本文主要是介绍记录一次Communications link failure due to underlying exception connect异常定位，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
长时间未启动项目，再次启动的时候报错：
org.apache.tomcat.dbcp.dbcp.SQLNestedException: Cannot create PoolableConnectionFactory (Communications link failure due to underlying exception:
** BEGIN NESTED EXCEPTION **
java.net.ConnectException
MESSAGE: Connection timed out: connect
STACKTRACE:
java.net.ConnectException: Connection timed out: connect
at java.net.DualStackPlainSocketImpl.connect0(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at java.net.Socket.connect(Socket.java:538)
at java.net.Socket.<init>(Socket.java:434)
at java.net.Socket.<init>(Socket.java:244)
at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:173)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:267)
at com.mysql.jdbc.Connection.createNewIO(Connection.java:2739)
at com.mysql.jdbc.Connection.<init>(Connection.java:1553)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:266)
at org.apache.tomcat.dbcp.dbcp.DriverConnectionFactory.createConnection(DriverConnectionFactory.java:38)
at org.apache.tomcat.dbcp.dbcp.PoolableConnectionFactory.makeObject(PoolableConnectionFactory.java:582)
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.validateConnectionFactory(BasicDataSource.java:1556)
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createPoolableConnectionFactory(BasicDataSource.java:1545)
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:1388)
at org.apache.tomcat.dbcp.dbcp.BasicDataSource.getLogWriter(BasicDataSource.java:1098)
at org.apache.tomcat.dbcp.dbcp.BasicDataSourceFactory.createDataSource(BasicDataSourceFactory.java:350)
at org.apache.tomcat.dbcp.dbcp.BasicDataSourceFactory.getObjectInstance(BasicDataSourceFactory.java:156)
at org.apache.naming.factory.ResourceFactory.getObjectInstance(ResourceFactory.java:141)
at javax.naming.spi.NamingManager.getObjectInstance(NamingManager.java:321)
at org.apache.naming.NamingContext.lookup(NamingContext.java:842)
at org.apache.naming.NamingContext.lookup(NamingContext.java:153)
at org.apache.naming.NamingContext.lookup(NamingContext.java:830)
at org.apache.naming.NamingContext.lookup(NamingContext.java:167)
at org.apache.catalina.core.NamingContextListener.addResource(NamingContextListener.java:1103)
at org.apache.catalina.core.NamingContextListener.createNamingContext(NamingContextListener.java:682)
at org.apache.catalina.core.NamingContextListener.lifecycleEvent(NamingContextListener.java:271)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:117)
at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5416)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1575)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1565)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
** END NESTED EXCEPTION **
看配置文件，用客户端连接都是okay的，说明1、服务没起2、有防火墙3、用户名密码错误等都不是原因，再仔细看报错的是tomcat.dbcp的报错，而我的用的连接池是spring的，那为啥会报tomcat的dbcp错呢，回头再看tomcat中的server配置，发现在context.xml中配置了<Resource auth="Container" driverClassName="com.mysql.jdbc.Driver" initialSize="1" logAbandoned="true" maxActive="80" maxIdle="20" maxWait="10000" minIdle="1" name="jdbc/mysql5" password="bbb" removeAbandoned="true" removeAbandonedTimeout="180" testOnBorrow="true" type="javax.sql.DataSource" url="jdbc:mysql://1.1.1.1:3306/scan?characterEncoding=utf-8" username="aaa" validationQuery="select 1"/> 这么一行配置，原来tomcat启动的时候会优先读自己的配置文件，发现里面有数据库的配置，则创建tomcat.dbcp类型的连接池，而这个配置的网络不通，导致了timed out错误
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