Logger not logging to file?

[Suhaas Parekh]

Hello friends,

I am using a root logger to write logs to a file. But file itself is not created.

I have created a maven project. The log4j2.properties file is placed in src/main/resources.

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.trial</groupId>
  <artifactId>log4j</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <name>log4j</name>
  <dependencies>
  
  <dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-api</artifactId>
    <version>2.11.1</version>
  </dependency>
  <dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
    <version>2.11.1</version>
  </dependency>
  <!-- https://mvnrepository.com/artifact/log4j/log4j -->

  </dependencies>
</project>

Log4jDemo.java

package com.trial.log4j;


import org.apache.logging.log4j.Logger;

import org.apache.logging.log4j.LogManager;

public class Log4jDemo {
	 
	static Logger logger=LogManager.getLogger(Log4jDemo.class);
	
	public static void main(String[] args) {
		logger.debug("debug");

		logger.info("info");
		logger.error("error");

		logger.warn("warn");

		logger.fatal("fatal");

	}
}

log4j2.properties

# Define the root logger with appender file
log4j.rootLogger = DEBUG, FILE

# Define the file appender
log4j.appender.FILE=org.apache.log4j.FileAppender

# Set the name of the file
log4j.appender.FILE.File=log.out

# Set the immediate flush to true (default)
log4j.appender.FILE.ImmediateFlush=true

# Set the threshold to debug mode
log4j.appender.FILE.Threshold=debug

# Set the append to false, overwrite
log4j.appender.FILE.Append=false

# Define the layout for file appender
log4j.appender.FILE.layout=org.apache.log4j.PatternLayout
log4j.appender.FILE.layout.conversionPattern=%m%n

[Paul Clapham]

I would suggest providing the full path to the log file. Using a relative path could lead to confusion.

And I don't understand the append/overwrite distinction... it looks to me like every time you write an entry to the log file, you're going to overwrite the previous entry. But that's probably just me not understanding what the distinction is for and why it even exists.

[Campbell Ritchie]

Overwrite probably means you only find the most recent exception in the log file. Append probably means your log file is (approx.) 375693875983275936453 lines long

[Rob Spoor]

Unrelated, but do yourself a favour and update the Log4J version to 2.17.1 as soon as you can. That's basically the only secure version since ever. With the version you're using, you're highly vulnerable for a number of vulnerabilities, with Log4Shell the worst of the bunch.

[Tim Holloway]

"Append" means keep the existing log file and add onto the end when you run the app. No problem with that as long as you do make sure that it doesn't get forgotten and grow until it eats your disk.

I'll confirm Paul's other suggestion. It's quite hazardous to use a relative path for a logfile. It's entirely possible that the log was actually created, but you don't know where!