Java TokenProcessor令牌校验工具类

public class TokenProcessor { private long privious;// 上次生成表单标识号得时间值 private static TokenProcessor instance = new TokenProcessor(); public static String FORM_TOKEN_KEY = "FORM_TOKEN_KEY"; private TokenProcessor() { } public static TokenProcessor getInstance() {  return instance; } /**  * 验证请求中得标识号是否有效，如果请求中的表单标识与当前用户session中的相同，返回结果true=  */ public synchronized boolean isTokenValid(HttpServletRequest request) {  // 为避免session对象不存在时候创建Session对象  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); } /**  * 验证请求中得标识号是否有效，如果请求中的表单标识与当前用户session中的相同，返回结果true=  */ public synchronized boolean isTokenValid(HttpServletRequest request,String token) {  // 未避免session对象不存在时候创建Session对象  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); } /**  * 清除存储在当前用户session中的表单标识号  */ public synchronized void reset(HttpServletRequest request) {  HttpSession session = request.getSession(false);  if (session == null) {   return;  }  session.removeAttribute(FORM_TOKEN_KEY); } /**  * 产生表单标识号并将之保存在当前用户得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) {  } } /**  * 将一个字节数转换成十六进制得字符串  */ 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(); }}