[RESOLVIDO]Gravar em XML sem apagar o que havia - XStream

public static void gerarXml(Local local) throws FileNotFoundException {
        XStream xStream = new XStream();
        //Usamos o método que detecta as classes anotadas
        xStream.autodetectAnnotations(true);
        
        String documento = xStream.toXML(local);
        salvarArquivo(xStream.toXML(local), "localXml.xml");
    }

    private static void lerXmlAnnotation() {
        FileReader reader = null;
        try {
            //carrega o arquivo XML para um objeto reader
            reader = new FileReader(
            "C:\\DengueXMLArquivos\\localXml.xml"
            );
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        //Cria o objeto xstream
        XStream xStream = new XStream(new DomDriver());
        //Para ler vamos utilizar outro método o
        //processAnnotations() e como parâmetro passamos
        //a classe que possui as anotações
        xStream.processAnnotations(Local.class);

        Local local = (Local) xStream.fromXML(reader);
        System.out.println(local.toString());
    }
	
    private static void salvarArquivo(String documento, String file) {
        File path = new File("C:\\DengueXMLArquivos\\" + file);
        try {
            PrintWriter writer = new PrintWriter(path);
            writer.println(
            "<?xml version=\"1.0\" encoding=\"ISO-8859-1\" standalone=\"no\"?>"
            );           
            writer.println(documento);
            writer.flush();
            writer.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }     

    }