今天在弄数据库迁移及部署到客户服务器时，发现启动成功了，但是数据请求超时，赶紧打开日志看一下，报了这样的错：
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
at com.mysql.cj.jdbc.exceptions.SQLError.createCommunicationsException(SQLError.java:174)
at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:64)
at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:835)
at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:455)
at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:240)
at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:207)
at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:156)
at com.alibaba.druid.filter.stat.StatFilter.connection_connect(StatFilter.java:218)
at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:150)
at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1560)
at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1623)
at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:2468)
Caused by: com.mysql.cj.exceptions.CJCommunicationsException: Communications link failure
java.sql.SQLException: null, message from server: "Host '10.21.5.91' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'"
发现是数据库连接失败导致的，上下配置
分析了下由于项目中使用了阿里的数据库连接池Driud，配置了连接失败会重新连接，没过一会超过mysql配置最大失败连接数了，这边考虑是客户数据库的问题，马上作出了相关修改
1.修改了最大连接数以及最大失败数
2.数据库开启远程访问
3.有可能是数据库回收了连接，而系统的缓冲池不知道，继续使用被回收的连接所致的。所以将回收时间延长
重启之后，发现仍然连不上，网上看了不少帖子也试了，都不行
这边决定再看一下报错，发现是嵌套的异常
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(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:61)
at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:105)
at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:151)
at com.mysql.cj.exceptions.ExceptionFactory.createCommunicationsException(ExceptionFactory.java:167)
at com.mysql.cj.protocol.a.NativeProtocol.negotiateSSLConnection(NativeProtocol.java:351)
at com.mysql.cj.protocol.a.NativeAuthenticationProvider.negotiateSSLConnection(NativeAuthenticationProvider.java:777)
at com.mysql.cj.protocol.a.NativeAuthenticationProvider.proceedHandshakeWithPluggableAuthentication(NativeAuthenticationProvider.java:486)
at com.mysql.cj.protocol.a.NativeAuthenticationProvider.connect(NativeAuthenticationProvider.java:202)
at com.mysql.cj.protocol.a.NativeProtocol.connect(NativeProtocol.java:1442)
at com.mysql.cj.NativeSession.connect(NativeSession.java:165)
at com.mysql.cj.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:955)
at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:825)
... 9 common frames omitted
Caused by: javax.net.ssl.SSLHandshakeException: No appropriate protocol (protocol is disabled or cipher suites are inappropriate)
at sun.security.ssl.Handshaker.activate(Handshaker.java:554)
at sun.security.ssl.SSLSocketImpl.kickstartHandshake(SSLSocketImpl.java:1495)
at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1367)
at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1416)
at
发现在调用ssl时报错了
javax.net.ssl.SSLHandshakeException: No appropriate protocol (protocol is disabled or cipher suites are inappropriate)，这句话翻译过来就是没有合适的协议(协议被禁用或密码套件不合适)，想了一下连接数据库方面用到加密的地方，赶紧看了下jdbc参数，用的是useSSL=true ，又看了下去客户的mysql版本
哎草率了！之前开发测试用的都是8的版本，MySQL在高版本需要指明需要进行SSL连接，(保障Internet数据传输安全利用数据加密)需要在url后面添加useSSL=true或者false，
useSSL=true 需要连接
useSSL=false 不需要连接
改成false，在部署启动项目，解决了，
具体这地方为什么要这样设置，可能要去了解不少东西，搜了下说是需要为服务器校验提供受信任的存储库，也就是ssl客户端证书密匙，不然连接失败，有大佬了解的清楚的，赐教一下，不胜感激！