具体报错如下

严重: create connection SQLException, url: jdbc:mysql://localhost:3306/db2?&useSSL=false&serverTimezone=UTC, errorCode 1045, state 28000
java.sql.SQLException: Access denied for user ‘Administrator‘@‘localhost‘ (using password: YES)
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129)
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
	at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122)
	at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:835)
	at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:455)
	at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:240)
	at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:199)
	at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1644)
	at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1710)
	at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:2753)

明明密码对的，被拒绝了，找了好久原因，后来发现将db.properties配置文件里的username改为jdbc.username就好了，可能是因为username被系统变量占用了。
当spring容器在进行启动的时候，会读取当前系统某些环境变量的配置，当前系统的用户名使用username来表示的，所以做好的方式是添加前缀，使用jdbc.username.

jdbc.username=root
jdbc.password=root
jdbc.url=jdbc:mysql://localhost:3306/db2?&useSSL=false&serverTimezone=UTC
jdbc.driverClassName=com.mysql.cj.jdbc.Driver

java.sql.SQLException: Access denied for user 'Administrator'@'localhost' (using password: YES)