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Write specific logs to a log file spring-boot/slf4j

I am able to write console logs to rotating log files using this method here:
https://www.codejava.net/frameworks/spring-boot/logback-rolling-files-example
But my requirement is to write only specific logs to the log files instead of whole console log. For example, i need to write only the json messages(i can print them on console using log.info(message) which is supported by slf4j) being received by Kafka listener to the log files and nothing more. How can i achieve this in my spring-boot app? Is this not possible with slf4j logback?

Specify the appender-ref in your logger element.
So something like this in your logger XML configuration file:
<appender name="console" class="org.apache.log4j.ConsoleAppender">
<param name="Target" value="System.out"/>
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%-5p %c{1} - %m%n"/>
</layout>
</appender>
<appender name="bdfile" class="org.apache.log4j.RollingFileAppender">
<param name="append" value="false"/>
<param name="maxFileSize" value="1GB"/>
<param name="maxBackupIndex" value="2"/>
<param name="file" value="/tmp/bd.log"/>
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%-5p %c{1} - %m%n"/>
</layout>
</appender>
Then in the same config file, add a appender reference to the log file that you are interested in
<logger name="com.example.ClassWithJsonMessage" additivity="false">
<level value="debug"/>
<appender-ref ref="bdfile"/>
</logger>

log4j rolling appender issue for multiple log file creation

I am using log4j for my application for printing logs. Till now, I have only one log file(say X.log) and it is getting rolled after a fixed size, say, 4 MB. Now , I am trying to log some particular requests and responses to a different log file, Y. Log.
My requirement is to roll the Y.log file also, after 4 MB. I am using rolling file appender for both X and Y logs. Y.log will be created in the same location where X.log is available.
But it seems like now both the log files are not getting rolled over after 4 MB. It is keep on appending to the same logs and the size is increasing. Below is my log4j configuration.
<appender name="Xlogfile" class="org.apache.log4j.RollingFileAppender">
<param name="append" value="true" />
<param name="file" value="/logs/X.log" />
<param name="MaxBackupIndex" value="200" />
<param name="MaxFileSize" value="4MB" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d{dd MMM yyyy HH:mm:ss} %5p %c{1} - %m%n"/>
</layout>
</appender>
<appender name="Ylogfile" class="org.apache.log4j.RollingFileAppender">
<param name="append" value="true" />
<param name="file" value="/logs/Y.log" />
<param name="MaxBackupIndex" value="200" />
<param name="MaxFileSize" value="4MB" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d{dd MMM yyyy HH:mm:ss} %5p %c{1} - %m%n"/>
</layout>
</appender>
<root>
<level value="INFO" />
<appender-ref ref=" Xlogfile " />
<appender-ref ref=" Ylogfile " />
</root>
Could anyone please provide me a solution for this. Thanks in advance.

Try adding a policy to your appender, like this:
<Policies>
<SizeBasedTriggeringPolicy size="4mb"/>
</Policies>

Logging different levels using same object to different files

My simple question is : If I have two statements like logger.info() and logger.error() in Java (using log4j), I want the results of these two lines to be printed in two separate files. That is, logger.info(...) should print to a file say myLog.info and logger.error(...) should print to myLog.error file. I am using rolling file appender for this task. Also I want just one logger object to do the task. Someone might suggest two or more different loggers one for each file, but that's not the case.
I tried searching a solution for the problem. One of the links Creating multiple log files of different content with log4j says about "threshold" and I even tried to add threshold in my xml configuration file. But what it actually is doing that : info log is being printed in myLog.info file but error log gets printed in both the files. Can it be done through xml configuration file alone or a separate properties file is needed? If xml file is sufficient, then what needs to be done?
I am preferring xml file over properties file. If there is a working solution using only xml configuration file, that would be sufficient. Thanks in advance.

You could use filters to deny any messages except those of the level you want. Here is an example of how to do this:
First a class to test our efforts:
package test;
import org.apache.log4j.Logger;
public class Main {
private static final Logger logger = Logger.getLogger(Main.class);
public static void main(String[] args) {
logger.debug("here's some debug");
logger.info("here's some info");
logger.warn("here's some warn");
logger.error("here's some error");
logger.fatal("here's some fatal");
}
}
Next a log4j.xml config file to set up the appenders and loggers:
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j='http://jakarta.apache.org/log4j/'>
<appender name="consoleAppender" class="org.apache.log4j.ConsoleAppender">
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d %-5p [%c{1}] %m %n" />
</layout>
</appender>
<appender name="debugLog" class="org.apache.log4j.RollingFileAppender">
<param name="File" value="logs/debug.log" />
<param name="Append" value="true" />
<param name="MaxFileSize" value="5000KB" />
<param name="maxBackupIndex" value="5" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d{yyyy-MM-dd HH:mm:ss} [%t] %-5p - %m%n" />
</layout>
<filter class="org.apache.log4j.varia.LevelMatchFilter">
<param name="LevelToMatch" value="DEBUG" />
<param name="AcceptOnMatch" value="true" />
</filter>
<filter class="org.apache.log4j.varia.DenyAllFilter" />
</appender>
<appender name="infoLog" class="org.apache.log4j.RollingFileAppender">
<param name="File" value="logs/info.log" />
<param name="Append" value="true" />
<param name="MaxFileSize" value="5000KB" />
<param name="maxBackupIndex" value="5" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d{yyyy-MM-dd HH:mm:ss} [%t] %-5p - %m%n" />
</layout>
<filter class="org.apache.log4j.varia.LevelMatchFilter">
<param name="LevelToMatch" value="INFO" />
<param name="AcceptOnMatch" value="true" />
</filter>
<filter class="org.apache.log4j.varia.DenyAllFilter" />
</appender>
<logger name="test" additivity="false">
<level value="DEBUG" />
<appender-ref ref="consoleAppender" />
<appender-ref ref="debugLog" />
<appender-ref ref="infoLog" />
</logger>
</log4j:configuration>
This pattern will allow you to generate a separate log for each log level, just repeat the configuration that I have provided for either debug or info logging. Note that the console appender will accept all levels.
I was able to gain some insight from this post so I thought I should give credit.

How to use syslog with LOG4J 1.x?

I want to config my LOG4J. I can't update the version to 2.x because it's a big application. The actual Documentation for the LOG4J version 1.x is offline.
Here is my actual config for the appender:
<appender name="syslog" class="org.apache.log4j.net.SyslogAppender">
<param name="SyslogHost" value="localhost:514"/>
<param name="Facility" value="LOCAL1"/>
<param name="FacilityPrinting" value="true"/>
<param name="Threshold" value="WARN"/>
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d{dd.MMM.yyyy HH:mm:ss} %-5p %m%n"/>
</layout>
</appender>
I tested it with : netstat -a -b > test.txt
But i dont't found something with the Port 514.
Can somebody help me(because he made experience with LOG4J 1.x), or has somebody a copy of the documentation from LOG4J 1.x ?

<appender name="Syslog" class="org.apache.log4j.net.SyslogAppender">
<param name="SyslogHost" value="IP:514"/>
<param name="Facility" value="USER"/>
<param name="FacilityPrinting" value="true"/>
<param name="Threshold" value="INFO"/>
<layout class="org.apache.log4j.IvyLog4jLayout">
<param name="DateFormat" value="MM/dd/yyyy hh:mm:ss"/>
</layout>
</appender>
This way it worked for me :)

log4j writing to rolled over file

We have set log4j rollover as 500mb upon 500 mb it is creating a file new file log.1 but still it is sometimes writing to log.1 and to log and sometimes only to log and some times to log.1.
I am using apache tomcat.
It is so inconsistent.
<!-- Appenders -->
<appender name="console" class="org.apache.log4j.ConsoleAppender">
<param name="Target" value="System.out" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d %-5p: %c - %m%n" />
</layout>
</appender>
<appender name="file" class="org.apache.log4j.RollingFileAppender">
<param name="maxFileSize" value="500MB" />
<param name="maxBackupIndex" value="5" />
<param name="Append" value="true"/>
<param name="File" value="c:/logs/web.log" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d %p [%c] - %m%n" />
</layout>
</appender>
Could you please let me know any reason for this?
Regards,
Adam