(Java) S3 Get Object Metadata, such as ETag

Demonstrates how to get an S3 object's metadata using a HEAD request.

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import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    CkRest rest = new CkRest();

    // Connect to the Amazon AWS REST server in the desired region.
    // In this case we connect to S3 in the "us-west-2" region.
    boolean bTls = true;
    int port = 443;
    boolean bAutoReconnect = true;
    boolean success = rest.Connect("s3-us-west-2.amazonaws.com",port,bTls,bAutoReconnect);

    // Provide AWS credentials.
    CkAuthAws authAws = new CkAuthAws();
    authAws.put_AccessKey("AWS_ACCESS_KEY");
    authAws.put_SecretKey("AWS_SECRET_KEY");
    authAws.put_ServiceName("s3");

    // This particular bucket is in the Oregon region, as opposed to the US Standard,
    // therefore the Region must be set appropriately.
    // Also note that we connected to "s3-us-west-2.amazonaws.com".
    authAws.put_Region("us-west-2");

    success = rest.SetAuthAws(authAws);

    // Note: The above REST connection and setup of the AWS credentials
    // can be done once.  After connecting, any number of REST calls can be made.
    // The "auto reconnect" property passed to rest.Connect indicates that if
    // the connection is lost, a REST method call will automatically reconnect
    // if needed.
    // --------------------------------------------------------------------------

    // Set the bucket name via the HOST header.
    // In this case, the bucket name is "chilkat.ocean".
    // Note that the Host header should use "bucketName.s3.amazonaws.com", not "bucketName.s3-us-west-2.amazonaws.com"
    rest.put_Host("chilkat.ocean.s3.amazonaws.com");

    // Our object is "starfish.jpg".
    // Get the metadata.
    // Since we are sending a HEAD request, we shouldn't use any of the Full* methods.
    // Instead, send the request, then just read the response header.
    success = rest.SendReqNoBody("HEAD","/starfish.jpg");
    if (success != true) {
        System.out.println(rest.lastErrorText());
        return;
        }

    // Now get the response header.
    int statusCode = rest.ReadResponseHeader();
    if (statusCode < 0) {
        System.out.println(rest.lastErrorText());
        return;
        }

    // When successful, the S3 Storage service will respond with a 200 response code,
    // with an XML body.  
    if (statusCode != 200) {
        // Examine the request/response to see what happened.
        System.out.println("response status code = " + statusCode);
        System.out.println("response status text = " + rest.responseStatusText());
        System.out.println("response header: " + rest.responseHeader());
        return;
        }

    // The response header contains information about the S3 object.
    // For example:

    // 	HTTP/1.1 200 OK
    // 	x-amz-id-2: GrV/hrB2EUkBlWc0h3JDdmVIrYDXfPC7CGvo/qSVRmYRPwilAOry8+4r2YWl4xJfa1HRYXrP808=
    // 	x-amz-request-id: 4BDC6D6AEA0BDEF3
    // 	Date: Mon, 13 May 2019 22:03:13 GMT
    // 	Last-Modified: Mon, 10 Nov 2014 16:10:23 GMT
    // 	ETag: "2e9c59dbf2662367dc97dfdda85da048"
    // 	Accept-Ranges: bytes
    // 	Content-Type: image/jpg
    // 	Content-Length: 6229
    // 	Server: AmazonS3

    // Get the ETag response header value:
    String etag = rest.responseHdrByName("ETag");
    System.out.println("ETag: " + etag);
  }
}