Caused by: java.net.ConnectException: Connection refused: connect或者Caused by: com.mysql.jdbc.excepti

当出现如下三种错误：

Caused by: java.net.ConnectException: Connection refused: connect

[Druid-ConnectionPool-Create-1044694757] com.alibaba.druid.support.logging.JakartaCommonsLoggingImpl.error create connection SQLException, url: jdbc:mysql:///atguigu?characterEncoding=utf-8, errorCode 0, state 08S01
 com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

查询了网上很多的资料，大概说是有下面几种原因：
1.端口号被占用，修改8080的端口号进程
2.当数据库重启或数据库空闲连接超过设置的最大timemout时间，数据库会强行断开已有的链接，最大timeout时间可以通过命令

还有一些其他的原因。

但是
以上别人出错的环境是正儿八经的工业生产环境

我TM就按照视频教程来一步一步的操作，根本不会涉及到这些高深的错误。（想想看，连Tomcat服务器都是安装在本地win10上的）

昨晚遇到这个问题，查来查去，浪费了好几个小时，而且还把之前自己手写的项目代码全部删除了。然后使用的视频提供的阶段源码

昨晚是能使用了

今早起来又出现上述错误。

气得我快疯了。

后来注意到上面别人遇到的问题，说是数据库的某些问题。

然后本来想着按照上述第二条的解决方案操作一下。结果在win10 命令提示符之下 ，输入 mysql -uroot -p 再输入密码，发现进不去。想到这是因为服务没开。然后通过【cortana】->【服务】->【MySQL服务】，居然是关着的！（启动方式为手动）

启动这个服务，并且把启动方式也设置为自动。发现一直在启动连接状态的Tomcat服务器突然在浏览器蹦出来一个网页！！！【成功了！】

总结
所以以后再碰到这样的错误时，首先看看MySQL服务开了没有。。。

02-Sep-2020 10:19:14.644 严重 [Druid-ConnectionPool-Create-1044694757] com.alibaba.druid.support.logging.JakartaCommonsLoggingImpl.error create connection SQLException, url: jdbc:mysql:///atguigu?characterEncoding=utf-8, errorCode 0, state 08S01
 com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Last packet sent to the server was 0 ms ago.
	at sun.reflect.GeneratedConstructorAccessor9.newInstance(Unknown Source)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
	at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
	at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074)
	at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2120)
	at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:723)
	at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:46)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
	at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
	at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:302)
	at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:282)
	at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1558)
	at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1623)
	at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:2468)
Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Last packet sent to the server was 0 ms ago.
	at sun.reflect.GeneratedConstructorAccessor9.newInstance(Unknown Source)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
	at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
	at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074)
	at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:335)
	at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2043)
	... 12 more
Caused by: 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: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:606)
	at java.net.Socket.connect(Socket.java:555)
	at java.net.Socket.<init>(Socket.java:451)
	at java.net.Socket.<init>(Socket.java:261)
	at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:253)
	at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:284)
	... 13 more