Getting absolute path of a file loaded via classpath

Use ClassLoader.getResource() instead of ClassLoader.getResourceAsStream() to get a URL. It will be, by definition, always absolute.

You can then use openConnection() on the URL to load the content. I’m often using this code:

public ... loadResource(String resource) {
    URL url = getClass().getClassLoader().getResource(resource);
    if (url == null) {
        throw new IllegalArgumentException("Unable to find " + resource + " on classpath);
    }

    log.debug("Loading {}", url); // Will print a file: or jar:file: URL with absolute path
    try(InputStream in = resource.openConnection()) {
        ...
    }
}