Mysql连接时报错“Could not create connection to database server. Attempted reconnect 3 times.”

Mysql连接时报错“Could not create connection to database server. Attempted reconnect 3 times.”

今天搭建完项目，打算写一个简单的写入数据库的程序，没想到因为这个问题直接卡了好一会。

报错如下：

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.
	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:411)
	at com.mysql.jdbc.Util.getInstance(Util.java:386)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:920)
	at com.mysql.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:2404)
	at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2325)
	at com.mysql.jdbc.ConnectionImpl.(ConnectionImpl.java:834)
	at com.mysql.jdbc.JDBC4Connection.(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:411)
	at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:416)
	at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:347)
	at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:175)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:220)
	at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1138)
	at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1125)
	at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)
	at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1870)
	at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)
Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

我的 C3P0_JDBCURL配置，如下：

C3P0_JDBCURL= "jdbc:mysql://ip:3306/database?useUnicode=true&characterEncoding=utf-8&autoReconnect=true&failOverReadOnly=false&useSSL=true";

报错原因：

查阅资料发现这都是因为安装mysql的时候时区设置的不正确 ，mysql默认的是美国的时区，而我们要比他们迟8小时，采用+8:00格式。使用的数据库是MySQL，在你没有指定MySQL驱动版本的情况下它自动依赖的驱动是8.0.12很高的版本，这是由于数据库和系统时区差异所造成的，

解决办法：

1. 在jdbc连接的url后面加上serverTimezone=GMT即可解决问题，如果需要使用gmt+8时区，需要写成GMT%2B8，否则会被解析为空。

2. 再一个解决办法就是使用低版本的MySQL jdbc驱动，5.1.28不会存在时区的问题。

具体操作：

在连接字符串后面加上?serverTimezone=UTC
其中UTC是统一标准世界时间。
完整的连接字符串示例：

jdbc:mysql://ip:3306/database?serverTimezone=UTC

或者还有另一种选择：jdbc:mysql://127.0.0.1:3306/database?useUnicode=true&characterEncoding=UTF-8，这个是解决中文乱码输入问题，当然也可以和上面的一起结合：

jdbc:mysql://ip:3306/database?useUnicode=true&characterEncoding=UTF-8&serverTimezone=UTC?serverTimezone=UTC

另一种情况改成：

jdbc:mysql://ip:3306/database?serverTimezone=GMT 

jdbc是mysql-connector-java-8.0.11.jar，设置过时区 set time_zone = ‘+8:00’

总结：

出现这个问题先看自己系统设置的时区是UTC还是GMT,再找对应的解决办法。