解決：com.alibaba.druid.pool.DruidDataSource : {dataSource-1} closed

這是因為我的數據庫連接的driver參數寫錯了。
下面是修正的：

spring.datasource.druid.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.druid.url=jdbc:mysql://localhost:3306/springbootdata?useUnicode=true&zeroDateTimeBehavior=convertToNull&autoReconnect=true&characterEncoding=utf-8
spring.datasource.username=root
spring.datasource.password=admin