Android获取apk的证书MD5值

public static String getSignMd5Str(){
    try {
        PackageManager packageManager = this.getPackageManager();
        PackageInfo packageInfo = packageManager.getPackageInfo(this.getPackageName(), PackageManager.GET_SIGNATURES);
        Signature[] signs = packageInfo.signatures;
        Signature sign = signs[0];
        String signStr = encryptionMD5(sign.toByteArray());
        return signStr;
    } catch (NameNotFoundException e) {
        e.printStackTrace();
    }
    return "";
}

private static String encryptionMD5(byte[] bytestr){
    MessageDigest messageDigest = null;
    StringBuffer md5StrBuff= new StringBuffer();
    try {
        messageDigest = MessageDigest.getInstance("MD5");
        messageDigest.reset();
        messageDigest.update(bytestr);
        byte[] byteArray = messageDigest.digest();
        for ( int i = 0; i < byteArray.length; i++){
            if (Integer.toHexString(0xFF & byteArray[i]).length()==1){
                md5StrBuff.append("0").append(Integer.toHexString(0xFF & byteArray[i]));
            }else {
                md5StrBuff.append(Integer.toHexString(0xFF & byteArray[i]));
            }
        }
    } catch (NoSuchAlgorithmException e) {
        e.printStackTrace();
    }
    return md5StrBuff.toString();
}