The last packet successfully received from the server was 20 milliseconds ago. 问题排查

今天启动ideal 打开本地项目报错，如下：
The last packet successfully received from the server was 20 milliseconds ago.  The last packet sent successfully to the server was 20 milliseconds ago.
    at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessProperties(CommonAnnotationBeanPostProcessor.java:324) ~[spring-context-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1378) ~[spring-beans-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:575) ~[spring-beans-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:498) ~[spring-beans-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320) ~[spring-beans-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory$$Lambda$106/10041107.getObject(Unknown Source) ~[na:na]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318) ~[spring-beans-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:846) ~[spring-beans-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:863) ~[spring-context-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:546) ~[spring-context-5.1.3.RELEASE.jar:5.1.3.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:142) ~[spring-boot-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:775) [spring-boot-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) [spring-boot-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:316) [spring-boot-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260) [spring-boot-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248) [spring-boot-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at com.yawn.ActivitiDemo6SpringbootApplication.main(ActivitiDemo6SpringbootApplication.java:17) [classes/:na]
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userService': Injection of resource dependencies failed; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'identityServiceBean' defined in class path resource [org/activiti/spring/boot/DataSourceProcessEngineAutoConfiguration$DataSourceProcessEngineConfiguration.class]: Unsatisfied dependency expressed through method 'identityServiceBean' parameter 0; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'processEngine': FactoryBean threw exception on object creation; nested exception is org.activiti.engine.ActivitiException: couldn't check if tables are already present using metadata: Communications link failure
 

这个报错是链接mysql数据库报错，翻看网上好多文章，有说是修改my.ini文件，延长数据库超时时间（结果证明没用）；有说连接错误的数据库，数据库不存在（结果也不是）。

真正的原因分析：

先看看mysql数据库连接

这里有个useSSL=true的参数，MySQL在高版本需要指明是否进行SSL连接。

SSL协议提供服务主要：
1）认证用户服务器，确保数据发送到正确的服务器； 　　 .
2）加密数据，防止数据传输途中被窃取使用；
3）维护数据完整性，验证数据在传输过程中是否丢失；
当前支持SSL协议两层：
SSL记录协议（SSL Record Protocol）：建立靠传输协议（TCP）高层协议提供数据封装、压缩、加密等基本功能支持
SSL握手协议（SSL Handshake Protocol）：建立SSL记录协议用于实际数据传输始前通讯双进行身份认证、协商加密
算法、 交换加密密钥等。

不建议在没有服务器身份验证的情况下建立SSL连接。根据MySQL 5.5.45+、5.6.26+和5.7.6+的要求，如果不设置显式选项，则必须建立默认的SSL连接。需要通过设置useSSL=false来显式禁用SSL，或者设置useSSL=true并为服务器证书验证提供信任存储。

所以建议设置useSSL为false.

解决方案，将useSSL=false，问题解决。