(Java) Refresh Access Token on 401 Unauthorized and Retry (Service Account)

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Demonstrates how to handle an expired access token error, refresh the token, and retry the request. (In this case, the request is to download an object from Google Cloud Storage.)

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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.

    // This example uses a previously obtained access token having permission for the 
    // scope "https://www.googleapis.com/auth/cloud-platform"

    // In this example, Get Google Cloud Storage OAuth2 Access Token, 
    // the service account access token was saved to a text file.  This example fetches the access token from the file..
    CkStringBuilder sbToken = new CkStringBuilder();
    boolean success = sbToken.LoadFile("qa_data/tokens/googleCloudStorageAccessToken.txt","utf-8");
    if (success == false) {
        System.out.println("Failed to load access token.");
        return;
        }

    CkHttp http = new CkHttp();

    http.put_AuthToken(sbToken.getAsString());

    // Construct a URL to download an object named "starfish.jpg" from the "chilkat-ocean" bucket.
    http.SetUrlVar("bucket_name","chilkat-ocean");
    http.SetUrlVar("object_name","starfish.jpg");
    String url = "https://www.googleapis.com/storage/v1/b/{$bucket_name}/o/{$object_name}?alt=media";

    // If there is an error response, then we didn't actually download the file data,
    // but instead we downloaded an error response..
    CkBinData fileData = new CkBinData();
    success = http.DownloadBd(url,fileData);
    int responseCode = http.get_LastStatus();
    if ((success == false) && (responseCode != 401)) {
        System.out.println(http.lastErrorText());
        return;
        }

    if (responseCode == 401) {
        System.out.println("Received 401 Unauthorized response. Attempting to refresh the access token...");

        // May be that the access token expired.
        // Load our JSON key and request a new access token, then retry the original request.
        CkFileAccess fac = new CkFileAccess();
        String jsonKey = fac.readEntireTextFile("qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json","utf-8");
        if (fac.get_LastMethodSuccess() != true) {
            System.out.println(fac.lastErrorText());
            return;
            }

        CkAuthGoogle gAuth = new CkAuthGoogle();
        gAuth.put_JsonKey(jsonKey);
        gAuth.put_Scope("https://www.googleapis.com/auth/cloud-platform");
        gAuth.put_ExpireNumSeconds(3600);
        gAuth.put_SubEmailAddress("");

        CkSocket tlsSock = new CkSocket();
        success = tlsSock.Connect("www.googleapis.com",443,true,5000);
        if (success != true) {
            System.out.println(tlsSock.lastErrorText());
            return;
            }

        success = gAuth.ObtainAccessToken(tlsSock);
        if (success != true) {
            System.out.println(gAuth.lastErrorText());
            return;
            }

        fac.WriteEntireTextFile("qa_data/tokens/googleCloudStorageAccessToken.txt",gAuth.accessToken(),"utf-8",false);

        // Retry the original request.
        http.put_AuthToken(gAuth.accessToken());
        success = http.DownloadBd(url,fileData);
        if (success == false) {
            System.out.println(http.lastErrorText());
            return;
            }

        }

    if (responseCode != 200) {
        // Get the error response
        CkStringBuilder sbErrorResponse = new CkStringBuilder();
        sbErrorResponse.AppendBd(fileData,"utf-8",0,0);
        System.out.println("Error response code = " + responseCode);
        System.out.println("Error:");
        System.out.println(sbErrorResponse.getAsString());
        return;
        }

    System.out.println("Success.");

    // Save the downloaded data to a file.
    success = fileData.WriteFile("qa_output/starfish.jpg");
  }
}