[Java] Access the signed URL of s3 (signed version 2)

I will follow the official page of aws. https://docs.aws.amazon.com/ja_jp/AmazonS3/latest/dev/RESTAuthentication.html

In the authentication header Authorization: AWS AWSAccessKeyId:Signature However, it is quite troublesome to make this Signature.

I happened to use it in a Java project, so I'll post it instead of a memo.

This time, https://[BUCKET].[ENDPOINT]/[FILE_NAME] I am accessing with a certificate.

  protected void getFile() throws NoSuchAlgorithmException, InvalidKeyException, ClientProtocolException, IOException {

    String resource= "/" + BUCKET + "/" +FILE_NAME;
    String contentType = "application/octet-stream";
    String md5 = "";
    String daHeader = "x-amz-meta-user:" + USER_ID;
    Calendar c = Calendar.getInstance(TimeZone.getTimeZone("UTC"));
    SimpleDateFormat df = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss Z", Locale.ENGLISH);
    //Creating a StringToSign
    String now = df.format(c.getTime());
    String stringToSign="GET" + "\n" + md5 + "\n" + contentType + "\n" + now + "\n" + daHeader + "\n" + resource;

    //Creating a signature
    SecretKeySpec sk = new SecretKeySpec(S3_SECRET.getBytes(), "HmacSHA1");
    Mac mac = Mac.getInstance("HmacSHA1");
    byte[] dataBytes = stringToSign.getBytes("UTF-8");
    byte[] signatureBytes = mac.doFinal(dataBytes);
    String signature = new String(Base64.encodeBase64(signatureBytes), "UTF-8");

    //Get request
    HttpClient client = HttpClientBuilder.create().build(); 
    HttpGet request = new HttpGet("https://" + BUCKET + '.' + END_POINT + "/" + FILE_NAME);
    request.setHeader("Host", BUCKET + '.' + END_POINT);
    request.setHeader("Date", now.toString());
    request.setHeader("Content-Type", contentType);
    request.setHeader("Authorization", "AWS" + " " + S3_KEY + ':' + signature);
    request.setHeader("x-amz-meta-user", USER_ID);        
    HttpResponse response = client.execute(request);      

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