连接数据库：The last packet sent successfully to the server was 0 milliseconds ago问题解决

问题：

宿主机连接虚拟机上的mysql数据库。使用Navicat可以连接上，java代码连接报错

在springboot项目启动时报以下错误：

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:174) ~[mysql-connector-java-8.0.30.jar:8.0.30]
	at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:64) ~[mysql-connector-java-8.0.30.jar:8.0.30]
	at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:828) ~[mysql-connector-java-8.0.30.jar:8.0.30]
	at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:448) ~[mysql-connector-java-8.0.30.jar:8.0.30]
	at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:241) ~[mysql-connector-java-8.0.30.jar:8.0.30]
	at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:198) ~[mysql-connector-java-8.0.30.jar:8.0.30]
	at com.zaxxer.hikari.util.DriverDataSource.getConnection(DriverDataSource.java:138) ~[HikariCP-4.0.3.jar:na]
	at com.zaxxer.hikari.pool.PoolBase.newConnection(PoolBase.java:364) ~[HikariCP-4.0.3.jar:na]
	at com.zaxxer.hikari.pool.PoolBase.newPoolEntry(PoolBase.java:206) ~[HikariCP-4.0.3.jar:na]
	at com.zaxxer.hikari.pool.HikariPool.createPoolEntry(HikariPool.java:476) [HikariCP-4.0.3.jar:na]
	at com.zaxxer.hikari.pool.HikariPool.checkFailFast(HikariPool.java:561) [HikariCP-4.0.3.jar:na]
	at com.zaxxer.hikari.pool.HikariPool.<init>(HikariPool.java:115) [HikariCP-4.0.3.jar:na]
	at com.zaxxer.hikari.HikariDataSource.getConnection(HikariDataSource.java:112) [HikariCP-4.0.3.jar:na]
	at org.springframework.jdbc.datasource.DataSourceUtils.fetchConnection(DataSourceUtils.java:159) [spring-jdbc-5.3.23.jar:5.3.23]
	at org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection(DataSourceUtils.java:117) [spring-jdbc-5.3.23.jar:5.3.23]
	at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:80) [spring-jdbc-5.3.23.jar:5.3.23]
	at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:330) [spring-jdbc-5.3.23.jar:5.3.23]
	at org.springframework.boot.jdbc.EmbeddedDatabaseConnection.isEmbedded(EmbeddedDatabaseConnection.java:162) [spring-boot-2.7.4.jar:2.7.4]
	at org.springframework.boot.autoconfigure.orm.jpa.HibernateDefaultDdlAutoProvider.getDefaultDdlAuto(HibernateDefaultDdlAutoProvider.java:42) [spring-boot-autoconfigure-2.7.4.jar:2.7.4]
	at org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaConfiguration.lambda$getVendorProperties$1(HibernateJpaConfiguration.java:130) [spring-boot-autoconfigure-2.7.4.jar:2.7.4]
	at org.springframework.boot.autoconfigure.orm.jpa.HibernateSettings.getDdlAuto(HibernateSettings.java:41) ~[spring-boot-autoconfigure-2.7.4.jar:2.7.4]
	at org.springframework.boot.autoconfigure.orm.jpa.HibernateProperties.determineDdlAuto(HibernateProperties.java:143) ~[spring-boot-autoconfigure-2.7.4.jar:2.7.4]
	at org.springframework.boot.autoconfigure.orm.jpa.HibernateProperties.getAdditionalProperties(HibernateProperties.java:103) ~[spring-boot-autoconfigure-2.7.4.jar:2.7.4]
	at org.springframework.boot.autoconfigure.orm.jpa.HibernateProperties.determineHibernateProperties(HibernateProperties.java:95) ~[spring-boot-autoconfigure-2.7.4.jar:2.7.4]
	at org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaConfiguration.getVendorProperties(HibernateJpaConfiguration.java:132) [spring-boot-autoconfigure-2.7.4.jar:2.7.4]
	at org.springframework.boot.autoconfigure.orm.jpa.JpaBaseConfiguration.entityManagerFactory(JpaBaseConfiguration.java:132) ~[spring-boot-autoconfigure-2.7.4.jar:2.7.4]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_201]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_201]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_201]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_201]
	at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154) ~[spring-beans-5.3.23.jar:5.3.23]
	at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:653) ~[spring-beans-5.3.23.jar:5.3.23]
	at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:638) ~[spring-beans-5.3.23.jar:5.3.23]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1352) ~[spring-beans-5.3.23.jar:5.3.23]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1195) ~[spring-beans-5.3.23.jar:5.3.23]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:582) ~[spring-beans-5.3.23.jar:5.3.23]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542) ~[spring-beans-5.3.23.jar:5.3.23]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.23.jar:5.3.23]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.23.jar:5.3.23]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.23.jar:5.3.23]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.23.jar:5.3.23]
	at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1154) ~[spring-context-5.3.23.jar:5.3.23]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:908) ~[spring-context-5.3.23.jar:5.3.23]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:583) ~[spring-context-5.3.23.jar:5.3.23]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:147) ~[spring-boot-2.7.4.jar:2.7.4]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:734) ~[spring-boot-2.7.4.jar:2.7.4]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:408) ~[spring-boot-2.7.4.jar:2.7.4]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:308) ~[spring-boot-2.7.4.jar:2.7.4]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1306) ~[spring-boot-2.7.4.jar:2.7.4]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1295) ~[spring-boot-2.7.4.jar:2.7.4]
	at com.southwind.springboottest.SpringboottestApplication.main(SpringboottestApplication.java:10) ~[classes/:na]
	....

方式一

检查application.yml中的url路径是否正确

方式二

在application.yml的url中加入useSSL=false
如：url: jdbc:mysql://localhost:3306/library?useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai&useSSL=false

找了很久，本人的解决方式是第二种，加上useSSL=false就可以运行了。

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