Log4j2 with SpringBoot (configuration)

September 9, 2022

I did read other questions, also I’ve read configuration and I came up with a solution but I don’t know if it’s okay.

Problem: I have SpringBoot application and I was trying to use log4j2 as logging framework but I couldn’t configure it properly. I had correct xml configuration, configuration was on a classpath but I was able to log only these 4 log levels:
INFO, WARN, ERROR and FATAL

By log4j2 documentation, if configuration is not found, default configuration is used and that configuration display only ERROR and FATAL, but mine app was showing 4 log levels as I wrote earlier. I found that behavior bizarre so I kept reading articles and I came up with this solution.

I replaced these 3 dependencies:

<dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
        <groupId>org.apache.logging.log4j</groupId>
        <artifactId>log4j-core</artifactId>
        <version>${log4j2.version}</version>
</dependency>
<dependency>
        <groupId>org.apache.logging.log4j</groupId>
        <artifactId>log4j-api</artifactId>
        <version>${log4j2.version}</version>
</dependency>

With these 2:

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
        <exclusions>
          <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-logging</artifactId>
          </exclusion>
        </exclusions>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-log4j2</artifactId>
    </dependency>

And it works, but it feels wrong. By excluding spring-boot-starter-logging my log4j2.xml has power again.

This is my (log4j2) XML file:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN" monitorInterval="30">
  <Properties>
    <Property name="LOG_PATTERN">%d{yyyy-MM-dd'T'HH:mm:ss.SSSZ} %p %m%n</Property>
    <Property name="APP_LOG_ROOT">c:/temp</Property>
  </Properties>
  <Appenders>
    <Console name="Console" target="SYSTEM_OUT" follow="true">
      <PatternLayout pattern="${LOG_PATTERN}" />
    </Console>
 
    <RollingFile name="appLog"
      fileName="${APP_LOG_ROOT}/SpringBoot2App/application.log"
      filePattern="${APP_LOG_ROOT}/SpringBoot2App/application-%d{yyyy-MM-dd}-%i.log">
      <PatternLayout pattern="${LOG_PATTERN}" />
      <Policies>
        <SizeBasedTriggeringPolicy size="19500KB" />
      </Policies>
      <DefaultRolloverStrategy max="1" />
    </RollingFile>
 
  </Appenders>
  <Loggers>
 
    <Logger name="com.howtodoinjava.app" additivity="false">
      <AppenderRef ref="appLog" />
      <AppenderRef ref="Console" />
    </Logger>
 
    <Root level="debug">
      <AppenderRef ref="Console" />
    </Root>
  </Loggers>
</Configuration>

And java class:

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class MyApp{
    private static final Logger logger = LogManager.getLogger(MyApp.class);
    public static void main(String[] args) {
        SpringApplication.run(MyApp.class, args);
         
         logger.fatal("HoHoHo FATAL");
         logger.debug("HoHoHo DEBUG");
         logger.trace("HoHoHo TRACE");
         logger.info("HoHoHo INFO");
         logger.warn("HoHoHo WARN");
         logger.error("HoHoHo ERROR");
    }
}

So now if I set Root level="trace" in my log4j2.xml file, I will see all these HoHoHo logs in a console which is what I want. If I set Root level="error" I will see only error and fatal which is also okay. However, I noticed that by changing these levels logs, my application shows a bit different logs while starting so I’m not sure if that is okay or not.. I’m wondering if I configured everything the way it should be configured.

These 2 images are showing what is different when I change log levels between trace and error.

So in one example I have ~1150 lines and with other approach I have ~1200 and they’re mostly identical besides this. And as you can see, when I use trace as logging level, my application doesn’t start with Spring drawing on a first line in a console.

Sorry if post is too long or unclear, so I’ll wrap my question up once again in one sentence. Did I configure my log4j2 correctly (check 2 dependencies I’m using instead of 3 that I removed). Thanks!