@Order(SessionRepositoryFilter.DEFAULT_ORDER)
public class SessionRepositoryFilter<S extends Session> extends OncePerRequestFilter {
    @Override
  protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException {
    request.setAttribute(SESSION_REPOSITORY_ATTR, this.sessionRepository);
         //使用HttpServletRequest 、HttpServletResponse和servletContext创建一个SessionRepositoryRequestWrapper
    SessionRepositoryRequestWrapper wrappedRequest = new SessionRepositoryRequestWrapper(
        request, response, this.servletContext);
    SessionRepositoryResponseWrapper wrappedResponse = new SessionRepositoryResponseWrapper(
        wrappedRequest, response);
    try {
      filterChain.doFilter(wrappedRequest, wrappedResponse);
    }
    finally {
            //保存session信息
      wrappedRequest.commitSession();
    }
  }
}
@Override
    public HttpSessionWrapper getSession(boolean create) {
            //获取当前Request作用域中代表Session的属性，缓存作用避免每次都从sessionRepository获取
      HttpSessionWrapper currentSession = getCurrentSession();
      if (currentSession != null) {
        return currentSession;
      }
            //查找客户端中一个叫SESSION的cookie，拿到sessionId，通过sessionRepository对象根据sessionId去Redis中查找
      S requestedSession = getRequestedSession();
            //如果从redis中查询到了值
      if (requestedSession != null) {
                //客户端存在sessionId 并且未过期
        if (getAttribute(INVALID_SESSION_ID_ATTR) == null) {
          requestedSession.setLastAccessedTime(Instant.now());
          this.requestedSessionIdValid = true;
          currentSession = new HttpSessionWrapper(requestedSession, getServletContext());
          currentSession.setNew(false);
                    //将Session设置到request属性中
          setCurrentSession(currentSession);
          return currentSession;
        }
      }
      else {
        // This is an invalid session id. No need to ask again if
        // request.getSession is invoked for the duration of this request
        if (SESSION_LOGGER.isDebugEnabled()) {
          SESSION_LOGGER.debug(
              "No session found by id: Caching result for getSession(false) for this HttpServletRequest.");
        }
        setAttribute(INVALID_SESSION_ID_ATTR, "true");
      }
            //不创建Session就直接返回null
      if (!create) {
        return null;
      }
      if (SESSION_LOGGER.isDebugEnabled()) {
        SESSION_LOGGER.debug(
            "A new session was created. To help you troubleshoot where the session was created we provided a StackTrace (this is not an error). You can prevent this from appearing by disabling DEBUG logging for "
                + SESSION_LOGGER_NAME,
            new RuntimeException(
                "For debugging purposes only (not an error)"));
      }
            //执行到这了说明需要创建新的Session
            // 通过sessionRepository创建RedisSession这个对象
      S session = SessionRepositoryFilter.this.sessionRepository.createSession();
      session.setLastAccessedTime(Instant.now());
      currentSession = new HttpSessionWrapper(session, getServletContext());
      setCurrentSession(currentSession);
      return currentSession;
    }
  // 通过sessionRepository创建RedisSession这个对象
  @Override
  public RedisSession createSession() {
    Duration maxInactiveInterval = Duration
        .ofSeconds((this.defaultMaxInactiveInterval != null)
            ? this.defaultMaxInactiveInterval
            : MapSession.DEFAULT_MAX_INACTIVE_INTERVAL_SECONDS);
    RedisSession session = new RedisSession(maxInactiveInterval);
    session.flushImmediateIfNecessary();
    return session;
  }

 /**
     *    会员注册
     */
    @Override
    public void register(MemberUserRegisterVo vo) {
        MemberEntity memberEntity = new MemberEntity();
        //设置默认等级
        MemberLevelEntity levelEntity = memberLevelDao.getDefaultLevel();
        memberEntity.setLevelId(levelEntity.getId());
        //设置其它的默认信息
        //检查用户名和手机号是否唯一。感知异常，异常机制（异常机制就是问题就抛出具体异常，没问题就继续执行下面的语句）
        checkPhoneUnique(vo.getPhone());
        checkUserNameUnique(vo.getUserName());
        memberEntity.setNickname(vo.getUserName());
        memberEntity.setUsername(vo.getUserName());
        //密码进行MD5盐值加密（盐值加密同一个数据的每次加密结果是不一样的，通过match方法来密码校验）
        // （注意这里不能用md5直接加密放数据库，因为彩虹表可以破解md5，所谓彩虹表就是通过大量的md5数据反向退出md5
        // 注意MD5是不可逆，但是可暴力通过彩虹表破解）
        BCryptPasswordEncoder bCryptPasswordEncoder = new BCryptPasswordEncoder();
        String encode = bCryptPasswordEncoder.encode(vo.getPassword());
        memberEntity.setPassword(encode);
        memberEntity.setMobile(vo.getPhone());
        memberEntity.setGender(0);
        memberEntity.setCreateTime(new Date());
        //保存数据
        this.baseMapper.insert(memberEntity);
    }
    /**
     * 检查手机号是否重复的异常机制方法
     * @param phone
     * @throws PhoneException
     */
    @Override
    public void checkPhoneUnique(String phone) throws PhoneException {
        Long phoneCount = this.baseMapper.selectCount(new QueryWrapper<MemberEntity>().eq("mobile", phone));
        //usernameCount > 0表示手机号已经存在
        if (phoneCount > 0) {
            throw new PhoneException();
        }
    }
    /**
     * 检查用户名是否重复的异常机制方法
     * @param userName
     * @throws UsernameException
     */
    @Override
    public void checkUserNameUnique(String userName) throws UsernameException {
        Long usernameCount = this.baseMapper.selectCount(new QueryWrapper<MemberEntity>().eq("username", userName));
        //usernameCount > 0表示用户名已经存在
        if (usernameCount > 0) {
            throw new UsernameException();
        }
    }