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.(ConnectionImpl.java:778) at com.mysql.jdbc.JDBC4Connection. (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.csdn.net/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.csdn.net/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.csdn.net/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！
