public class TokenProcessor {
 private long privious;// 上次生成表單標識號得時間值
 private static TokenProcessor instance = new TokenProcessor();
 public static String FORM_TOKEN_KEY = "FORM_TOKEN_KEY";
 private TokenProcessor() {
 }
 public static TokenProcessor getInstance() {
  return instance;
 }
 /**
  * 驗證請求中得標識號是否有效，如果請求中的表單標識與當前用戶session中的相同，返回結果true=
  */
 public synchronized boolean isTokenValid(HttpServletRequest request) {
  // 為避免session對象不存在時候創建Session對象
  HttpSession session = request.getSession(false);
  if (session == null) {
   return false;
  }
  String saved = (String) session.getAttribute(FORM_TOKEN_KEY);
  if (saved == null) {
   return false;
  }
  String token = (String) request.getParameter(FORM_TOKEN_KEY);
  if (token == null) {
   return false;
  }
  return saved.equals(token);
 }
 /**
  * 驗證請求中得標識號是否有效，如果請求中的表單標識與當前用戶session中的相同，返回結果true=
  */
 public synchronized boolean isTokenValid(HttpServletRequest request,String token) {
  // 未避免session對象不存在時候創建Session對象
  HttpSession session = request.getSession(false);
  if (session == null) {
   return false;
  }
  String saved = (String) session.getAttribute(FORM_TOKEN_KEY);
  if (saved == null) {
   return false;
  }
  if (token == null) {
   return false;
  }
  return saved.equals(token);
 }
 /**
  * 清除存儲在當前用戶session中的表單標識號
  */
 public synchronized void reset(HttpServletRequest request) {
  HttpSession session = request.getSession(false);
  if (session == null) {
   return;
  }
  session.removeAttribute(FORM_TOKEN_KEY);
 }
 /**
  * 產生表單標識號并將之保存在當前用戶得session中
  */
 public synchronized void saveToken(HttpServletRequest request) {
  HttpSession session = request.getSession();
  try {
   byte id[] = session.getId().getBytes();
   long current = System.currentTimeMillis();
   if (current == privious) {
    current++;
   }
   privious = current;
   byte now[] = String.valueOf(current).getBytes();
   MessageDigest md = MessageDigest.getInstance("MD5");
   md.update(id);
   md.update(now);
   String token = toHex(md.digest());
   session.setAttribute(FORM_TOKEN_KEY, token);
  } catch (NoSuchAlgorithmException e) {
  }
 }
 /**
  * 將一個字節數轉換成十六進制得字符串
  */
 public String toHex(byte buffer[]) {
  StringBuffer sb = new StringBuffer(buffer.length * 2);
  for (int i = 0; i < buffer.length; i++) {
   sb.append(Character.forDigit((buffer[i] & 0x60) >> 4, 16));
   sb.append(Character.forDigit(buffer[i] & 0x0f, 16));
  }
  return sb.toString();
 }
}