修改前：

spring前面空格了
报错输出：Failed to configure a DataSource: ‘url’ attribute is not specified and no embedded datasource could be configured.

Reason: Failed to determine a suitable driver class

Action:

Consider the following:
If you want an embedded database (H2, HSQL or Derby), please put it on the classpath.
If you have database settings to be loaded from a particular profile you may need to activate it (no profiles are currently active).

修改后：

总结
YAML文件对缩进非常敏感，必须使用空格（通常为2个空格）来表示层次结构，不能使用Tab键。