(Java) Automatically Refresh Token for 401 Unauthorized

Demonstrates how to automatically refresh an access token (without user interaction) when the token expires and a 401 Unauthorized response is received.

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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.

    String tokenFilePath = "qa_data/tokens/googleCalendar.json";

    // Get our current access token.
    CkJsonObject jsonToken = new CkJsonObject();
    boolean success = jsonToken.LoadFile(tokenFilePath);
    if (jsonToken.HasMember("access_token") == false) {
        System.out.println("No access token found.");
        return;
        }

    CkHttp http = new CkHttp();
    http.put_AuthToken(jsonToken.stringOf("access_token"));

    String jsonResponse = http.quickGetStr("https://www.googleapis.com/calendar/v3/users/me/calendarList");
    if (http.get_LastMethodSuccess() != true) {

        if (http.get_LastStatus() != 401) {
            System.out.println(http.lastErrorText());
            System.out.println("----");
            System.out.println(http.lastResponseBody());
            return;
            }

        // The access token must've expired. 
        // Refresh the access token and then retry the request.
        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(tokenFilePath,"utf-8",false);

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

        // re-try the original request.
        http.put_AuthToken(oauth2.accessToken());
        jsonResponse = http.quickGetStr("https://www.googleapis.com/calendar/v3/users/me/calendarList");
        if (http.get_LastMethodSuccess() != true) {
            System.out.println(http.lastErrorText());
            return;
            }

        }

    System.out.println(jsonResponse);
    System.out.println("-----------------------------");
  }
}