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I am having a problem with log4j --- I am trying to set the logging level to DEBUG with a log4j.properties file. I know that this partially works because another component (netty ) works but by the time it gets to me logging is set to ERROR and above.

Here is my log4j.properties file:

#Define root logger options log4j.rootLogger=DEBUG, console log4j.logger.com.ltsllc.miranda=DEBUG #Define console appender log4j.appender.console=org.apache.log4j.ConsoleAppender log4j.appender.console.Target=System.out log4j.appender.console.layout=org.apache.log4j.PatternLayout log4j.appender.console.layout.ConversionPattern=%-5p %c{1} - %m%n

here is the code that checks the debugging level:

 if (l.isDebugEnabled()) { l.debug("DEBUG is enabled"); } else { l.error ("Debug is disabled"); l.error ("level is: " + l.getLevel()); }

here is the output:

DEBUG ResourceLeakDetector - -Dio.netty.leakDetection.level: simple DEBUG ResourceLeakDetector - -Dio.netty.leakDetection.targetRecords: 4 DEBUG ResourceLeakDetectorFactory - Loaded default ResourceLeakDetector: io.netty.util.ResourceLeakDetector@44b3606b 22:43:46.696 \[main\] ERROR com.ltsllc.miranda.Miranda - Debug is disabled 22:43:46.700 \[main\] ERROR com.ltsllc.miranda.Miranda - level is: ERROR DEBUG DefaultChannelId - -Dio.netty.processId: 30572 (auto-detected) DEBUG NetUtil - -Djava.net.preferIPv4Stack: false

I expected something like this

DEGUG com.ltsllc.miranda.Miranda - DEBUG is enabled
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2 Answers 2

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When no configuration is provided the Log4j2 Reference Implementation (log4j-core) uses a %d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n pattern and an ERROR level. This is what you are observing on your standard output.

The logging APIs and backends are probably bound as follows:

  • Netty's internal logging API (cf. InternalLoggerFactory) binds to SLF4J (slf4j-api), which uses Log4j 1.x or Reload4j as backend. This backend is the one you configured.
  • the Log4j2 API you use in your code(cf. API separation) binds to Log4j2 Reference Implementation, which you didn't configure. I am guessing that the fully qualified class name of l in your code is org.apache.logging.log4j.Logger.

I am assuming you don't want to use Log4j 1.x as backend (it was declared end-of-life 8 years ago) so you need to:

  1. Configure log4j-core by adding a log4j2.xml file with content: 
    <Configuration> <Appenders> <Console name="console"> <PatternLayout pattern="%-5p %c{1} - %m%n"/> </Console> </Appenders> <Loggers> <Root level="DEBUG"> <AppenderRef ref="console"/> </Root> </Loggers> </Configuration>
  2. Fix up your dependencies, by:
    • Removing the log4j:log4j and ch.qos.reload4j:reload4j artifacts from your classpath. This also includes the SLF4J bindings org.slf4j:slf4j-log4j12 and org.slf4j:slf4j-reload4j.
    • Netty binds to Log4j2 API if SLF4J (slf4j-api) is not present, but other libraries might be using SLF4J directly. If you are using Maven you need these 3 artifacts: 
       <dependencyManagement> <!-- Add the BOM, so you don't need to specify version --> <dependencies> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-bom</artifactId> <version>2.20.0</version> <scope>import</scope> <type>pom</type> </dependency> </dependencies> </dependencyManagement> <dependencies> <!-- Used in your code --> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-api</artifactId> </dependency> <!-- Only necessary at runtime --> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-core</artifactId> <scope>runtime</scope> </dependency> <!-- ~ If some of your libraries use SLF4J API directly ~ bind them to `log4j-api`: --> <dependency> <groupId>org.apache.logging.log4j</groupId> <!-- Replace with log4j-slf4j2-impl if SLF4J 2.x is used --> <artifactId>log4j-slf4j-impl</artifactId> <scope>runtime</scope> </dependency> </dependencies>
      If your libraries use other logging APIs (e.g. Jakarta Apache Commons Logging, java.util.logging, JBoss Logging), you'll also need to bind them to log4j-api.

Edit: I would advise against using the properties configuration format for Log4j 2.x, since it is extremely verbose to store a tree-like structure in a flat format. Besides when Log4j 1.x was released the JRE did not have an XML parser, now it has it.

The XML configuration above can be translated to properties as:

appender.0.type = Console appender.0.name = console appender.0.0.type = PatternLayout appender.0.0.pattern = %-5p %c{1} - %m%n logger.rootLogger.level = DEBUG logger.rootLogger.appenderRef.0.ref = console ## # The `rootLogger` config can be abbreviated in recent versions to # logger.rootLogger = DEBUG, console
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My maven could not find log4j-slf4j2-impl. Please let me know what (which version of maven) you tried this with.
Also --- could you restate the changes in log4j.xml as properties for log4j.properties?
@ClarkHobbie: log4j-slf4j2-impl is available since version 2.19.0 (cf. MvnRepository) (first version after the release of SLF4J 2.x).
I added a properties configuration to the answer. Remark that the autodetected configuration files in Log4j 2.x must start with log4j2 (notice the 2): log4j2.xml or log4j2.properties.
The version of maven that comes with IDEA cannont resolve this dependency: <dependency> <groupId>org.apache.logging.log4j</groupId> <!-- Replace with log4j-slf4j2-impl if SLF4J 2.x is used --> <artifactId>log4j-slf4j-impl</artifactId> <scope>runtime</scope> </dependency> I integrated your other changes and it still doesn't work.
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I found the answer in a question relating to how to set the logging level programmatically:

LoggerContext ctx = (LoggerContext) LogManager.getContext(false); Configuration config = ctx.getConfiguration(); LoggerConfig loggerConfig = config.getLoggerConfig(LogManager.ROOT_LOGGER_NAME); loggerConfig.setLevel(level); ctx.updateLoggers(); // This causes all Loggers to refetch information from their LoggerConfig.

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