Load resource from anywhere in classpath

Question

I have a simple java application that loads a properties file from the current package.

this.getClass().getResourceAsStream("props.properties");

This works fine when the property file I want is in the current package. However, I want to package this application as a JAR and define and override with a new properties file where I use it. Is there a way to load the first resource named "props.properties" that is on the classpath?

I want it to be as easy to override the properties file via command line:

java.exe -classpath props.properties;myJar.jar com.test.MyApp

I don't want to have to unpack the JAR and modify the properties file to change something. I feel like I'm missing something obvious...

Answer 1

The javadoc for Class.getResourceAsStream() documents the lookup logic:

If the name begins with a '/' ('\u002f'), then the absolute name of the resource is the portion of the name following the '/'.

Otherwise, the absolute name is of the following form:
modified_package_name/name

Where the modified_package_name is the package name of this object with '/' substituted for '.' ('\u002e').

So in other words, the resource name passed to the method should look like /com/package/p2/props.properties if the props.properties is stored in the com.package.p2 package instead of the current class's.

Answer 2

I'm sure it's too late for the answer but it could be interesting for googlers this small code snippet helpers to load a properties file from any where in the Classpath.

ClassLoader cl = ClassLoader.getSystemClassLoader();
    if (cl != null) {
        URL url = cl.getResource(CONF_PROPERTIES);
        if (url == null) {
            url = cl.getResource("/" + CONF_PROPERTIES);
        }
        if (url != null) {
            try {
                InputStream in = url.openStream();
                props = new Properties();
                props.load(in);
            } catch (IOException e) {
                // Log the exception
            } finally {
               // close opened resources
            }

        }
    }