The best place to store files like this would be in your application’s resources folder. When the application is deployed these are copied into the deployment directory structure.
To access these from a Java Action you need to use the Core.getConfiguration().getResourcesPath() method. For example...
String filePath = Core.getConfiguration().getResourcesPath() + File.separator + filename;
Hope this helps.
In addition to the previous answer, I believe the filepath on the cloud has forward slashes / instead of backslashes \. So you can try using forward slashes in the path.