Show log4j messages in run output

[Dom1]

Hi,

I have an issue when running JAR jobs. I expect to see logs in the output window of a run. Unfortunately, I can only see messages of that are generated with "System.out.println" or "System.err.println". Everything that is logged via slf4j is only shown in the log4j-Logs of the cluster. 

Is there a way to show the logs of slf4j in the output window of the executed run? When we log in python then those logs are shown, so I hope that this is also possible for Java code.

Thanks for your help

Dominik 

[Kaniz_Fatma]

Hi @Dom1, 

• Ensure that both the slf4j-api and exactly one implementation binding (such as slf4j-simple, logback...¹.
• If you’re developing a library, it’s recommended to depend only on slf4j-api and let the users of your library choose the actual logging implementation.
• To capture SLF4J logs in the output window during a Gradle build, add the following line to your build script:

  logging.captureStandardOutput LogLevel.INFO
  

• Run your build with the -i flag to see the captured logs
• In your Java code, ensure that you’re using SLF4J for logging.
• Use the appropriate logger (e.g., LoggerFactory.getLogger(MyClass.class)) to log messages.

Happy logging! 😊🚀!

[Dom1]

Hi @Kaniz_Fatma 

thanks for your response. I just build a minimal project that looks like this:

package logging;

import lombok.extern.slf4j.Slf4j;

@Slf4j
public class TestLogging {

	public static void main(String[] args) {
		log.trace("Test: Trace message");
		log.debug("Test: Debug message");
		log.info("Test: Info message");
		log.info("Test: New test with log4j2");
		log.warn("Test: Warning message");
		log.error("Test: Error message");
	}
}

So just a simple main method that logs on different levels. My pom dependencies look like this:

	<dependencies>

		<dependency>
			<groupId>org.apache.logging.log4j</groupId>
			<artifactId>log4j-api</artifactId>
			<version>2.23.1</version>
		</dependency>

		<dependency>
			<groupId>org.apache.logging.log4j</groupId>
			<artifactId>log4j-core</artifactId>
			<version>2.23.1</version>
		</dependency>

		<dependency>
			<groupId>org.apache.logging.log4j</groupId>
			<artifactId>log4j-slf4j2-impl</artifactId>
			<version>2.23.1</version>
		</dependency>

		<dependency>
			<groupId>org.slf4j</groupId>
			<artifactId>slf4j-api</artifactId>
			<version>2.0.12</version>
		</dependency>

		<dependency>
			<groupId>org.projectlombok</groupId>
			<artifactId>lombok</artifactId>
			<version>1.18.30</version>
			<scope>provided</scope>
		</dependency>
	</dependencies>

And here my log4j2.xml file

<?xml version="1.0" encoding="UTF-8"?>
<Configuration>
	<Appenders>

		<Console name="console" target="SYSTEM_OUT">
			<PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss} [%thread] %-5level %logger{36} - %msg%n" />
		</Console>

	</Appenders>
	<Loggers>
		<Root level="INFO">
			<AppenderRef ref="console" />
		</Root>
	</Loggers>
</Configuration>

When I run this on my local machine, then it shows the following logs 

2024-04-18 14:33:00 [main] INFO  logging.TestLogging - Test: Info message
2024-04-18 14:33:00 [main] INFO  logging.TestLogging - Test: New test with log4j2
2024-04-18 14:33:00 [main] WARN  logging.TestLogging - Test: Warning message
2024-04-18 14:33:00 [main] ERROR logging.TestLogging - Test: Error message

But when I package this as a jar, upload it to databricks and run the code then it does not print anything in the output window of the task. I see some logs in the Log4j output of the cluster but with a different logging pattern:

24/04/18 12:24:10 INFO TestLogging: Test: Info message
24/04/18 12:24:10 INFO TestLogging: Test: New test with log4j2
24/04/18 12:24:10 WARN TestLogging: Test: Warning message
24/04/18 12:24:10 ERROR TestLogging: Test: Error message

So I assume the logging settings of my jar is replaced somewhere. I don´t know how I can show the log messages into the output of the task run (or redirect them into one file for this specific run).

Hope the examples show what I am trying to accomplish 😉