请给出具体的报错提示

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

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)

at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)

at java.lang.reflect.Constructor.newInstance(Unknown Source)

at com.mysql.jdbc.Util.handleNewInstance(Util.java:400)

at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1038)

at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:339)

at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2247)

at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2280)

at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2079)

at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:794)

at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:44)

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)

at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)

at java.lang.reflect.Constructor.newInstance(Unknown Source)

at com.mysql.jdbc.Util.handleNewInstance(Util.java:400)

at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:399)

at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:325)

at java.sql.DriverManager.getConnection(Unknown Source)

at java.sql.DriverManager.getConnection(Unknown Source)

at com.xnj.dao.Dao.<clinit>(Dao.java:47)

at com.xnj.login.LoginDialog$2.actionPerformed(LoginDialog.java:86)

at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)

at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)

at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)

at javax.swing.DefaultButtonModel.setPressed(Unknown Source)

at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)

at java.awt.Component.processMouseEvent(Unknown Source)

at javax.swing.JComponent.processMouseEvent(Unknown Source)

at java.awt.Component.processEvent(Unknown Source)

at java.awt.Container.processEvent(Unknown Source)

at java.awt.Component.dispatchEventImpl(Unknown Source)

at java.awt.Container.dispatchEventImpl(Unknown Source)

at java.awt.Component.dispatchEvent(Unknown Source)

at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)

at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)

at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)

at java.awt.Container.dispatchEventImpl(Unknown Source)

at java.awt.Window.dispatchEventImpl(Unknown Source)

at java.awt.Component.dispatchEvent(Unknown Source)

at java.awt.EventQueue.dispatchEvent(Unknown Source)

at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)

at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)

at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)

at java.awt.EventDispatchThread.pumpEvents(Unknown Source)

at java.awt.EventDispatchThread.pumpEvents(Unknown Source)

at java.awt.EventDispatchThread.run(Unknown Source)

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

at java.net.PlainSocketImpl.socketConnect(Native Method)

at java.net.PlainSocketImpl.doConnect(Unknown Source)

at java.net.PlainSocketImpl.connectToAddress(Unknown Source)

at java.net.PlainSocketImpl.connect(Unknown Source)

at java.net.SocksSocketImpl.connect(Unknown Source)

at java.net.Socket.connect(Unknown Source)

at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:214)

at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:298)

... 41 more

https://blog.csdn.net/zouxucong/article/details/53924414

参考一下这个贴，改一下mysql的响应时间