如下所示：

logging:
 config: classpath:spring-logback.xml
 pattern:
 console: "%d - %msg%n"
 level: info

直接写 level: info 会报错：

org.springframework.boot.context.properties.bind.BindException: Failed to bind properties under 'logging.level' to java.util.Map<java.lang.String, java.lang.String>
...
Caused by: org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [java.lang.String] to type [java.util.Map<java.lang.String, java.lang.String>]
...

解决方法 ：加个root

logging:
 config: classpath:spring-logback.xml
 pattern:
 console: "%d - %msg%n"
 level: 
 root: info

运行成功