claude-dev-suite Logback - Quick Reference
When to Use This Skill
- Configure logging in Spring Boot/Java applications
- File appender with rotation
- High-performance async logging
Deep Knowledge: Use
mcp__documentation__fetch_docswith technology:logbackfor comprehensive documentation.
Configuration
logback-spring.xml (Spring Boot)
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<include resource="org/springframework/boot/logging/logback/defaults.xml"/>
<property name="LOG_PATH" value="${LOG_PATH:-logs}"/>
<property name="LOG_FILE" value="${LOG_FILE:-app}"/>
<!-- Console Appender -->
<appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
<encoder>
<pattern>%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){faint} %clr(${LOG_LEVEL_PATTERN:-%5p}) %clr(${PID:- }){magenta} %clr(---){faint} %clr([%15.15t]){faint} %clr(%-40.40logger{39}){cyan} %clr(:){faint} %m%n${LOG_EXCEPTION_CONVERSION_WORD:-%wEx}</pattern>
</encoder>
</appender>
<!-- Rolling File Appender -->
<appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
<file>${LOG_PATH}/${LOG_FILE}.log</file>
<rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
<fileNamePattern>${LOG_PATH}/${LOG_FILE}.%d{yyyy-MM-dd}.%i.log.gz</fileNamePattern>
<maxFileSize>100MB</maxFileSize>
<maxHistory>30</maxHistory>
<totalSizeCap>3GB</totalSizeCap>
</rollingPolicy>
<encoder>
<pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
</encoder>
</appender>
<!-- Async Appender -->
<appender name="ASYNC" class="ch.qos.logback.classic.AsyncAppender">
<appender-ref ref="FILE"/>
<queueSize>512</queueSize>
<discardingThreshold>0</discardingThreshold>
</appender>
<!-- Logger Configuration -->
<logger name="com.myapp" level="DEBUG"/>
<logger name="org.springframework" level="INFO"/>
<logger name="org.hibernate.SQL" level="DEBUG"/>
<root level="INFO">
<appender-ref ref="CONSOLE"/>
<appender-ref ref="ASYNC"/>
</root>
<!-- Profile-specific -->
<springProfile name="prod">
<root level="WARN">
<appender-ref ref="ASYNC"/>
</root>
</springProfile>
</configuration>
JSON Format (ELK Stack)
<appender name="JSON" class="ch.qos.logback.core.ConsoleAppender">
<encoder class="net.logstash.logback.encoder.LogstashEncoder">
<includeMdcKeyName>requestId</includeMdcKeyName>
<includeMdcKeyName>userId</includeMdcKeyName>
</encoder>
</appender>
MDC Usage
import org.slf4j.MDC;
MDC.put("requestId", UUID.randomUUID().toString());
MDC.put("userId", user.getId());
try {
// Business logic
} finally {
MDC.clear();
}
When NOT to Use This Skill
- SLF4J API questions: Focus on API usage, not Logback implementation details
- Log4j2 configuration: Different XML structure and features
- Application code logging: Use SLF4J API, Logback is just the implementation
- Non-Java projects: Use language-appropriate logging frameworks
- Simple console output: System.out may be sufficient for basic scripts
Anti-Patterns
| Anti-Pattern | Why It's Bad | Solution |
|---|---|---|
| Synchronous file appender in high-traffic | Blocks application threads | Use AsyncAppender wrapper |
| No rolling policy | Logs fill disk space | Use RollingFileAppender with size/time policies |
| Logging to console in production | Performance overhead, lost logs | Use file appenders, ship to centralized logging |
| DEBUG level in production | Performance impact, disk usage | Use INFO or WARN in production profiles |
| Not clearing MDC | Memory leaks, wrong context in threads | Always clear MDC in finally block |
| Hardcoded log paths | Breaks across environments | Use properties: ${LOG_PATH} |
Quick Troubleshooting
| Issue | Cause | Solution |
|---|---|---|
| Configuration not loaded | Wrong file name/location | Use logback-spring.xml in src/main/resources |
| Logs not rotating | Missing rolling policy | Add SizeAndTimeBasedRollingPolicy |
| Performance degradation | Synchronous appenders | Wrap with AsyncAppender |
| MDC values not appearing | Pattern missing MDC placeholders | Add %X{key} to pattern |
| Duplicate log entries | Logger additivity enabled | Set additivity="false" on logger |
| Profile-specific config ignored | Using logback.xml instead | Rename to logback-spring.xml for Spring profiles |