MySql连接异常问题

在MySql安装好之后，命令行登录和使用一切正常，但是使用Web服务连接，报以下错误，无法使用

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:425)
	at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:989)
	at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:341)
	at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2196)
	at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2229)
	at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2024)
	at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:779)
	at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
	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:425)
	at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:389)
	at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:330)
	at java.sql.DriverManager.getConnection(Unknown Source)
	at java.sql.DriverManager.getConnection(Unknown Source)
	at com.ad.MysqlDemo.main(MysqlDemo.java:32)
Caused by: java.net.ConnectException: Connection refused: connect
	at java.net.DualStackPlainSocketImpl.connect0(Native Method)
	at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
	at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
	at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
	at java.net.AbstractPlainSocketImpl.connect(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:211)
	at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:300)
	... 15 more
Exception in thread "main" java.lang.NullPointerException
	at com.ad.MysqlDemo.main(MysqlDemo.java:57)

经过多轮百度，结果都不是我想要的，最后通过错误本身

The last packet sent successfully to the server was 0 milliseconds ago

分析可能由于系统时间导致出现连接问题。

在这之前，由于使用rpm安装包安装的MySql出现问题，无法启动，在处理过程中，错误地将服务器EST时间改成了和UTC时间一致，导致服务器时间比实际时间快了很多，导致出现该问题。