Log4j set a different logging level for each appender

Question

I'm using Log4j 2 to log the events of my application. However I'm stuck at the following problem.

Currently all logging messages are being written to two different appenders. One has RollingFile type, while the other has Console type.

What I want is for the RollingFile appender to log messages with an INFO level or higher (ERROR, FATAL), and for the Console appender to log messages with an ERROR level or higher (FATAL).

Inside my log4j2.xml file I seem to be only able to declare the logging level for an entire logger (including all of its appenders). Here is my log4j2.xml file:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration monitorInterval="30">
    <Appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <PatternLayout>
                <Pattern>%d %level %msg%n</Pattern>
            </PatternLayout>
        </Console>
        
        <RollingFile name="Log" fileName="log/Log.log" filePattern="log/Log-%d{yyyy-MM-dd}-%i.log" append="false">
            <PatternLayout>
                <Pattern>%d %level %msg%n</Pattern>
            </PatternLayout>
            <Policies>
                <SizeBasedTriggeringPolicy size="1 MB" />
            </Policies>
            <DefaultRolloverStrategy max="10"/>
        </RollingFile>
    </Appenders>

    <Loggers>
        <Root level="info">
            <AppenderRef ref="Console" />
            <AppenderRef ref="Log" />
        </Root>
    </Loggers>
</Configuration>

Is there an easy way of doing so? I searched log4j documentation but couldn't find what I was looking for (Maybe I missed it?). If it's possible I would really prefer for the solution to be applicable on any appenders' types; not specific for RollingFile and Console.

EDIT:

我看到很多问题，要求仅将特定级别的消息写入文件，而将不同级别的消息写入不同的文件。就我而言，我需要将具有一定级别的HIGHER的消息写入不同的文件。例如，在我提供级别为 ERROR 或 FATAL 的消息的情况下，将写入 RollingFile 和 Console，而级别为 INFO 的消息将仅写入 RollingFile。

Answer 1

要限制 log4j2 中特定附加程序的日志记录级别，您应该使用附加程序的ThresholdFilter元素。

在您的情况下，log4j2.xml 文件将如下所示：

<?xml version="1.0" encoding="UTF-8"?>
<Configuration monitorInterval="30">
    <Appenders>
        <Console name="Console" target="SYSTEM_OUT">
            <ThresholdFilter level="ERROR" onMatch="ACCEPT" onMismatch="DENY"/>
            <PatternLayout>
                <Pattern>%d %level %msg%n</Pattern>
            </PatternLayout>
        </Console>
    
        <RollingFile name="Log" fileName="log/Log.log" filePattern="log/Log-%d{yyyy-MM-dd}-%i.log" append="false">
            <ThresholdFilter level="INFO" onMatch="ACCEPT" onMismatch="DENY"/>
            <PatternLayout>
                <Pattern>%d %level %msg%n</Pattern>
            </PatternLayout>
            <Policies>
                <SizeBasedTriggeringPolicy size="1 MB" />
            </Policies>
            <DefaultRolloverStrategy max="10"/>
        </RollingFile>
    </Appenders>

    <Loggers>
        <Root level="info">
            <AppenderRef ref="Console" />
            <AppenderRef ref="Log" />
        </Root>
    </Loggers>
</Configuration>

这是一个简单的测试：

public class Log4jTest {
    private static final Logger logger = LogManager.getLogger(Log4jTest.class);

    public static void main(String[] args) {
        logger.debug("Debug");
        logger.info("Info");
        logger.warn("Warning");
        logger.error("Error");
        logger.fatal("Fatal");
    }
}

控制台输出：

2020-02-25 12:33:50,587 ERROR Error
2020-02-25 12:33:50,589 FATAL Fatal

Log.log内容：

2020-02-25 12:33:50,585 INFO Info
2020-02-25 12:33:50,587 WARN Warning
2020-02-25 12:33:50,587 ERROR Error
2020-02-25 12:33:50,589 FATAL Fatal

在 log4j 的第一个版本中，它是appender 的Threshold 属性。关于如何在 log4j 中解决相同问题，请参阅问题的答案。

在过滤器的帮助下，Log4j2 允许将输出配置到特定的附加程序，比 log4j 更加灵活。