Caused by: org.apache.logging.log4j.LoggingException: log4j-slf4j-impl cannot be present with log4j-to-slf4j

Question

In my Spring boot 2 project:

In build.gradle:

dependencies {
    implementation 'com.google.code.gson:gson:2.7'
    implementation 'com.h2database:h2'
    implementation 'javax.servlet:jstl:1.2'
    implementation 'org.springframework.boot:spring-boot-devtools'
    implementation('org.springframework.boot:spring-boot-starter') {
        exclude group: 'org.springframework.boot', module: 'spring-boot-starter-logging'
    }
    implementation 'org.springframework.boot:spring-boot-starter-actuator'
    implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
    implementation 'org.springframework.boot:spring-boot-starter-log4j2'
    implementation 'org.springframework.boot:spring-boot-starter-jdbc'
    implementation 'org.springframework.boot:spring-boot-starter-security'
    implementation 'org.springframework.boot:spring-boot-starter-thymeleaf'
    implementation "org.springframework.boot:spring-boot-starter-web"

    testImplementation('org.springframework.boot:spring-boot-starter-test') {
        exclude group: 'org.junit.vintage', module: 'junit-vintage-engine'
    }

    testImplementation 'org.junit.jupiter:junit-jupiter:5.5.2'
}

In src/resources/log4j2.xml:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration debug="true" xmlns:log4j="http://jakarta.apache.org/log4j/">

    <appender name="Console"
              class="org.apache.log4j.ConsoleAppender">
        <layout class="org.apache.log4j.PatternLayout">
            <!-- l, L, M - is extremely slow. It's use should be avoided unless execution
                speed is not an issue. -->
            <param name="ConversionPattern"
                   value="%p: %d{dd.MM.yyyy HH:mm:ss.SSS} %l %n    %m%n"/>
        </layout>
    </appender>

    <appender name="File"
              class="org.apache.log4j.DailyRollingFileAppender">
        <param name="Encoding" value="UTF-8"/>
        <param name="File" value="logs/trace.log"/>
        <param name="Append" value="true"/>
        <layout class="org.apache.log4j.PatternLayout">
            <!-- l, L, M - is extremely slow. It's use should be avoided unless execution
                speed is not an issue. -->
            <param name="ConversionPattern"
                   value="%p: %d{dd.MM.yyyy HH:mm:ss.SSS} %l %n    %m%n"/>
        </layout>
    </appender>

    <!-- Application Loggers -->
    <logger name="com.journaldev.spring">
        <level value="info"/>
    </logger>

    <!-- 3rdparty Loggers -->
    <logger name="org.springframework.core">
        <level value="info"/>
    </logger>

    <logger name="org.hibernate">
        <level value="info"/>
    </logger>

    <logger name="org.springframework.beans">
        <level value="info"/>
    </logger>

    <logger name="org.springframework.context">
        <level value="info"/>
    </logger>

    <logger name="org.springframework.web">
        <level value="info"/>
    </logger>

    <!-- The root category is used for all loggers unless a more specific logger
        matches. If none of the loggers are assigned a level, then all loggers inherit
        the level of the root logger which is set to DEBUG by default -->
    <root>
        <level value="ALL"/>
        <appender-ref ref="Console"/>
        <!-- <appender-ref ref="File" /> -->
    </root>

</log4j:configuration>

In my controller:

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;

@Controller
public class CategoryController {
    private CategoryRepository categoryRepository;

    private static Logger logger = LoggerFactory.getLogger(CategoryController.class);

 @GetMapping("/categories")
    public String getCategories(Model model) {
        logger.debug("getCategories>>>>>>>>>>>>>>>>");
        model.addAttribute("categoryList", this.categoryRepository.findAll());
        return "categories/category_list";
    }
}

But when I start project I get error:

Caused by: org.apache.logging.log4j.LoggingException: log4j-slf4j-impl cannot be present with log4j-to-slf4j

Answer 1

According with Spring's documentation (as pointed by Simon), we wave to exclude the "spring-boot-starter-logging" module from all libraries, not only from "spring-boot-starter-web".

configurations {
    ...
    all {
        exclude group: 'org.springframework.boot', module: 'spring-boot-starter-logging'
    }
}

...instead of...

dependencies {
    ...
    implementation('org.springframework.boot:spring-boot-starter') {
        exclude group: 'org.springframework.boot', module: 'spring-boot-starter-logging'
    }
}

Just had myself the same problem and solved with this solution.