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

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#mysql #Connection refused: connect #hibernate #jdbc

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本文详细解析了MySQL数据库连接超时及Hibernate异常的问题，提供了修改my.ini配置文件的具体步骤，包括调整wait_timeout和max_connections参数，以及在Hibernate中配置自动重连的方法。

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Stacktrace:] with root cause
com.mysql.jdbc.CommunicationsException: Communications link failure due to underlying exception: 

** BEGIN NESTED EXCEPTION ** 

java.net.ConnectException
MESSAGE: Connection refused: connect

STACKTRACE:

java.net.ConnectException: Connection refused: connect
	at java.net.DualStackPlainSocketImpl.connect0(Native Method)
	at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79)
	at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
	at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
	at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
	at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
	at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
	at java.net.Socket.connect(Socket.java:579)
	at java.net.Socket.connect(Socket.java:528)
	at java.net.Socket.<init>(Socket.java:425)
	at java.net.Socket.<init>(Socket.java:241)
	at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:256)
	at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:271)
	at com.mysql.jdbc.Connection.createNewIO(Connection.java:2744)
	at com.mysql.jdbc.Connection.<init>(Connection.java:1553)
	at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285)
	at java.sql.DriverManager.getConnection(DriverManager.java:571)
	at java.sql.DriverManager.getConnection(DriverManager.java:187)
	at org.hibernate.connection.DriverManagerConnectionProvider.getConnection(DriverManagerConnectionProvider.java:110)
	at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:417)
	at org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:144)
	at org.hibernate.jdbc.AbstractBatcher.prepareQueryStatement(AbstractBatcher.java:105)
	at org.hibernate.loader.Loader.prepareQueryStatement(Loader.java:1561)
	at org.hibernate.loader.Loader.doQuery(Loader.java:661)
	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.apache.jsp.index_jsp._jspService(index_jsp.java:150)
	at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
	at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
	at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
	at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
	at bookstore.util.EncodingFilter.doFilter(EncodingFilter.java:75)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1002)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585)
	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:744)
** END NESTED EXCEPTION **

好长时间没有折腾web了，最近玩花生壳盒子把之前用的项目从内网映射到公网上面去，出现了上面异常。查询了一下，是使用了hibernate和mysql数据库连接，mysql数据库默认超时连接最长为8小时或者设置最大支持连接数过小也会导致拒绝连接（毕竟资源有限）。解决办法是修改my.ini配置文件后，重启mysql。
1、mysql5以前的版本可以直接在jdbc连接url的配置中附加上“autoReconnect=true”。
2、如果是MySQL5 以后的版本，需要修改my.cnf(或者my.ini)文件，将mysql的全局变量wait_timeout的值修改为最大。查看mysql5的手册，发现windows和linux下wait_timeout的最大值分别是24天和365天。

在文件my.ini的最后两行，单位都是秒，可通过show variables查看是否修改生效（该文件，windows下在mysql的安装目录下，linux下位置为/etc/my.ini）。

wait_timeout = 172800
interactive-timeout = 172800

修改max_connections=1000，重启mysql

最后在使用Hibernate连接数据库时，都把cfg.xml文件配置自动连接mysql，我有遇到过把mysql关掉重启，第一次访问刷新页面时，会提示org.hibernate.exception.JDBCConnectionException: Cannot open connectionweb服务器和数据库不能建立通信，原因是web服务器有缓存认为数据库挂了。
具体如何配置，可以参考Hibernate连接数据库超时设置。