Log4j，禁用依赖于环境的 appender

Question

I would like to have one log4j.xml config and be able to log to console while developing my application. Once deployed to an environment I want to only log to a file appender and not the console. How can I achieve this?

This is my current config:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

    <appender name="ConsoleAppender" class="org.apache.log4j.ConsoleAppender">
        <param name="Threshold" value="DEBUG" />
        <param name="Target" value="System.out" />
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern" value="%d{dd-MM-yyyy HH:mm:ss} %-5p%c{1} - %m%n" />
        </layout>
    </appender>

    <appender name="LogFileAppender" class="org.apache.log4j.RollingFileAppender">
        <param name="File" value="${log-base-dir}/${adapter-name}.log" />
        <param name="MaxFileSize" value="5000KB" />
        <param name="MaxBackupIndex" value="99" />
        <param name="append" value="true" />        
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern" value="%d{dd-MM-yyyy HH:mm:ss} %-5p%c{1} - %m%n" />
        </layout>
    </appender>

    <root>
        <level value="info" />
        <appender-ref ref="ConsoleAppender" />
        <appender-ref ref="LogFileAppender" />
    </root>

</log4j:configuration>

Answer 1

One of the solutions could be separation of log4j configuration files for development and production environments eg:

• log4j-development.xml - for development environment
• log4j-production.xml - for production environment

Then your application startup command could have parrameter specifying log4j configuration file eg java -Dlog4jconfig=log4j-development.xml -jar Application.jar

You can configure log4j by getting value of log4jconfig property in your code eg System.getProperty("log4jconfig") .

Pros of that solution are as follows:

• You can specify loggers independently ( ConsoleAppender and LogFileAppender in development and only LogFileAppender in production)
• You can specify your logging level per environment (eg error in production and debug in development)
• You can configure file logger independently eg keep logs for X days in production (for audit purposes etc.) and have only one log file in development etc.

That pattern is used in many application servers where you have multiple environments (Development, UAT, Staging, Production etc.)

Example of log4j-development.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

    <appender name="ConsoleAppender" class="org.apache.log4j.ConsoleAppender">
        <param name="Threshold" value="DEBUG" />
        <param name="Target" value="System.out" />
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern" value="%d{dd-MM-yyyy HH:mm:ss} %-5p%c{1} - %m%n" />
        </layout>
    </appender>

    <root>
        <level value="debug" />
        <appender-ref ref="ConsoleAppender" />
    </root>

</log4j:configuration>

Example of log4j-production.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">

    <appender name="LogFileAppender" class="org.apache.log4j.RollingFileAppender">
        <param name="File" value="${log-base-dir}/${adapter-name}.log" />
        <param name="MaxFileSize" value="5000KB" />
        <param name="MaxBackupIndex" value="99" />
        <param name="append" value="true" />        
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern" value="%d{dd-MM-yyyy HH:mm:ss} %-5p%c{1} - %m%n" />
        </layout>
    </appender>

    <root>
        <level value="error" />
        <appender-ref ref="LogFileAppender" />
    </root>

</log4j:configuration>

Answer 2

It is easy to do using appender's Threshold parameter and JVM system property. Eg

<appender name="CONSOLE" class="org.apache.log4j.ConsoleAppender">
    <param name="Threshold" value="${my.console.level}" />
    <layout class="org.apache.log4j.PatternLayout">
        <param name="ConversionPattern" value="%d %-5p [%c{1}] %m%n" />
    </layout>
</appender>

Then when starting application on prod use -Dmy.console.level=OFF

At the same time when starting locally use -Dmy.console.level=ALL

Both OFF and ALL are valid log4j levels.

Answer 3

With Log4j2 you could alternatively switch the appender reference with a Java system property like so:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="error">
    <Appenders>
        <!-- Log file location uses Tomcat system variable, change for other web servers -->
        <RollingFile name="rolling-file"/>
        <Console name="console"/>
    </Appenders>
    <Loggers>
        <Root level="info">
            <AppenderRef ref="${sys:log4j.loggers.root.appender:-rolling-file}"/>
        </Root>
    </Loggers>
</Configuration>

(the minus - in front of the default value in the sys prop variable is required for some reason)

To switch from the default "rolling-file" to the console"

-Dlog4j.loggers.root.appender=console