- 指因未有空闲连接可以分配而在队列中等候的最大请求数,超过这个请求数的用户连接就不会被接受 -->
<maximum-new-connections>20</maximum-new-connections>
<!-- 最少保持的空闲连接数 -->
<prototype-count>3</prototype-count>
<!-- 允许最大连接数,超过了这个连接，再有请求时，就排在队列中等候，最大的等待请求数由maximum-new-connections决定 -->
<maximum-connection-count>20</maximum-connection-count>
<!-- 最小连接数 -->
<minimum-connection-count>3</minimum-connection-count>
<!-- 在分配连接前后是否进行有效性测试，这个是解决本问题的关键 -->
<test-before-use>true</test-before-use>
<test-after-use>true</test-after-use>
<!-- 用于测试的SQL语句 -->
<house-keeping-test-sql>SELECT CURRENT_USER</house-keeping-test-sql>
</proxool>
</something-else-entirely>
3、下载和安装Proxool的包文件
下载地址：http://proxool.sourceforge.net/download.html
下载后并解压后，将其中lib文件夹下的jar文件拷贝到你站点的WEB-INF/lib下
自此，Proxool配置成功。重新启动Tomcat，再次做上述测试，问题解决。
此外，如果要使用C3P0或DHCP，可以参考以下资料：
http://blog.csdn.net/lip8654/archive/2008/02/26/2121387.aspx
http://azi.javaeye.com/blog/182146
http://fishyych.javaeye.com/blog/90793