springboot連接mysql報錯：com.mysql.jdbc.exceptions.jdbc4.CommunicationsException

nested exception is org.apache.ibatis.exceptions.PersistenceException: ### Error querying database. Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up. ### The error may exist in file [D:\JavaProject\dataservice\target\classes\mybatis\mapper\ClassificationMapper.xml] ### The error may involve com.tjhnode.dataservice.mapper.ClassificationMapper.findAll ### The error occurred while executing a query ### Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.

出現此錯誤以為是連接超時，百度答案大多是修改mysql的my.ini配置文件，設置wait_timeout時長，但是並沒有解決問題。

經過分析，首先我猜想是application.yml中無法使用localhost訪問，於是修改修改mysql允許ip地址訪問

1.進入mysql命令行，輸入select host,user from mysql.user; 

  發現所有host字段均為localhost；

2.設置允許被任意IP地址訪問，執行 update mysql.user set host = '%' where user = 'root';

   然后執行  flush privileges;  刷新MySQL的系統權限相關表，客戶端工具使用ip測試連接成功

  重新運行項目，訪問依舊報錯，經過百度猜想大概是mysql驅動配置問題

3.修改application.yml中數據庫連接配置，將localhost換成ip，另外，url 需要添加時區設置：&serverTimezone=UTC，

  我使用的mysql版本是8.0.17，而mysql6.0以上對應的驅動要使用 com.mysql.cj.jdbc.Driver

spring:
  datasource:
    #   數據源基本配置
    username: root
    password: 123456
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://192.168.135.1:3306/test?useUnicode=true&characterEncoding=utf8&useSSL=false&serverTimezone=UTC
    type: com.alibaba.druid.pool.DruidDataSource

pom文件依賴

<dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.17</version>
</dependency>

重新運行，成功訪問 http://localhost:8080/findAll，