I have been working on a java object that needs some logging facility. I implemented this with org.slf4j.simple.SimpleLogger. Here is a test:
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class Main {
static Logger log = LoggerFactory.getLogger(Main.class);
public static void main(String[] args) {
String message;
if (args.length == 0) {
message = "Hello world";
} else {
message = args[0];
}
new Main(message);
}

public Main(String message) {
System.out.println(LoggerFactory.class.getResource("LoggerFactory.class"));
log.info(message);
}
}
If I call Main(), it works and reports
$ java -jar target/logtest-1.0.jar
jar:file:/home/jeffemandel/logtest/target/logtest-1.0.jar!/org/slf4j/LoggerFactory.class
2025-11-09 11:12:55.494 [INFO] org.jeffmandel.logtest.Main – Hello world
From MATLAB, calling Main reports
>> Main(‘test’);
jar:file:/Applications/MATLAB_R2025b.app/java/jarext/slf4j/slf4j-api.jar!/org/slf4j/LoggerFactory.class
Since I don’t have log4j12 configured, the output goes to NOP.
As noted in this Stackoverflow answer, if I add the full path to slf4j-api-2.0.17.jar to my javaclasspath.txt with the tag <before>, I get the expected behavior:
>> Main(‘Hello world’);
jar:file:/Users/jeffemandel/.m2/repository/org/slf4j/slf4j-api/2.0.17/slf4j-api-2.0.17.jar!/org/slf4j/LoggerFactory.class
2025-11-09 11:24:47.349 [INFO] org.jeffmandel.logtest.Main – Hello world
Finally, if I add logtest-1.0.jar with the <before> tag, I don’t need to add slf4j-api-2.0.17.jar to javaclasspath.txt
>> Main(‘Hello world’);
jar:file:/Users/jeffemandel/MATLAB-Drive/dise_service/logtest-1.0.jar!/org/slf4j/LoggerFactory.class
2025-11-09 11:26:44.041 [INFO] org.jeffmandel.logtest.Main – Hello world
This seems to be the best approach, as it avoids cluttering up the classpath with jars I only need in my own objects.
Now I get that this is a long run for a short slide (I could just configure my object to use slf4j-log4j12), but according to the author of the SO post this undocumented feature has been around since 2013a, so maybe it should be a standard feature. I say this because on the way to understanding the issue, I saw the recommendation to edit the file that says don’t edit this file, and saw someone who solved the problem by deleting slf4j-api.jar from jarext.I have been working on a java object that needs some logging facility. I implemented this with org.slf4j.simple.SimpleLogger. Here is a test:
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class Main {
static Logger log = LoggerFactory.getLogger(Main.class);
public static void main(String[] args) {
String message;
if (args.length == 0) {
message = "Hello world";
} else {
message = args[0];
}
new Main(message);
}

public Main(String message) {
System.out.println(LoggerFactory.class.getResource("LoggerFactory.class"));
log.info(message);
}
}
If I call Main(), it works and reports
$ java -jar target/logtest-1.0.jar
jar:file:/home/jeffemandel/logtest/target/logtest-1.0.jar!/org/slf4j/LoggerFactory.class
2025-11-09 11:12:55.494 [INFO] org.jeffmandel.logtest.Main – Hello world
From MATLAB, calling Main reports
>> Main(‘test’);
jar:file:/Applications/MATLAB_R2025b.app/java/jarext/slf4j/slf4j-api.jar!/org/slf4j/LoggerFactory.class
Since I don’t have log4j12 configured, the output goes to NOP.
As noted in this Stackoverflow answer, if I add the full path to slf4j-api-2.0.17.jar to my javaclasspath.txt with the tag <before>, I get the expected behavior:
>> Main(‘Hello world’);
jar:file:/Users/jeffemandel/.m2/repository/org/slf4j/slf4j-api/2.0.17/slf4j-api-2.0.17.jar!/org/slf4j/LoggerFactory.class
2025-11-09 11:24:47.349 [INFO] org.jeffmandel.logtest.Main – Hello world
Finally, if I add logtest-1.0.jar with the <before> tag, I don’t need to add slf4j-api-2.0.17.jar to javaclasspath.txt
>> Main(‘Hello world’);
jar:file:/Users/jeffemandel/MATLAB-Drive/dise_service/logtest-1.0.jar!/org/slf4j/LoggerFactory.class
2025-11-09 11:26:44.041 [INFO] org.jeffmandel.logtest.Main – Hello world
This seems to be the best approach, as it avoids cluttering up the classpath with jars I only need in my own objects.
Now I get that this is a long run for a short slide (I could just configure my object to use slf4j-log4j12), but according to the author of the SO post this undocumented feature has been around since 2013a, so maybe it should be a standard feature. I say this because on the way to understanding the issue, I saw the recommendation to edit the file that says don’t edit this file, and saw someone who solved the problem by deleting slf4j-api.jar from jarext. I have been working on a java object that needs some logging facility. I implemented this with org.slf4j.simple.SimpleLogger. Here is a test:
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class Main {
static Logger log = LoggerFactory.getLogger(Main.class);
public static void main(String[] args) {
String message;
if (args.length == 0) {
message = "Hello world";
} else {
message = args[0];
}
new Main(message);
}

public Main(String message) {
System.out.println(LoggerFactory.class.getResource("LoggerFactory.class"));
log.info(message);
}
}
If I call Main(), it works and reports
$ java -jar target/logtest-1.0.jar
jar:file:/home/jeffemandel/logtest/target/logtest-1.0.jar!/org/slf4j/LoggerFactory.class
2025-11-09 11:12:55.494 [INFO] org.jeffmandel.logtest.Main – Hello world
From MATLAB, calling Main reports
>> Main(‘test’);
jar:file:/Applications/MATLAB_R2025b.app/java/jarext/slf4j/slf4j-api.jar!/org/slf4j/LoggerFactory.class
Since I don’t have log4j12 configured, the output goes to NOP.
As noted in this Stackoverflow answer, if I add the full path to slf4j-api-2.0.17.jar to my javaclasspath.txt with the tag <before>, I get the expected behavior:
>> Main(‘Hello world’);
jar:file:/Users/jeffemandel/.m2/repository/org/slf4j/slf4j-api/2.0.17/slf4j-api-2.0.17.jar!/org/slf4j/LoggerFactory.class
2025-11-09 11:24:47.349 [INFO] org.jeffmandel.logtest.Main – Hello world
Finally, if I add logtest-1.0.jar with the <before> tag, I don’t need to add slf4j-api-2.0.17.jar to javaclasspath.txt
>> Main(‘Hello world’);
jar:file:/Users/jeffemandel/MATLAB-Drive/dise_service/logtest-1.0.jar!/org/slf4j/LoggerFactory.class
2025-11-09 11:26:44.041 [INFO] org.jeffmandel.logtest.Main – Hello world
This seems to be the best approach, as it avoids cluttering up the classpath with jars I only need in my own objects.
Now I get that this is a long run for a short slide (I could just configure my object to use slf4j-log4j12), but according to the author of the SO post this undocumented feature has been around since 2013a, so maybe it should be a standard feature. I say this because on the way to understanding the issue, I saw the recommendation to edit the file that says don’t edit this file, and saw someone who solved the problem by deleting slf4j-api.jar from jarext. matlab, java, slf4j MATLAB Answers — New Questions

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