Chapter 4: Logback Configuration
Introduction
Logback is the default logging implementation for Spring Boot. This chapter teaches you how to configure it for different environments.
🎯 Chapter Objectives
By the end of this chapter, you will know how to:
- ✅ Create a logback-spring.xml file
- ✅ Configure appenders (Console, File, Rolling)
- ✅ Customize log patterns
- ✅ Use Spring profiles
- ✅ Configure JSON logs for production
1. Basic Configuration
logback-spring.xml File
Create src/main/resources/logback-spring.xml:
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<!-- Import Spring Boot values -->
<include resource="org/springframework/boot/logging/logback/defaults.xml"/>
<!-- Variable for application name -->
<springProperty scope="context" name="APP_NAME" source="spring.application.name" defaultValue="myapp"/>
<!-- Console Appender -->
<appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
<encoder>
<pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
</encoder>
</appender>
<!-- Default configuration -->
<root level="INFO">
<appender-ref ref="CONSOLE"/>
</root>
<!-- Specific level for your application -->
<logger name="com.myapp" level="DEBUG"/>
</configuration>
2. Log Patterns
Pattern Syntax
| Pattern | Description | Example |
|---|---|---|
%d\{format\} | Date/time | 2024-01-15 10:30:00 |
%thread | Thread name | http-nio-8080-exec-1 |
%level / %-5level | Level (padded) | INFO |
%logger\{n\} | Logger name (n chars) | c.m.s.UserService |
%msg | Message | User logged in |
%n | New line | |
%X\{key\} | MDC value | abc-123 |
%highlight() | Colors (console) |
Pattern Examples
<!-- Simple -->
<pattern>%d{HH:mm:ss} %-5level %logger{36} - %msg%n</pattern>
<!-- Output: 10:30:00 INFO c.m.s.UserService - User logged in -->
<!-- With MDC -->
<pattern>%d{HH:mm:ss} [%X{requestId}] [%X{userId}] %-5level %logger{36} - %msg%n</pattern>
<!-- Output: 10:30:00 [abc-123] [42] INFO c.m.s.UserService - User logged in -->
<!-- Colored for console -->
<pattern>%d{HH:mm:ss} %highlight(%-5level) %cyan(%logger{36}) - %msg%n</pattern>
<!-- Detailed for file -->
<pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] [%X{requestId:-N/A}] %-5level %logger{50} - %msg%n</pattern>
3. Appenders
Console Appender
<appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
<encoder>
<pattern>%d{HH:mm:ss.SSS} %highlight(%-5level) %cyan(%logger{36}) - %msg%n</pattern>
</encoder>
</appender>
File Appender (simple file)
<appender name="FILE" class="ch.qos.logback.core.FileAppender">
<file>logs/application.log</file>
<append>true</append>
<encoder>
<pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{50} - %msg%n</pattern>
</encoder>
</appender>
Rolling File Appender (with rotation)
<appender name="ROLLING_FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
<file>logs/application.log</file>
<!-- Rotation policy -->
<rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
<!-- Archived file names -->
<fileNamePattern>logs/application.%d{yyyy-MM-dd}.%i.log.gz</fileNamePattern>
<!-- Max size per file -->
<maxFileSize>10MB</maxFileSize>
<!-- Retention days -->
<maxHistory>30</maxHistory>
<!-- Total max size -->
<totalSizeCap>1GB</totalSizeCap>
</rollingPolicy>
<encoder>
<pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] [%X{requestId}] %-5level %logger{50} - %msg%n</pattern>
</encoder>
</appender>
4. Spring Profiles
Profile-Based Configuration
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<include resource="org/springframework/boot/logging/logback/defaults.xml"/>
<!-- Console Appender (always present) -->
<appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
<encoder>
<pattern>%d{HH:mm:ss.SSS} %highlight(%-5level) %cyan(%logger{36}) - %msg%n</pattern>
</encoder>
</appender>
<!-- ===== DEV PROFILE ===== -->
<springProfile name="dev">
<root level="INFO">
<appender-ref ref="CONSOLE"/>
</root>
<logger name="com.myapp" level="DEBUG"/>
<logger name="org.hibernate.SQL" level="DEBUG"/>
</springProfile>
<!-- ===== PROD PROFILE ===== -->
<springProfile name="prod">
<!-- File with rotation -->
<appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
<file>/var/log/myapp/application.log</file>
<rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
<fileNamePattern>/var/log/myapp/application.%d{yyyy-MM-dd}.%i.log.gz</fileNamePattern>
<maxFileSize>50MB</maxFileSize>
<maxHistory>30</maxHistory>
<totalSizeCap>5GB</totalSizeCap>
</rollingPolicy>
<encoder>
<pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] [%X{requestId}] %-5level %logger{50} - %msg%n</pattern>
</encoder>
</appender>
<root level="WARN">
<appender-ref ref="FILE"/>
</root>
<logger name="com.myapp" level="INFO"/>
</springProfile>
<!-- ===== TEST PROFILE ===== -->
<springProfile name="test">
<root level="WARN">
<appender-ref ref="CONSOLE"/>
</root>
<logger name="com.myapp" level="INFO"/>
</springProfile>
</configuration>
5. JSON Logs for Production
Why JSON?
Text logs:
2024-01-15 10:30:00 INFO UserService - User 42 logged in
JSON logs (parsable by ELK, Datadog, etc.):
{"timestamp":"2024-01-15T10:30:00.000Z","level":"INFO","logger":"UserService","message":"User logged in","userId":42}
Dependency
<dependency>
<groupId>net.logstash.logback</groupId>
<artifactId>logstash-logback-encoder</artifactId>
<version>7.4</version>
</dependency>
JSON Configuration
<!-- JSON Appender -->
<appender name="JSON_FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
<file>/var/log/myapp/application.json</file>
<rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
<fileNamePattern>/var/log/myapp/application.%d{yyyy-MM-dd}.%i.json.gz</fileNamePattern>
<maxFileSize>50MB</maxFileSize>
<maxHistory>7</maxHistory>
</rollingPolicy>
<!-- JSON Encoder -->
<encoder class="net.logstash.logback.encoder.LogstashEncoder">
<includeMdcKeyName>requestId</includeMdcKeyName>
<includeMdcKeyName>userId</includeMdcKeyName>
<customFields>{"app":"myapp","env":"prod"}</customFields>
</encoder>
</appender>
<springProfile name="prod">
<root level="INFO">
<appender-ref ref="JSON_FILE"/>
</root>
</springProfile>
JSON Output
{
"@timestamp": "2024-01-15T10:30:00.000Z",
"@version": "1",
"message": "User logged in",
"logger_name": "com.myapp.service.UserService",
"thread_name": "http-nio-8080-exec-1",
"level": "INFO",
"requestId": "abc-123",
"userId": "42",
"app": "myapp",
"env": "prod"
}
6. Professional Complete Configuration
<?xml version="1.0" encoding="UTF-8"?>
<configuration scan="true" scanPeriod="30 seconds">
<include resource="org/springframework/boot/logging/logback/defaults.xml"/>
<springProperty scope="context" name="APP_NAME" source="spring.application.name" defaultValue="myapp"/>
<property name="LOG_PATH" value="${LOG_PATH:-logs}"/>
<!-- ===== CONSOLE APPENDER ===== -->
<appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
<encoder>
<pattern>%d{HH:mm:ss.SSS} [%X{requestId:-}] %highlight(%-5level) %cyan(%logger{36}) - %msg%n</pattern>
</encoder>
</appender>
<!-- ===== FILE APPENDER (Text) ===== -->
<appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
<file>${LOG_PATH}/${APP_NAME}.log</file>
<rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
<fileNamePattern>${LOG_PATH}/archived/${APP_NAME}.%d{yyyy-MM-dd}.%i.log.gz</fileNamePattern>
<maxFileSize>50MB</maxFileSize>
<maxHistory>30</maxHistory>
<totalSizeCap>5GB</totalSizeCap>
</rollingPolicy>
<encoder>
<pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] [%X{requestId:-N/A}] [%X{userId:-anonymous}] %-5level %logger{50} - %msg%n</pattern>
</encoder>
</appender>
<!-- ===== ERROR FILE APPENDER ===== -->
<appender name="ERROR_FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
<file>${LOG_PATH}/${APP_NAME}-error.log</file>
<filter class="ch.qos.logback.classic.filter.ThresholdFilter">
<level>ERROR</level>
</filter>
<rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
<fileNamePattern>${LOG_PATH}/archived/${APP_NAME}-error.%d{yyyy-MM-dd}.%i.log.gz</fileNamePattern>
<maxFileSize>50MB</maxFileSize>
<maxHistory>90</maxHistory>
</rollingPolicy>
<encoder>
<pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] [%X{requestId}] %-5level %logger{50} - %msg%n%ex</pattern>
</encoder>
</appender>
<!-- ===== ASYNC APPENDER (Performance) ===== -->
<appender name="ASYNC_FILE" class="ch.qos.logback.classic.AsyncAppender">
<queueSize>512</queueSize>
<discardingThreshold>0</discardingThreshold>
<includeCallerData>false</includeCallerData>
<appender-ref ref="FILE"/>
</appender>
<!-- ===== DEV PROFILE ===== -->
<springProfile name="dev,local">
<root level="INFO">
<appender-ref ref="CONSOLE"/>
</root>
<logger name="com.myapp" level="DEBUG"/>
<logger name="org.hibernate.SQL" level="DEBUG"/>
<logger name="org.springframework.web" level="DEBUG"/>
</springProfile>
<!-- ===== PROD PROFILE ===== -->
<springProfile name="prod">
<root level="WARN">
<appender-ref ref="ASYNC_FILE"/>
<appender-ref ref="ERROR_FILE"/>
</root>
<logger name="com.myapp" level="INFO"/>
</springProfile>
<!-- ===== TEST PROFILE ===== -->
<springProfile name="test">
<root level="WARN">
<appender-ref ref="CONSOLE"/>
</root>
<logger name="com.myapp" level="INFO"/>
</springProfile>
<!-- ===== DEFAULT (no profile) ===== -->
<springProfile name="default">
<root level="INFO">
<appender-ref ref="CONSOLE"/>
<appender-ref ref="FILE"/>
</root>
<logger name="com.myapp" level="DEBUG"/>
</springProfile>
</configuration>
7. Useful Specific Loggers
<!-- Hibernate SQL Queries -->
<logger name="org.hibernate.SQL" level="DEBUG"/>
<logger name="org.hibernate.type.descriptor.sql.BasicBinder" level="TRACE"/>
<!-- Spring Security -->
<logger name="org.springframework.security" level="DEBUG"/>
<!-- Incoming HTTP Requests -->
<logger name="org.springframework.web.filter.CommonsRequestLoggingFilter" level="DEBUG"/>
<!-- Connection Pool -->
<logger name="com.zaxxer.hikari" level="DEBUG"/>
<!-- Transactions -->
<logger name="org.springframework.transaction" level="DEBUG"/>
<!-- Disable noisy logs -->
<logger name="org.apache.catalina" level="WARN"/>
<logger name="org.apache.tomcat" level="WARN"/>
8. Summary
Configuration Files
| File | Usage |
|---|---|
application.properties | Simple config |
logback-spring.xml | Advanced config |
logback.xml | Config without Spring |
Common Appenders
| Appender | Usage |
|---|---|
ConsoleAppender | Console (dev) |
FileAppender | Simple file |
RollingFileAppender | File with rotation |
AsyncAppender | Performance (prod) |
Recommended Pattern
%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] [%X{requestId}] %-5level %logger{50} - %msg%n
🎯 Next Step
Time for practice! Let's implement a complete error handling and logging system.
➡️ TP10.1: Centralized Error Management