public static JwtAccount parseJwt(String jwt, String appKey) throws ExpiredJwtException, UnsupportedJwtException, MalformedJwtException, SignatureException, IllegalArgumentException {
        Claims claims = Jwts.parser()
                .setSigningKey(DatatypeConverter.parseBase64Binary(appKey))
                 //在这一行会抛出SignatureException被jwtMatcher捕获到
                .parseClaimsJws(jwt)
                .getBody();

public boolean isValid(byte[] data, byte[] signature) {
        byte[] computed = this.signer.sign(data);
    	//这里的this.signer是macSigner alg=HS512 
        return MessageDigest.isEqual(computed, signature);
    }