XHTML to PDF using flying-saucer how to cache css

In my production pipeline I need to generate a few hundred PDF from HTML. For this scenario I first convert the HTML into XHTML. Than im passing the 'cleaned' XHTML and the uri to the renderer.

Since the *.css and imageFiles are equal for all the XHTML files I dont need to resolve them all the time I process a file. Im successfully using the following code for caching images. How can I cache .css files aswell? I want to avoid putting all files into my classpath.

ITextRenderer renderer = new ITextRenderer();

ResourceLoaderUserAgent callback = new ResourceLoaderUserAgent(renderer.getOutputDevice());
callback.setSharedContext(renderer.getSharedContext());

for (MyObject myObject : myObjectList) {

    OutputStream os = new FileOutputStream(tempFile);

    final DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
    documentBuilderFactory.setValidating(false);
    DocumentBuilder builder = documentBuilderFactory.newDocumentBuilder();
    org.w3c.dom.Document document = builder.parse(myObject.getLocalPath); // full path to .xhtml

    renderer.getSharedContext().setUserAgentCallback(callback);

    renderer.setDocument(document, myObject.getUri());
    renderer.layout();
    renderer.createPDF(os);

    os.flush();
    os.close();
}
    ...


private static class ResourceLoaderUserAgent extends ITextUserAgent
{
    public ResourceLoaderUserAgent(ITextOutputDevice outputDevice) {
        super(outputDevice);
    }

    protected InputStream resolveAndOpenStream(String uri) {
        InputStream is = super.resolveAndOpenStream(uri);
        System.out.println("IN resolveAndOpenStream() " + uri);

        return is;
    }
}