class JwtTokenUtil {
    private static final Logger LOGGER = LoggerFactory.getLogger(JwtTokenUtil.class);
    private static final String CLAIM_KEY_USERNAME = "sub";
    private static final String CLAIM_KEY_CREATED = "created";
    @Value("${jwt.secret}")
    private String secret;
    @Value("${jwt.expiration}")
    private Long expiration;
    @Value("${jwt.tokenHead}")
    private String tokenHead;

    /**
     * 根据负责生成JWT的token
     */
    private String generateToken(Map<String, Object> claims) {
        return Jwts.builder()
                .setClaims(claims)
                .setExpiration(generateExpirationDate())
                .signWith(SignatureAlgorithm.HS512, secret)
                .compact();
    }

    /**
     * 从token中获取JWT中的负载
     */
    private Claims getClaimsFromToken(String token) {
        Claims claims = null;
        try {
            claims = Jwts.parser()
                    .setSigningKey(secret)
                    .parseClaimsJws(token)
                    .getBody();
        } catch (Exception e) {
            LOGGER.info("JWT格式验证失败:{}", token);
        }
        return claims;
    }

    /**
     * 生成token的过期时间
     */
    private Date generateExpirationDate() {
        return new Date(System.currentTimeMillis() + expiration * 1000);
    }

    /**
     * 从token中获取登录用户名
     */
    public String getUserNameFromToken(String token) {<FILL_FUNCTION_BODY>}

    /**
     * 验证token是否还有效
     *
     * @param token       客户端传入的token
     * @param userDetails 从数据库中查询出来的用户信息
     */
    public boolean validateToken(String token, UserDetails userDetails) {
        String username = getUserNameFromToken(token);
        return username.equals(userDetails.getUsername()) && !isTokenExpired(token);
    }

    /**
     * 判断token是否已经失效
     */
    private boolean isTokenExpired(String token) {
        Date expiredDate = getExpiredDateFromToken(token);
        return expiredDate.before(new Date());
    }

    /**
     * 从token中获取过期时间
     */
    private Date getExpiredDateFromToken(String token) {
        Claims claims = getClaimsFromToken(token);
        return claims.getExpiration();
    }

    /**
     * 根据用户信息生成token
     */
    public String generateToken(UserDetails userDetails) {
        Map<String, Object> claims = new HashMap<>();
        claims.put(CLAIM_KEY_USERNAME, userDetails.getUsername());
        claims.put(CLAIM_KEY_CREATED, new Date());
        return generateToken(claims);
    }

    /**
     * 当原来的token没过期时是可以刷新的
     *
     * @param oldToken 带tokenHead的token
     */
    public String refreshHeadToken(String oldToken) {
        if(StrUtil.isEmpty(oldToken)){
            return null;
        }
        String token = oldToken.substring(tokenHead.length());
        if(StrUtil.isEmpty(token)){
            return null;
        }
        //token校验不通过
        Claims claims = getClaimsFromToken(token);
        if(claims==null){
            return null;
        }
        //如果token已经过期，不支持刷新
        if(isTokenExpired(token)){
            return null;
        }
        //如果token在30分钟之内刚刷新过，返回原token
        if(tokenRefreshJustBefore(token,30*60)){
            return token;
        }else{
            claims.put(CLAIM_KEY_CREATED, new Date());
            return generateToken(claims);
        }
    }

    /**
     * 判断token在指定时间内是否刚刚刷新过
     * @param token 原token
     * @param time 指定时间（秒）
     */
    private boolean tokenRefreshJustBefore(String token, int time) {
        Claims claims = getClaimsFromToken(token);
        Date created = claims.get(CLAIM_KEY_CREATED, Date.class);
        Date refreshDate = new Date();
        //刷新时间在创建时间的指定时间内
        if(refreshDate.after(created)&&refreshDate.before(DateUtil.offsetSecond(created,time))){
            return true;
        }
        return false;
    }
}

        String username;
        try {
            Claims claims = getClaimsFromToken(token);
            username = claims.getSubject();
        } catch (Exception e) {
            username = null;
        }
        return username;
    
<no_super_class>