解决数据库报错message from server: “Host ‘183.xxx.xxx.xx‘ is blocked because of many connection errors；

IDEA上跑Java项目，连接MySQL数据库时报错，错误如下:

Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'myDataSource' defined in ServletContext resource [/WEB-INF/config/db_mysql.xml]: Invocation of init method failed; nested exception is java.sql.SQLException: null,  message from server: "Host '183.xxx.xxx.xx' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'"
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1578)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:545)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
	at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
	at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:351)
	... 93 more
Caused by: java.sql.SQLException: null,  message from server: "Host '183.xxx.xxx.xx' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'"
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:965)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:898)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:887)
	at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1038)
	at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2199)
	at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2230)
	at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2025)
	at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:778)
	at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
	at sun.reflect.GeneratedConstructorAccessor31.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:425)
	at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:386)
	at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:330)
	at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:148)
	at com.alibaba.druid.filter.FilterAdapter.connection_connect(FilterAdapter.java:785)
	at com.alibaba.druid.filter.FilterEventAdapter.connection_connect(FilterEventAdapter.java:38)
	at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:142)
	at com.alibaba.druid.filter.stat.StatFilter.connection_connect(StatFilter.java:211)
	at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:142)
	at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1377)
	at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1431)
	at com.alibaba.druid.pool.DruidDataSource.init(DruidDataSource.java:632)
	at sun.reflect.GeneratedMethodAccessor46.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeCustomInitMethod(AbstractAutowireCapableBeanFactory.java:1706)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1645)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1574)
	... 100 more

一开始抓住了 nested exception is java.sql.SQLException: null, message from server: "Host '183.xxx.xxx.xx' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'"这点，即同一个ip在短时间内产生太多（超过mysql数据库max_connection_errors的最大值）中断的数据库连接而导致的阻塞，于是刷新记录报错host的文件，mysql>flush hosts;但是再次运行，还是报同样的错误！

参考：https://blog.youkuaiyun.com/ningjiebing/article/details/102408136

考虑到应用到 MySQL 服务器的网络延迟太大，数据库的connect_timeout = 10，网络延迟基本在 14 秒以上。参数max_connect_errors控制同一个 IP连接连续错误次数多过参数max_connect_errors的值时，这之后的连接mysql会阻止。

参考：https://blog.youkuaiyun.com/iris_xuting/article/details/102689000?spm=1001.2101.3001.6650.2&utm_medium=distribute.pc_relevant.none-task-blog-2%7Edefault%7ECTRLIST%7Edefault-2-102689000-blog-102408136.pc_relevant_blogantidownloadv1&depth_1-utm_source=distribute.pc_relevant.none-task-blog-2%7Edefault%7ECTRLIST%7Edefault-2-102689000-blog-102408136.pc_relevant_blogantidownloadv1

于是修改了数据库的connect_timeout为15秒。

mysql> use performance_schema;
mysql> set @@global.connect_timeout=15;

但是，结果同样是没有解决问题。这时，我开始考虑是数据库连接的问题。有资料显示，useSSL=true 时，数据库连接安全认证不通过，于是，我在数据库连接上加上 useSSL=false 。

https://blog.youkuaiyun.com/L_it123/article/details/106845391

url=jdbc:mysql://localhost:3306/mysql?useSSL=false&useUnicode=true&characterEncoding=UTF-8

终于，再次运行，可以连上数据库了！