(Java) Google Calendar -- Refresh an Expired Access Token

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Demonstrates how to refresh an expired access token. If a Google Calendar REST API call results in a 401 "unauthorized" response, then it is likely the access token expired. An application should be able to automatically refresh the access token with no user interaction and then re-try the request with the newly obtained access token.

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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.

    // It is assumed we previously obtained an OAuth2 access token.
    // This example loads the JSON access token file 
    // saved by this example: Get Google Calendar OAuth2 Access Token

    CkJsonObject jsonToken = new CkJsonObject();
    boolean success = jsonToken.LoadFile("qa_data/tokens/googleCalendar.json");
    if (success != true) {
        System.out.println("Failed to load googleCalendar.json");
        return;
        }

    // The access token JSON looks like this:

    // 	{ 
    // 	 "access_token": "abac.Ci-ZabcdF37-NUrmSzxbHxTsMbtlN-uPfabcdAQN_2ekzj0s5ofCzRabcdTDMGaa2Q",
    // 	 "token_type": "Bearer",
    // 	 "expires_in": 3600,
    // 	 "refresh_token": "1/lEe5abcdNJ77eOSDBabcdkQGVmDalkwabcdR2Hatbo"
    // 	}
    // 

    CkOAuth2 oauth2 = new CkOAuth2();

    oauth2.put_TokenEndpoint("https://www.googleapis.com/oauth2/v4/token");

    // Replace these with actual values.
    oauth2.put_ClientId("GOOGLE-CLIENT-ID");
    oauth2.put_ClientSecret("GOOGLE-CLIENT-SECRET");

    // Get the "refresh_token"
    oauth2.put_RefreshToken(jsonToken.stringOf("refresh_token"));

    // Send the HTTP POST to refresh the access token..
    success = oauth2.RefreshAccessToken();
    if (success != true) {
        System.out.println(oauth2.lastErrorText());
        return;
        }

    // The response contains a new access token, but we must keep
    // our existing refresh token for when we need to refresh again in the future.
    jsonToken.UpdateString("access_token",oauth2.accessToken());

    // Save the new JSON access token response to a file.
    CkStringBuilder sbJson = new CkStringBuilder();
    jsonToken.put_EmitCompact(false);
    jsonToken.EmitSb(sbJson);
    sbJson.WriteFile("qa_data/tokens/googleCalendar.json","utf-8",false);

    System.out.println("OAuth2 authorization granted!");
    System.out.println("New Access Token = " + oauth2.accessToken());
  }
}