Simulation class could not be loaded

[Prachi_Gupta]

Gatling version: 3.9.5 (must be up to date)
Gatling flavor: java kotlin scala javascript typescript
Gatling build tool: maven gradle sbt bundle npm

I read the guidelines and how to ask a question topics.
I provided a SSCCE (or at least, all information to help the community understand my topic)
I copied output I observe, and explain what I think should be.

I am trying to build kafka load testing and run the application via main class. To remove the dependency on gradlew i am using gatling api. By giving command ./gradlew gatlingRun it is able to run but not via main class.

It is not able to load simulation class.

This is my build.gradle->

dependencies {
    implementation 'io.gatling:gatling-core:3.9.5'
    implementation 'io.gatling:gatling-app:3.9.5'
    implementation 'io.gatling.highcharts:gatling-charts-highcharts:3.9.5'
    implementation 'org.scala-lang:scala-library:2.13.14'
    gatling 'org.galaxio:gatling-kafka-plugin_2.13:0.12.0'
}

gatling {
}

sourceSets {
    gatling {
        java {
            srcDir 'src/gatling/java'
        }
    }
}

Service class

import io.gatling.app.Gatling;
import io.gatling.core.config.GatlingPropertiesBuilder;

public class GatlingService {
    public void runKafkaSimulation() {

        GatlingPropertiesBuilder props = new GatlingPropertiesBuilder();
        props.simulationClass("com.project.loadtesting.KafkaSimulation");

        try {
            Gatling.fromMap(props.build());
        } catch (Exception e) {
            System.err.println("Failed to run Gatling simulation: " + e.getMessage());
            e.printStackTrace();
        }
    }
}

Error:
22:00:34.950 [main] ERROR io.gatling.app.Gatling$ -- Run crashed
java.lang.IllegalArgumentException: User defined Simulation class com.finance.project.loadtesting.KafkaSimulation could not be loaded
	at io.gatling.app.Selection$Selector.findUserDefinedSimulationInClassloader$1(Selection.scala:84)

[slandelle]

I am trying to … run the application via main class.

This is not a supported usage. Please stick to the official launchers: maven, gradle and sbt instead of trying to hack our internals.