How to correctly use log4j2 in Spring Boot application

Question

I wanted to include log4j2 for the logging purpose in my application only. So I included the following dependency in the pom.xml of my project:

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-log4j2</artifactId>
        </dependency>

But at the start of the application I get the following exceptions :

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/C:/m2repo/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/C:/m2repo/org/apache/logging/log4j/log4j-slf4j-impl/2.12.1/log4j-slf4j-impl-2.12.1.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [ch.qos.logback.classic.util.ContextSelectorStaticBinder]

On researching more about it on many platforms I found an approach to exclude logback dependency as I thought I need to use the log4j2.But after excluding that jar also I get the following error:

Exception in thread "main" java.lang.ExceptionInInitializerError
Caused by: org.apache.logging.log4j.LoggingException: log4j-slf4j-impl cannot be present with log4j-to-slf4j

So for solving that: I excluded the log4j-to-slf4j dependency also.

And finally it starts working but now I see a ton of log messages which are more related to Spring boot Internal. For instance :

2019-12-05 12:05:01.649 [DEBUG]  [restartedMain] - Included patterns for restart : []
2019-12-05 12:05:01.649 [DEBUG]  [restartedMain] - Excluded patterns for restart : [/spring-boot-actuator/target/classes/, /spring-boot-devtools/target/classes/, /spring-boot/target/classes/, /spring-boot-starter-[\w-]+/, /spring-boot-autoconfigure/target/classes/, /spring-boot-starter/target/classes/]
2019-12-05 12:05:01.649 [INFO ]  [restartedMain] - Devtools property defaults active! Set 'spring.devtools.add-properties' to 'false' to disable
2019-12-05 12:05:01.649 [DEBUG]  [restartedMain] - Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@3883fd6d
2019-12-05 12:05:01.666 [DEBUG]  [restartedMain] - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalConfigurationAnnotationProcessor'
2019-12-05 12:05:01.686 [DEBUG]  [restartedMain] - Creating shared instance of singleton bean 'org.springframework.boot.autoconfigure.internalCachingMetadataReaderFactory'
2019-12-05 12:05:02.037 [DEBUG]  [restartedMain] - Creating shared instance of singleton bean 'propertySourcesPlaceholderConfigurer'
2019-12-05 12:05:02.043 [DEBUG]  [restartedMain] - Creating shared instance of singleton bean 'org.springframework.boot.context.properties.ConfigurationPropertiesBeanDefinitionValidator'
2019-12-05 12:05:02.055 [DEBUG]  [restartedMain] - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerProcessor'
2019-12-05 12:05:02.056 [DEBUG]  [restartedMain] - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerFactory'
2019-12-05 12:05:02.059 [DEBUG]  [restartedMain] - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalAutowiredAnnotationProcessor'

My pom.xml is like :

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.0.RELEASE</version>
        <relativePath /> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.log4j2</groupId>
    <artifactId>log4j2-check</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>log4j2-check</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>ch.qos.logback</groupId>
                    <artifactId>logback-classic</artifactId>
                </exclusion>
                <exclusion>
                    <groupId>org.apache.logging.log4j</groupId>
                    <artifactId>log4j-to-slf4j</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-log4j2</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

also log4j2 properties like :

name=PropertiesConfig
property.filename = Test
appenders = console
appender.console.type = Console
appender.console.name = STDOUT
appender.console.layout.type = PatternLayout
appender.console.layout.pattern = %d{yyyy-MM-dd HH:mm:ss.SSS} [%-5level]  [%t] - %msg%n
rootLogger.level = debug
rootLogger.appenderRefs = STDOUT
rootLogger.appenderRef.stdout.ref = STDOUT

How can or what are correct configurations needed to use log4j2 only for application purposes and not for Spring boot.

Archfiend

If you only want to log your application at debug then set the root logger level to warn and then add a logger for the package space that your application uses and set that to debug. – Boylan

Answer 1

So I identified the issue which triggered the printing of unexpected messages from spring boot. From the log4j2 configuration I had set the following

rootLogger.level = debug

This property makes the log4j2 to print all the internal messages of spring boot set to debug mode also to print.

Changing it to following :

rootLogger.level = info

solves the issue.

Now the application prints only those loggers whose level is greater than info. So now, it does not print unwanted log messages.

I would say it was not an issue, log4j2 was working correct but my configuration settings were not correct as per my requirements.

Archfiend

Answer 2

I believe this is because log4j2 loggers handling spring boot internal files are included into your configuration.

Take a look here - this are relevant definitions.

Technically I'm not really familiar with log2j2 but it seems that it supports xInclude directive

Acculturize