In Logback, it is easy to set a log file name programmatically :
- In
logback.xml, declares a variable like${log.name} - In Java, set the variable via
System.setProperty("log.name", "abc")
1. Full example
1.1 A logback file, we will set the ${log.name} variable later.
src/main/resources/logback.xml
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<property name="PRO_HOME" value="/home/mkyong/ant/logs" />
<property name="USER_HOME" value="${PRO_HOME}" />
<timestamp key="bySecond" datePattern="yyyyMMdd.HHmmss" />
<appender name="FILE-ENGINE-ERROR" class="ch.qos.logback.core.FileAppender">
<file>${USER_HOME}/${log.name}.error</file>
<encoder>
<pattern>%d{yyyy-MM-dd HH:mm:ss} [%thread] %-5level %logger{36} - %msg%n</pattern>
</encoder>
</appender>
<appender name="FILE-ENGINE" class="ch.qos.logback.core.FileAppender">
<file>${USER_HOME}/${log.name}-${bySecond}.log</file>
<encoder>
<pattern>%d{yyyy-MM-dd HH:mm:ss} [%thread] %-5level %logger{35} - %msg%n</pattern>
</encoder>
</appender>
<logger name="com.mkyong.core" level="debug" additivity="false">
<appender-ref ref="FILE-ENGINE" />
</logger>
<logger name="org.springframework" level="error" additivity="false">
<appender-ref ref="FILE-ENGINE-ERROR" />
</logger>
<root level="error">
<appender-ref ref="FILE-ENGINE-ERROR" />
</root>
</configuration>
1.2 In Java, just set the file name via System.setProperty
AntRunApp.java
package com.mkyong.core;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class AntRunApp {
private final Logger logger = LoggerFactory.getLogger(AntRunApp.class);
public static void main(String[] args) {
//Set this before the logger start.
System.setProperty("log.name", "mkyong");
AntRunApp obj = new AntRunApp();
obj.start();
}
private void start() {
logger.debug("------ Starting Ant------");
//...
}
}
Output
Debug log file path /home/mkyong/ant/logs/mkyong-20150323.221959.log Error log file path /home/mkyong/ant/logs/mkyong.error
2. log.name.rir_IS_UNDEFINED.log
2.1 A common error, normally it is caused by the static logger. For example.
AntRunApp.java
package com.mkyong.core;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class AntRunApp {
// static, this logger will be initialized before the program is run.
// All logs will be redirected to log.name.rir_IS_UNDEFINED.log
private static final Logger logger = LoggerFactory.getLogger(AntRunApp.class);
private void start() {
System.setProperty("log.name", "mkyong");
logger.debug("------ Starting Ant------");
//...
}
}
To fix it, just delete the static type.
2.2 If you logs before the System.setProperty, this will also cause the common Logback variable UNDEFINED error.
AntRunApp.java
package com.mkyong.core;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class AntRunApp {
private final Logger logger = LoggerFactory.getLogger(AntRunApp.class);
private void start() {
//Please set the log name first!
logger.debug("------ Starting Ant------");
System.setProperty("log.name", "mkyong");
}
}
Very useful, and to the point. This worked for me, thanks! 🙂
trying to pass a variable like this
app.${bySecond}.log
<timestamp key=”bySecond” datePattern=”yyyy-MM-dd’T’HH:mm:ss.SSSZZ”/>
Getting error
at java.io.FileNotFoundException: logs\app.2020-08-20T14:52:43.911-0500.log (The filename, directory name, or volume label syntax is incorrect)
Hello,
I am trying to implement your method but it’s now working for me, and I was wondering if that would be because I have log4j.properties instead of .xml? My code seems to replace the variable I created with an empty string.
Here is the content of my file
log4j.rootLogger=TRACE, STDOUT, file
log4j.appender.STDOUT=org.apache.log4j.ConsoleAppender
log4j.appender.STDOUT.layout=org.apache.log4j.PatternLayout
log4j.appender.STDOUT.layout.ConversionPattern=%c{1} – %m%n
log4j.appender.STDOUT.Threshold=INFO
log4j.appender.file=org.apache.log4j.DailyRollingFileAppender
log4j.appender.file.File=${basedir}/${log.file}.log
log4j.appender.file.DatePattern=’-‘yyyy-MM-dd-HH’.log’
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%-5p %d{yyyy-MM-dd HH:mm:ss} %C:%L – %m%n
if it’s happened in the Servlet Container (tomcat, jboss), using log4j2 usually it need to reconfigure the logger using LoggerContext.
What will happen if we’re doing that using Logback?