数据库连接错误：Communications link failure due to underlying exception

过了年回来，调整好状态后，继续进行springcloud的学习！

今天的学习中又碰到了一个之前没碰到的问题，数据库连接错误：Communications link failure due to underlying exception，具体错误信息如下所示：

[org.jboss.resource.connectionmanager.JBossManagedConnectionPool] Throwable while attempting to get a new connection: null
org.jboss.resource.JBossResourceException: Could not create connection; - nested throwable: (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:1934)
    at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2380)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2909)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:798)
    at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:3700)
    at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1203)
    at com.mysql.jdbc.Connection.createNewIO(Connection.java:2572)
    at com.mysql.jdbc.Connection.<init>(Connection.java:1485)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:266)
    at org.jboss.resource.adapter.jdbc.local.LocalManagedConnectionFactory.createManagedConnection(LocalManagedConnectionFactory.java:172)
    at org.jboss.resource.connectionmanager.InternalManagedConnectionPool.createConnectionEventListener(InternalManagedConnectionPool.java:619)
    at org.jboss.resource.connectionmanager.InternalManagedConnectionPool.getConnection(InternalManagedConnectionPool.java:264)
    at org.jboss.resource.connectionmanager.JBossManagedConnectionPool$BasePool.getConnection(JBossManagedConnectionPool.java:575)
    at org.jboss.resource.connectionmanager.BaseConnectionManager2.getManagedConnection(BaseConnectionManager2.java:347)
    at org.jboss.resource.connectionmanager.TxConnectionManager.getManagedConnection(TxConnectionManager.java:330)
    at org.jboss.resource.connectionmanager.BaseConnectionManager2.allocateConnection(BaseConnectionManager2.java:402)
    at org.jboss.resource.connectionmanager.BaseConnectionManager2$ConnectionManagerProxy.allocateConnection(BaseConnectionManager2.java:849)
    at org.jboss.resource.adapter.jdbc.WrapperDataSource.getConnection(WrapperDataSource.java:89)
    at sun.reflect.GeneratedMethodAccessor109.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:112)
    at org.jboss.ejb3.interceptor.InvocationContextImpl.proceed(InvocationContextImpl.java:166)
    at org.jboss.ejb3.interceptor.EJB3InterceptorsInterceptor.invoke(EJB3InterceptorsInterceptor.java:63)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
    at org.jboss.ejb3.entity.TransactionScopedEntityManagerInterceptor.invoke(TransactionScopedEntityManagerInterceptor.java:54)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
    at org.jboss.ejb3.AllowedOperationsInterceptor.invoke(AllowedOperationsInterceptor.java:47)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
    at org.jboss.ejb3.tx.BMTInterceptor.handleStateless(BMTInterceptor.java:71)
    at org.jboss.ejb3.tx.BMTInterceptor.invoke(BMTInterceptor.java:131)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
    at org.jboss.aspects.tx.TxPropagationInterceptor.invoke(TxPropagationInterceptor.java:95)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
    at org.jboss.ejb3.stateless.StatelessInstanceInterceptor.invoke(StatelessInstanceInterceptor.java:62)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
    at org.jboss.aspects.security.AuthenticationInterceptor.invoke(AuthenticationInterceptor.java:77)
    at org.jboss.ejb3.security.Ejb3AuthenticationInterceptor.invoke(Ejb3AuthenticationInterceptor.java:110)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
    at org.jboss.ejb3.ENCPropagationInterceptor.invoke(ENCPropagationInterceptor.java:46)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
    at org.jboss.ejb3.asynchronous.AsynchronousInterceptor.invoke(AsynchronousInterceptor.java:106)
    at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:101)
    at org.jboss.ejb3.stateless.StatelessContainer.dynamicInvoke(StatelessContainer.java:304)
    at org.jboss.aop.Dispatcher.invoke(Dispatcher.java:106)
    at org.jboss.aspects.remoting.AOPRemotingInvocationHandler.invoke(AOPRemotingInvocationHandler.java:82)
    at org.jboss.remoting.ServerInvoker.invoke(ServerInvoker.java:809)
    at org.jboss.remoting.transport.socket.ServerThread.processInvocation(ServerThread.java:608)
    at org.jboss.remoting.transport.socket.ServerThread.dorun(ServerThread.java:420)
    at org.jboss.remoting.transport.socket.ServerThread.run(ServerThread.java:173)

** END NESTED EXCEPTION **

Last packet sent to the server was 22 ms ago.)

看了半天报错信息，也没看出什么名堂来，于是求助百度，百度上给的答案大多都是提高mysql端的timeout值，或者降低连接池这边的timeout值，我也尝试着去改了，还有一些其他的解决方案，但在我这儿都行不通，我就纳闷了，咋回事，然后一想会不会是我的mysql服务停了？然后赶紧看看，果然，本地mysql服务没有启，那肯定是连接不上咯！

启动一下mysql服务，然后再次访问，一切正常！

顺便说一下启动mysql服务的方法吧：

方法1：

windows+R打开cmd命令行界面，输入 net start mysql，即可启动mysql服务，如下图