Understanding the Exception java.lang.IllegalStateException: Logback configuration error detected

Overview

This article provides a detailed exploration of the exception java.lang.IllegalStateException encountered during the initialization of a logging system in a Spring Boot project configured too use Logback. The example scenario involves replacing Logback with Log4j2 as the logging framework.

Error Details

The stack trace below summarizes the issue:

java.lang.IllegalStateException: Logback configuration error detected: 
ERROR in ch.qos.logback.core.joran.spi.Interpreter@3:16 - no applicable action for [appenders], current ElementPath is [[configuration][appenders]]
...

Upon reviewing the first lines:

Logging system failed to initialize using configuration from 'classpath:log4j2-dev.xml'
java.lang.IllegalStateException: Logback configuration error detected:

It appears the issue stems not from the XML configuration file log4j2-dev.xml directly but from conflicting dependencies in the project's pom.xml setup.

Investigation

Here is the relevant portion of the pom.xml file:

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

Upon closer examination, it's evident that spring-boot-starter-web indirectly includes Logback dependencies, causing conflicts.

Dependency Conflict Diagram

Here is a conceptual dependency diagram:

• Web (spring-boot-starter-web): Includes Logback.
• MyBatis (spring-boot-starter-jdbc): Includes Logback.

These conflict with the explicitly defined Log4j2 dependency spring-boot-starter-log4j2.

Solutions

Resolution Option 1: Exclude Logback Globally

To prevent conflicts, exclude Logback across all dependencies:

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

Resolution Option 2: Targeted Exclusions

For selective exclusions, targeting specific dependencies can also resolve the issue:

<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>

Summary

By examining dependency inclusions and selectively excluding the conflicting spring-boot-starter-logging, issues with the logging initialization processs can be avoided, enabling proper integration of Log4j2 in the Spring Boot application.