【已解决】com.mysql.jdbc.exceptions.jdbc4.CommunicationsExcepti：Communications link failure ----mysql连接报错

使用idea做项目时，连接mysql时报错；

报错如下：

The last packet successfully received from the server was 1,548 milliseconds ago.  The last packet sent successfully to the server was 1,540 milliseconds ago.
### The error may exist in com/liu/dao/StudentMapper.xml
### The error may involve com.liu.dao.StudentMapper.getStudentById
### The error occurred while executing a query
### Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was 1,548 milliseconds ago.  The last packet sent successfully to the server was 1,540 milliseconds ago.

	at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:149)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:140)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:76)
	at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:87)
	at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:93)
	at com.sun.proxy.$Proxy4.getStudentById(Unknown Source)
	at MyTest.getStudent(MyTest.java:101)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)
Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

最终查找原因解决办法如下；

第一种：

我之前使用的mysql版本是 5.7  驱动使用的是 com.mysql.jdbc.Driver

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=UTF-8

原因：useSSL=true时 数据库连接 安全认证不通过 

解决办法：将useSSL true改为false  （可以使用）

第二种办法：

更换JDBC驱动：使用：com.mysql.cj.jdbc.Driver （需注意：需要指定时区serverTimezone:）

driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=UTF-8&serverTimezone=UTC

最终使用了第二种办法 并且更换了连接驱动的版本 之前为 5.1的

        mysql
        mysql-connector-java
        8.0.20