Why Your logback-spring.xml Isn’t Working and How to Fix It

Background

Recently a teammate reported that the logback-spring.xml file was not taking effect. Because the author had not created a new application for a long time, the configuration details were unfamiliar, leading to a lengthy investigation.

Logback Overview

SLF4J (Simple Logging Facade for Java) provides a unified logging API, while Logback is a logging implementation that integrates seamlessly with SLF4J and can replace it.

Logback Configuration

Pandora‑boot includes Logback by default, so no additional Logback dependency is required.

Configuration Approach

The official recommendation is to use Logback, and the troubleshooting steps focus on Logback not taking effect.

Specify Configuration File Path

In application.properties add:

logging.config=classpath:logback-spring.xml

Custom Configuration File

<?xml version="1.0" encoding="UTF-8"?>
<configuration scan="true">
    <!-- defaults.xml from Spring Boot -->
    <include resource="org/springframework/boot/logging/logback/defaults.xml" />
    <property name="APP_NAME" value="xxxx" />
    <property name="LOG_PATH" value="${user.home}/logs/eleme/${APP_NAME}/" />
    <property name="LOG_FILE" value="${LOG_PATH}/application.log" />
    <property name="ERROR_LOG_FILE" value="${LOG_PATH}/common-error.log"/>
    <property name="TRACE_FILE_LOG_PATTERN" value="[%X{requestId}][%X{rpcId}] -%green(%d{yyyy-MM-dd HH:mm:ss.SSS}) ${LOG_LEVEL_PATTERN:-%5p} %magenta(${PID:- }) --- [%t] %-40.40logger{39} : %m%n${LOG_EXCEPTION_CONVERSION_WORD:-%wEx}"/>
    <property name="ERROR_FILE_LOG_PATTERN_D" value="${ERROR_FILE_LOG_PATTERN_D:-%d{yyyy-MM-dd HH:mm:ss.SSS} ${LOG_LEVEL_PATTERN:-%5p} [%X{requestId}] [%X{rpcId}][traceId:%X{EAGLEEYE_TRACE_ID}][%c{2}#%M] %logger{39} : %m%n${LOG_EXCEPTION_CONVERSION_WORD:-%wEx}}"/>
    <appender name="APPLICATION" class="ch.qos.logback.core.rolling.RollingFileAppender">
        <file>${LOG_FILE}</file>
        <encoder>
            <pattern>${TRACE_FILE_LOG_PATTERN}</pattern>
        </encoder>
        <rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
            <fileNamePattern>${LOG_FILE}.%d{yyyy-MM-dd}.%i.log</fileNamePattern>
            <maxHistory>7</maxHistory>
            <maxFileSize>50MB</maxFileSize>
            <totalSizeCap>20GB</totalSizeCap>
        </rollingPolicy>
    </appender>
    <appender name="ERROR_APPENDER" class="ch.qos.logback.core.rolling.RollingFileAppender">
        <file>${ERROR_LOG_FILE}</file>
        <encoder>
            <pattern>${ERROR_FILE_LOG_PATTERN_D}</pattern>
        </encoder>
        <rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
            <fileNamePattern>${ERROR_LOG_FILE}.%d{yyyy-MM-dd}.%i.log</fileNamePattern>
            <maxHistory>7</maxHistory>
            <maxFileSize>50MB</maxFileSize>
            <totalSizeCap>20GB</totalSizeCap>
        </rollingPolicy>
        <filter class="ch.qos.logback.classic.filter.LevelFilter">
            <level>ERROR</level>
            <onMatch>ACCEPT</onMatch>
            <onMismatch>DENY</onMismatch>
        </filter>
    </appender>
    <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>${TRACE_CONSOLE_LOG_PATTERN}</pattern>
            <charset>utf8</charset>
        </encoder>
    </appender>
    <root level="INFO">
        <appender-ref ref="APPLICATION" />
        <appender-ref ref="ERROR_APPENDER" />
    </root>
</configuration>

Potential Configuration Issues

1) Custom variables not taking effect? Only a few built‑in variables (${PID}, ${LOG_FILE}, ${LOG_PATH}, ${LOG_EXCEPTION_CONVERSION_WORD}) work directly; others must be defined as <property> entries, e.g., APP_NAME .

2) Want more error details? Add the JVM option -Dlog4j.defaultInitOverride=true when starting the application.

Symptoms After Configuration

After applying the configuration, custom appenders may still be ignored, and logs are only written to service_stdout.log. This is because the startup script start_pandora_boot forces output to $SERVICE_OUT, overriding the custom logback-spring.xml settings.

Analysis of Non‑functionality

Remote Debugging

Enable remote debug with

JPDA_OPTS="-agentlib:jdwp=transport=$JPDA_TRANSPORT,address=$JPDA_ADDRESS,server=y,suspend=$JPDA_SUSPEND"

Start IDEA Remote JVM Debug session.

Inspecting Logback Appender

Run LoggerFactory.getLogger("ROOT") and examine the ROOT logger. The custom appender defined in logback-spring.xml may be missing, indicating it was overridden or given lower priority.

Investigating Log Conflicts

Exclude SLF4J-Log4j12 when using Logback.

Remove jcl-over-slf4j and commons-logging to avoid classpath conflicts.

Use a Dependency Analyzer to quickly locate and exclude conflicting artifacts.

Double‑Check

Run LoggerFactory.getLogger("ROOT") again and verify that the custom appender and file are correctly initialized.

Conclusion

1) Read the Spring Boot documentation carefully; the pitfalls described are not unique.

2) When adding third‑party libraries, follow the principle of minimal inclusion and use exclusion to prevent transitive conflicts.