Placing java classes at the head of javaclasspath

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.

Answer 1

[Leepakshi]

Hi Jeff,

The solution you can try is to add your own SLF4J JAR (and backend) to MATLAB’s javaclasspath.txt with the <before> tag, ensuring your version is used and logging works as expected.

Thanks