Log4J log file remains empty when configuring programmatically

I'm trying to configure Log4J programmatically to write the logs to both the console and to a log file. While the console output looks fine, the log file remains empty (but is created though). I'm using OpenJDK 22 on Zorin 17.1 Core.

Why is that and how to fix it?

Here's a minimal working example that resembles the issue in my actual project:

import org.apache.logging.log4j.Level;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.core.Filter;
import org.apache.logging.log4j.core.appender.ConsoleAppender;
import org.apache.logging.log4j.core.config.Configurator;
import org.apache.logging.log4j.core.config.LoggerConfig;
import org.apache.logging.log4j.core.config.builder.api.AppenderComponentBuilder;
import org.apache.logging.log4j.core.config.builder.api.ConfigurationBuilder;
import org.apache.logging.log4j.core.config.builder.api.ConfigurationBuilderFactory;
import org.apache.logging.log4j.core.config.builder.impl.BuiltConfiguration;

public class Main {
    public static void main(String[] args) {
        Level level = Level.WARN;

        ConfigurationBuilder<BuiltConfiguration> builder = ConfigurationBuilderFactory.newConfigurationBuilder();
        builder.setStatusLevel(level);
        builder.setConfigurationName("BuilderTest");

        AppenderComponentBuilder appenderBuilder =
            builder.newAppender("Stdout", "CONSOLE")
                .addAttribute("target", ConsoleAppender.Target.SYSTEM_OUT)
                .add(builder.newLayout("PatternLayout")
                .addAttribute("pattern", "xxxxx %d [%t] %-5level: %msg%n%throwable"))
                .add(builder.newFilter("MarkerFilter", Filter.Result.DENY, Filter.Result.NEUTRAL)
                .addAttribute("marker", "FLOW"));

        builder.add(appenderBuilder);

        appenderBuilder =
            builder.newAppender("File", "File")
            .addAttribute("fileName", "logs/main.log")
            .addAttribute("append", true)
            .addAttribute("locking", false)
            .addAttribute("immediateFlush", true)
            .add(builder.newLayout("PatternLayout")
            .addAttribute("pattern", "xxxxxx %d [%t] %-5level: %msg%n%throwable"));

        builder.add(appenderBuilder);

        builder
            .add(builder.newLogger("org.apache.logging.log4j", level)
            .add(builder.newAppenderRef("Stdout"))
            .addAttribute("additivity", false));

        builder.add(
            builder
                .newRootLogger(level)
                .add(builder.newAppenderRef("Stdout"))
        );

        Configurator.reconfigure(builder.build());
        LoggerConfig loggerConfig = new LoggerConfig(Main.class.getPackageName(), level, false);
        Configurator.setLevel(Main.class.getPackageName(), level);

        LogManager.getRootLogger().error("setLoggingLevel(): Logging level set to %s.".formatted(level));
    }
}

Console output:

xxxxx 2024-08-30 01:43:22,830 [main] ERROR: setLoggingLevel(): Logging level set to WARN.

Here's my pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example.log4j-test</groupId>
    <artifactId>log4j-test</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>22</maven.compiler.source>
        <maven.compiler.target>22</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        <dependency>
            <groupId>commons-logging</groupId>
            <artifactId>commons-logging</artifactId>
            <version>1.3.4</version>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-api</artifactId>
            <version>3.0.0-beta2</version>
        </dependency>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>3.0.0-beta2</version>
        </dependency>
    </dependencies>
</project>

Solution

Project Tree

├── pom.xml
└── src
    └── main
        └── java
            └── com
                └── example
                    └── Main.java

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://maven.apache.org/POM/4.0.0"
         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.example.log4j-test</groupId>
    <artifactId>log4j-test</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>17</maven.compiler.source>
        <maven.compiler.target>17</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <!--
        <log4j2.version>2.19.0</log4j2.version>
        -->
        <log4j2.version>3.0.0-beta2</log4j2.version>
    </properties>

    <dependencies>

        <!-- Log4j2 core -->
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>${log4j2.version}</version>
        </dependency>

        <!-- Log4j2 API -->
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-api</artifactId>
            <version>${log4j2.version}</version>
        </dependency>

    </dependencies>

</project>

Main.java

package com.example;

import org.apache.logging.log4j.Level;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.core.config.Configurator;
import org.apache.logging.log4j.core.config.builder.api.*;
import org.apache.logging.log4j.core.config.builder.impl.BuiltConfiguration;

public class Main {

    //private static final Logger logger = LogManager.getLogger(Main.class);
    //private static final Logger appLoggerInstance = LogManager.getLogger("com.example");
    
    public static void main(String[] args) {
    

    
        // Create a ConfigurationBuilder instance
        ConfigurationBuilder<BuiltConfiguration> builder = ConfigurationBuilderFactory.newConfigurationBuilder();
        builder.setStatusLevel(Level.WARN);
    
        // Create a pattern layout
        
        String pattern1 = "XXXX %d [%t] %-5level: %msg%n%throwable";
        String pattern2 = "%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n";
        
        LayoutComponentBuilder layout = builder.newLayout("PatternLayout")
                .addAttribute("pattern", pattern1 );

        // Create Console Appender
        AppenderComponentBuilder consoleAppender = builder.newAppender("Stdout", "Console")
                .addAttribute("target", "SYSTEM_OUT")
                .add(layout);

        // Create File Appender
        AppenderComponentBuilder fileAppender = builder.newAppender("File", "File")
                .addAttribute("fileName", "logs/main.log")
                .addAttribute("append", true)
                .addAttribute("locking", false)
                .addAttribute("immediateFlush", true)                
                .add(layout);

        // Add appenders to the configuration
        builder.add(consoleAppender);
        builder.add(fileAppender);

        // Root Logger configuration
        RootLoggerComponentBuilder rootLogger = builder.newRootLogger("info");
        rootLogger.add(builder.newAppenderRef("Stdout"));
        rootLogger.add(builder.newAppenderRef("File"));
        builder.add(rootLogger);

        // Application-specific Logger configuration
        LoggerComponentBuilder appLogger = builder.newLogger("com.example", "debug")
                .add(builder.newAppenderRef("Stdout"))
                .add(builder.newAppenderRef("File"))
                .addAttribute("additivity", false);

        // Add logger to the configuration
        builder.add(appLogger);

        // Apply the configuration
        Configurator.initialize(builder.build());

        // Test logging
        Logger logger = LogManager.getLogger(Main.class);
        logger.info("This is an info message from the root logger.");
        logger.debug( "This is a debug message from the root logger.");
        logger.error( "This is an error message from the root logger.");
        
        Logger appLoggerInstance = LogManager.getLogger("com.example");
        appLoggerInstance.debug("ZZZ This is a debug message from com.example logger.");
        
        LogManager.getRootLogger().error("setLoggingLevel(): Logging level set to %s.".formatted(Level.WARN));
    }
}

log4j2.xml

The program does not use log4j2.xml, but our program code can use log4j2.xml as a baseline conversion mapping.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
    <Appenders>
        <!-- Console Appender Configuration -->
        <Console name="Stdout" target="SYSTEM_OUT">
            <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n"/>
        </Console>

        <!-- File Appender Configuration -->
        <File name="File" fileName="logs/app-log4j-xml.log" append="true">
            <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n"/>
        </File>
    </Appenders>

    <Loggers>
        <!-- Root Logger Configuration -->
        <Root level="info">
            <AppenderRef ref="Stdout"/>
            <AppenderRef ref="File"/>
        </Root>

        <!-- Application Specific Logger Configuration -->
        <Logger name="com.example" level="debug" additivity="false">
            <AppenderRef ref="Stdout"/>
            <AppenderRef ref="File"/>
        </Logger>
    </Loggers>
</Configuration>

Build And Run

mvn clean package

mvn dependency:copy-dependencies -DoutputDirectory=target/libs

java -cp "target/libs/*:target/log4j-test-1.0-SNAPSHOT.jar" com.example.Main

Result:

XXXX 2024-08-30 09:20:01,980 [main] INFO : This is an info message from the root logger.
XXXX 2024-08-30 09:20:02,002 [main] DEBUG: This is a debug message from the root logger.
XXXX 2024-08-30 09:20:02,002 [main] ERROR: This is an error message from the root logger.
XXXX 2024-08-30 09:20:02,003 [main] DEBUG: ZZZ This is a debug message from com.example logger.
XXXX 2024-08-30 09:20:02,003 [main] ERROR: setLoggingLevel(): Logging level set to WARN.

Mapping log4j2.xml to code

Configuration status

<Configuration status="WARN">

builder.setStatusLevel(Level.WARN);

PatternLayout

<PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n"/>

// Create a pattern layout

String pattern1 = "XXXX %d [%t] %-5level: %msg%n%throwable";
String pattern2 = "%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n";

LayoutComponentBuilder layout = builder.newLayout("PatternLayout")
        .addAttribute("pattern", pattern1 );

Console Appender

<!-- Console Appender Configuration -->
<Console name="Stdout" target="SYSTEM_OUT">
    <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n"/>
</Console>

// Create Console Appender
AppenderComponentBuilder consoleAppender = builder.newAppender("Stdout", "Console")
        .addAttribute("target", "SYSTEM_OUT")
        .add(layout);

File Appender

The code is inconsistent with xml. Adjust the code to be consistent with the program described in the problem.

<!-- File Appender Configuration -->
<File name="File" fileName="logs/app-log4j-xml.log" append="true">
    <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n"/>
</File>

// Create File Appender
AppenderComponentBuilder fileAppender = builder.newAppender("File", "File")
        .addAttribute("fileName", "logs/main.log")
        .addAttribute("append", true)
        .addAttribute("locking", false)
        .addAttribute("immediateFlush", true)                
        .add(layout);

Add Appenders

// Add appenders to the configuration
builder.add(consoleAppender);
builder.add(fileAppender);

Root Logger

<!-- Root Logger Configuration -->
<Root level="info">
    <AppenderRef ref="Stdout"/>
    <AppenderRef ref="File"/>
</Root>

// Root Logger configuration
RootLoggerComponentBuilder rootLogger = builder.newRootLogger("info");
rootLogger.add(builder.newAppenderRef("Stdout"));
rootLogger.add(builder.newAppenderRef("File"));
builder.add(rootLogger);

App Logger

<!-- Application Specific Logger Configuration -->
<Logger name="com.example" level="debug" additivity="false">
    <AppenderRef ref="Stdout"/>
    <AppenderRef ref="File"/>
</Logger>

// Application-specific Logger configuration
LoggerComponentBuilder appLogger = builder.newLogger("com.example", "debug")
        .add(builder.newAppenderRef("Stdout"))
        .add(builder.newAppenderRef("File"))
        .addAttribute("additivity", false);
        
// Add logger to the configuration
builder.add(appLogger);