web系统启动报错：mysql数据库连接many connection errors; unblock with 'mysqladmin flush-hosts' 解决方法

部署在客户生成环境的Web系统报错，启动报错如下

Caused by: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is org.apache.commons.dbcp.SQLNestedException: Cannot create PoolableConnectionFactory (null,  message from server: "Host 'host-172-16-18-13.openstacklocal' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'")

        at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:80)
        at org.mybatis.spring.transaction.SpringManagedTransaction.openConnection(SpringManagedTransaction.java:80)
        at org.mybatis.spring.transaction.SpringManagedTransaction.getConnection(SpringManagedTransaction.java:66)
        at org.apache.ibatis.executor.BaseExecutor.getConnection(BaseExecutor.java:279)
        at org.apache.ibatis.executor.SimpleExecutor.prepareStatement(SimpleExecutor.java:69)
        at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:56)
        at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:267)
        at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:141)
        at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:105)
        at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:81)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:606)
        at org.apache.ibatis.plugin.Invocation.proceed(Invocation.java:46)
        at cn.cecgw.goku.mybatis.dialect.interceptor.PaginationInterceptor.intercept(PaginationInterceptor.java:111)
        at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:57)
        at com.sun.proxy.$Proxy213.query(Unknown Source)
        at org.apache.ibatis.session.defaults.DefaultSqlSession.select(DefaultSqlSession.java:121)
        ... 86 common frames omitted

环境：linux，mysql5.5

错误：Host is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'

原因：

　　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；

解决方法：

1、提高允许的max_connection_errors数量（治标不治本）：

　　① 进入Mysql数据库查看max_connection_errors： show variables like '%max_connection_errors%';

　   ② 修改max_connection_errors的数量为1000：set global max_connect_errors = 1000;

　　③ 查看是否修改成功：show variables like '%max_connection_errors%';

2、使用mysqladmin flush-hosts 命令清理一下hosts文件（不知道mysqladmin在哪个目录下可以使用命令查找：whereis mysqladmin）；

　　① 在查找到的目录下使用命令修改：/usr/bin/mysqladmin flush-hosts -h192.168.1.1 -P3308-uroot -prootpwd;

　　备注：

　　　　其中端口号，用户名，密码都可以根据需要来添加和修改；

　　　　配置有master/slave主从数据库的要把主库和从库都修改一遍的（我就吃了这个亏明明很容易的几条命令结果折腾了大半天）；

　　　　第二步也可以在数据库中进行，命令如下：flush hosts;