String xml = "<?xml version="1.0" standalone="yes"?><root></root>"

String xml = "<root></root>

try (Socket socket = server.accept()) {
    try (InputStream in = socket.getInputStream()) {
        final Scanner scanner = new Scanner(new InputStreamReader(in, "UTF-8"));
        scanner.useDelimiter("<\?xml.*?\?>");  //Stop stream read when XMl tag is found
    }
}