public void checkValidity(){
		if (rootUrl == null) throw new IllegalArgumentException("rootUrl is not set!");
		if (sourceDir == null) throw new IllegalArgumentException("sourceDir is not set!");
		if (!sourceDir.exists()) throw new IllegalArgumentException("sourceDir does not exist!");
		if (!sourceDir.isDirectory()) throw new IllegalArgumentException("sourceDir is not a directory!");
		if (targetDir == null) throw new IllegalArgumentException("targetDir is not set!");
		
		if (dataDir != null){
			if (dataUrl == null) throw new IllegalArgumentException("if dataDir is set, dataUrl must be set also!");
		}
	}