Read properties file outside JAR file

So, you want to treat your .properties file on the same folder as the main/runnable jar as a file rather than as a resource of the main/runnable jar. In that case, my own solution is as follows:

First thing first: your program file architecture shall be like this (assuming your main program is main.jar and its main properties file is main.properties):

./ - the root of your program
 |__ main.jar
 |__ main.properties

With this architecture, you can modify any property in the main.properties file using any text editor before or while your main.jar is running (depending on the current state of the program) since it is just a text-based file. For example, your main.properties file may contain:

app.version=1.0.0.0
app.name=Hello

So, when you run your main program from its root/base folder, normally you will run it like this:

java -jar ./main.jar

or, straight away:

java -jar main.jar

In your main.jar, you need to create a few utility methods for every property found in your main.properties file; let say the app.version property will have getAppVersion() method as follows:

/**
 * Gets the app.version property value from
 * the ./main.properties file of the base folder
 *
 * @return app.version string
 * @throws IOException
 */

import java.util.Properties;

public static String getAppVersion() throws IOException{

    String versionString = null;

    //to load application's properties, we use this class
    Properties mainProperties = new Properties();

    FileInputStream file;

    //the base folder is ./, the root of the main.properties file  
    String path = "./main.properties";

    //load the file handle for main.properties
    file = new FileInputStream(path);

    //load all the properties from this file
    mainProperties.load(file);

    //we have loaded the properties, so close the file handle
    file.close();

    //retrieve the property we are intrested, the app.version
    versionString = mainProperties.getProperty("app.version");

    return versionString;
}

In any part of the main program that needs the app.version value, we call its method as follows:

String version = null;
try{
     version = getAppVersion();
}
catch (IOException ioe){
    ioe.printStackTrace();
}