Run jar with external properties file

I have a jar with a main class that can be executed as: java -jar test.jar

Inside the jar there is something like

public static void main(String[] args) throws IOException {
    InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream("config.properties");
    Properties prop = new Properties();
    prop.load(is);
    //then I wanna fetch all the properties in the config.properties file
}

I run both:

• java -jar test.jar

• java -jar test.jar -cp / tmp (where config.properties is located)

• java -jar test.jar -cp / tmp / config.properties (obviously it doesn't work, but it gives you an idea of ​​what I'm trying to achieve here)

The code does not work, all three throw NPE, although I put the path of the config.properties file under my $ PATH and $ CLASSPATH.

The fact is that in the end I will put the configuration file in $ {my-config-path} and read / process it correctly. But temporarily, I just want something fast and dirty.

• I DO NOT want to include the properties file in my jar.
• I want to save it from the outside in the way to classes or the way, when I execute the jar, it finds it without problems.