报错信息：

java.sql.SQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.

Caused by: com.mysql.cj.exceptions.CJException: Unknown database '${hm.db.database}'

can not init dataSource

Error creating bean with name 'dataSource' defined in class path resource [org/springframework/boot/autoconfigure/jdbc/DataSourceConfiguration$Hikari.class]: Initialization of bean failed; nested exception is java.lang.IllegalStateException: can not init dataSource

解决：

不用怀疑，就是数据库连接配置有问题，使用dbms检查一下数据库连接是否成功，不成功就检查jdbc的连接信息是不是写错了，数据库ip呀，用户名密码呀，数据库名称呀；成功就说明项目里的properties或者yaml配置文件写错了，某个字母输错了比如database写成datebase之类的