MySQL数据库链接问题：The last packet sent successfully to the server was 0 milliseconds ago.

JDBC链接mysql8.0
新装了MySQL 8，并下载mysql-connector-java-8.0.11.jar，但在链接时出现了下面问题，折腾半天发现是URL的问题，终于解决。
出现的问题错误：

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:172)
	at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:64)
	at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:862)
	at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:444)
	at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:230)
	at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:226)
	at java.sql.DriverManager.getConnection(DriverManager.java:664)
	at java.sql.DriverManager.getConnection(DriverManager.java:247)
	at com.jie.Dao.DCDao.getCon(DCDao.java:20)
	at com.jie.Dao.DCDao.main(DCDao.java:37)
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:59)
	at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:103)
	at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:149)
	at com.mysql.cj.exceptions.ExceptionFactory.createCommunicationsException(ExceptionFactory.java:165)
	at com.mysql.cj.protocol.a.NativeProtocol.negotiateSSLConnection(NativeProtocol.java:355)
	at com.mysql.cj.protocol.a.NativeAuthenticationProvider.negotiateSSLConnection(NativeAuthenticationProvider.java:789)
	at com.mysql.cj.protocol.a.NativeAuthenticationProvider.proceedHandshakeWithPluggableAuthentication(NativeAuthenticationProvider.java:499)
	at com.mysql.cj.protocol.a.NativeAuthenticationProvider.connect(NativeAuthenticationProvider.java:217)
	at com.mysql.cj.protocol.a.NativeProtocol.connect(NativeProtocol.java:1411)
	at com.mysql.cj.NativeSession.connect(NativeSession.java:165)
	at com.mysql.cj.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:982)
	at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:852)
	... 7 more
null

解决方法：
修改URL为：

String URL="jdbc:mysql://localhost:3306/test?useSSL=false&serverTimezone=UTC&allowPublicKeyRetrieval=true";`