”The last packet sent successfully to the server was 0 milliseconds ago“的解决过程

”The last packet sent successfully to the server was 0 milliseconds ago“的解决过程 项目场景：

动态注册jdbc驱动程序,建立数据库连接读取数据库中的数据。mysql版本是5.7，mysql驱动包为mysql-connector-java8.0.16，ubuntu16.04。

问题描述：

报错信息如下：

com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure

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.(ConnectionImpl.java:455)
 at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:240)
 at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:199)
 at java.sql.DriverManager.getConnection(DriverManager.java:664)
 at java.sql.DriverManager.getConnection(DriverManager.java:247)
 at com.Demo1.main(Demo1.java:22)
Caused by: com.mysql.cj.exceptions.CJCommunicationsException: Communications link failure

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:361)
 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:1452)
 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)
 ... 6 more
Caused by: javax.net.ssl.SSLHandshakeException: No appropriate protocol (protocol is disabled or cipher suites are inappropriate)
 at sun.security.ssl.HandshakeContext.(HandshakeContext.java:171)
 at sun.security.ssl.ClientHandshakeContext.(ClientHandshakeContext.java:98)
 at sun.security.ssl.TransportContext.kickstart(TransportContext.java:220)
 at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:428)
 at com.mysql.cj.protocol.ExportControlled.performTlsHandshake(ExportControlled.java:316)
 at com.mysql.cj.protocol.StandardSocketFactory.performTlsHandshake(StandardSocketFactory.java:188)
 at com.mysql.cj.protocol.a.NativeSocketConnection.performTlsHandshake(NativeSocketConnection.java:99)
 at com.mysql.cj.protocol.a.NativeProtocol.negotiateSSLConnection(NativeProtocol.java:352)
 ... 13 more

---

原因分析：

（1）可能是mysql服务没有开启
（2）连接数据库的url不正确

解决方案：

(1)开启mysql服务

service mysql start

（2）检查数据库连接是否配置正确。在
数据库名称后添加 ?useSSL=false&useUnicode=true&characterEncoding=utf-8&useLegacyDatetimeCode=false&serverTimezone=UTC
修改前：

String url="jdbc:mysql://localhost:3306/runoob?serverTimezone=UTC";

修改后：

String url="jdbc:mysql://localhost:3306/runoob?useSSL=false&useUnicode=true&characterEncoding=utf-8&useLegacyDatetimeCode=false&serverTimezone=UTC";

其中的参数含义如下：

useSSL：表示是否需要建立 SSL 连接的。这里将它显示关闭。
allowPublicKeyRetrieval：表示是否允许客户端从服务器获取公钥。
serverTimezone：设置CST时区。

至于为什么要添加这些参数，尚不清楚，因为看到别人在windows下使用mysql8.0也没有出现过这种错误，难道是因为我用的是mysql5.7？经过查阅，发现 MySQL驱动5.1有userLegacyDatetimeCode和userTimezone两个参数，默认为userLegacyDatetimeCod=true&userTimezone=false。而MySQL驱动8.0中没有userLegacyDatetimeCode和userTimezone两个参数，所以一定要配置serverTimezone为MySQL运行的时区. 连接建立时会将这个时区存储到连接中。
另外，还需要注意驱动包、mysql、java三者之间得对应版本，否则也是会出现各种错误的。

• mysql-connector-java与Mysql对应版本：
  官方更推荐MySQL5.6以上使用connector/j 8.0
• mysql-connector-java与Mysql对应版本：
  参考资料：
  1、Java与MySQL时间戳传递/存储/协调问题–userLegacyDatetimeCode–userTimezone–serverTimezone
  2、https://blog.csdn.net/shiqidide/article/details/7642531
  3、mysql、驱动包、java对应版本