hibernate 连接 mysql BEGIN NESTED EXCEPTION 异常 c3p0配置解决方案（zz）

hibernate 连接 mysql BEGIN NESTED EXCEPTION 错误 c3p0配置解决方案（zz）hibernate 连接 mysql BEGIN NES

hibernate 连接 mysql BEGIN NESTED EXCEPTION 错误 c3p0配置解决方案（zz）
hibernate 连接 mysql BEGIN NESTED EXCEPTION 错误 c3p0配置解决方案（zz）新开发的一个网站，每天早上来开就有访问数据库的操作就出现异常，数据库为Mysql。也就是说在运行中每个一段长的空闲时间就出现异常，异常为:异常代码** BEGIN NESTED EXCEPTION **

com.mysql.jdbc.CommunicationsException
MESSAGE: Communications link failure due to underlying exception:

** BEGIN NESTED EXCEPTION **

java.net.SocketException
MESSAGE: Software caused connection abort: socket write error

STACKTRACE:

java.net.SocketException: Software caused connection abort: socket write error
at java.net.SocketOutputStream.socketWrite0(Native Method)
at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:92)
at java.net.SocketOutputStream.write(SocketOutputStream.java:136)
at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:65)
at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:123)
at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:2590)
at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:2523)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1517)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1626)
at com.mysql.jdbc.Connection.execSQL(Connection.java:3031)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:943)
at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:1049)
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.hql.QueryLoader.list(QueryLoader.java:375)
at org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:308)
at org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:153)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1106)
at org.hibernate.impl.QueryImpl.list(QueryImpl.java:79)
at org.hibernate.hopeDAO.StudentDBentity.findStudent(StudentDBentity.java:75)
at com.hope.student.action.StudentAction.execute(StudentAction.java:483)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:419)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:224)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1194)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
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.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
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:104)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:261)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:581)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:595)

** END NESTED EXCEPTION **

Last packet sent to the server was 1 ms ago.

STACKTRACE:

com.mysql.jdbc.CommunicationsException: Communications link failure due to underlying exception:查看了Mysql的文档，以及Connector/J的文档以及在线说明发现，出现这种异常的原因是：Mysql服务器默认的“wait_timeout”是8小时，也就是说一个connection空闲超过8个小时，Mysql将自动断开该 connection。这就是问题的所在，在C3P0 pools中的connections如果空闲超过8小时，Mysql将其断开，而C3P0并不知道该connection已经失效，如果这时有 Client请求connection，C3P0将该失效的Connection提供给Client，将会造成上面的异常。上网搜索，在MySQL的论坛上找到一个办法，就是如果在执行sql语句的时候发生了上述异常，就将sql语句重新执行一次。
试验发现，这个办法对这个使用spring+hibernate的服务无效。
进一步搜索发现，MySQL官方不推荐使用autoReconnect=true，参见http://bugs.mysql.com/bug.php?id=5020
需要另外找别的办法来解决这个问题。

由于问题产生的根本原因在于服务到数据库的连接长时间没活动，既然重新连接的办法无效，就可以尝试另外一种办法，就是反空闲。
自己写一个线程来反空闲的话，比较麻烦。
最后在网上找到一个办法。为hibernate配置连接池，推荐用c3p0，然后配置c3p0的反空闲设置idle_test_period，只要小于MySQL的wait timeout即可。
在hibernate.cfg.xml中增加下面几项：

<property name="hibernate.connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property>
<property name="c3p0.min_size">5</property>
<property name="c3p0.max_size">30</property>
<property name="c3p0.time_out">1800</property> 
<property name="c3p0.max_statement">50</property> 
<property name="c3p0.acquire_increment">1</property> 
<property name="c3p0.idle_test_period">120</property> 
<property name="c3p0.validate">true</property>

修改完后测试，问题解决。