In Spring Boot the default logging solution is logback

We want it to split the output between stderr and stdout depending on the log level.

This can be done with the following logback.xml found at https://gist.github.com/jeroenr/e5e54af6bc1868216a9da58f1e2f5984 :

<configuration>
    <appender name="STDERR" class="ch.qos.logback.core.ConsoleAppender">
        <target>System.err</target>
        <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
            <level>WARN</level>
        </filter>
        <encoder>
            <pattern>%-5level %logger : %msg%n</pattern>
        </encoder>
    </appender>
    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <target>System.out</target>
        <filter class="ch.qos.logback.classic.filter.LevelFilter">
            <level>DEBUG</level>
            <onMatch>ACCEPT</onMatch>
        </filter>
        <filter class="ch.qos.logback.classic.filter.LevelFilter">
            <level>INFO</level>
            <onMatch>ACCEPT</onMatch>
        </filter>
        <filter class="ch.qos.logback.classic.filter.LevelFilter">
            <level>TRACE</level>
            <onMatch>ACCEPT</onMatch>
        </filter>
        <filter class="ch.qos.logback.classic.filter.LevelFilter">
            <level>WARN</level>
            <onMatch>DENY</onMatch>
        </filter>
        <filter class="ch.qos.logback.classic.filter.LevelFilter">
            <level>ERROR</level>
            <onMatch>DENY</onMatch>
        </filter>
        <encoder>
            <pattern>%-5level %logger : %msg%n</pattern>
        </encoder>
    </appender>
    <root level="INFO">
        <appender-ref ref="STDOUT" />
        <appender-ref ref="STDERR" />
    </root>
</configuration>