ninja-core/src/main/java/ninja/AssetsControllerHelper.java
public boolean isDirectoryURL(URL url) {
        try {
            return url.getProtocol().equals("file") && new File(url.toURI()).isDirectory();
        } catch (URISyntaxException e) {
            logger.error("Could not URL convert to URI", e);
        }
        return false;
    }
public boolean isDirectoryURL(URL url) {
        try {
            return url.getProtocol().equals("file") && new File(url.toURI()).isDirectory();
        } catch (URISyntaxException e) {
            logger.error("Could not URL convert to URI", e);
        }
        return false;
    }
Check the URL is a directory.
With war style deployment, AssetsController exposes the file list of assets directories.
For example, a request to http://localhost:8080/assets/css/ displays the file list of css directory.
So this method checks the URL is a directory.

@param url A URL of assets
@return true if the URL is a directory