Logback to log different messages to two files

java

logback

logging

configuration

byAnton Shumikhin·Aug 28, 2024

In Logback, to log different messages to two files, you'll define a pair of appenders and loggers within your logback.xml file. Each appender aligns with a targeted output file. By mapping specific logs from each class to their respective appender, you can effectively split the logs. Here's a handy example:

<configuration>
  
  <appender name="FILE_1" class="ch.qos.logback.core.FileAppender">
    <file>first.log</file>
    <encoder>
      <pattern>%msg%n</pattern>
    </encoder>
  </appender>
  
  <appender name="FILE_2" class="ch.qos.logback.core.FileAppender">
    <file>second.log</file>
    <encoder>
      <pattern>%msg%n</pattern>
    </encoder>
  </appender>

  <logger name="com.app.First" level="info">
    <appender-ref ref="FILE_1" />
  </logger>

  <logger name="com.app.Second" level="info">
    <appender-ref ref="FILE_2" />
  </logger>

</configuration>

Here, logs emitted from com.app.First neatly land into first.log, while com.app.Second directs its logs to second.log. Replace com.app with your package name.

Combat log duplication with non-additive loggers

Nobody likes duplicating things, especially not logs! Ensure your logs don’t cascade to the root logger by setting additivity=false.

<logger name="com.app.First" additivity="false"> <!-- No more copy-pasting those logs! -->
  <appender-ref ref="FILE_1" />
</logger>

Dealing with mega logs using RollingFileAppender

When your logs start bloating up, it's time to call in our friend, RollingFileAppender. Acting as a virtual waste management system, this guy helps to handle and manage large file sizes.

Log levels - Your personal verbosity controller

Set unique log levels for each logger. It’s like having a volume controller on a stereo, controlling how much log noise you want emitted.

<logger name="com.app.debug" level="debug"> <!-- Unleash the chatter! -->
  ...
</logger>
<logger name="com.app.error" level="error"> <!-- Only the critical stuff, please. -->
  ...
</logger>

Customizing with encoded patterns

Dress your logs to impress. Using encoder, add timestamps, log levels, and class names to give your logs the detailing they deserve:

<encoder>
  <pattern>%d{"HH:mm:ss.SSS"} [%thread] %-5level %logger{36} - %msg%n</pattern> <!-- Dress them up fancy! -->
</encoder>

Cluster related classes under the same package and let them share a logger. Improves maintainability and keeps things organized.

Logging with surgical precision

Take control with <appender-ref>. Send logs to their intended destination right at their birthplace.

Logger names – They mean something!

Naming loggers after their class or functionality can help in understanding from where and why the logs were generated.

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Combat log duplication with non-additive loggers Dealing with mega logs using RollingFileAppender Log levels - Your personal verbosity controller Customizing with encoded patterns Sharing loggers - The secret to order and consistency Logging with surgical precision Logger names – They mean something!