Java quickstart

Quickstarts explain how to set up and run an app that calls a Google Workspace API.

Google Workspace quickstarts use the API client libraries to handle some details of the authentication and authorization flow. We recommend that you use the client libraries for your own apps. Before you can run the sample app, each quickstart requires that you turn on authentication and authorization. If you're unfamiliar with authentication and authorization for Google Workspace APIs, read the Authentication and authorization overview.

Create a Java command-line application that makes requests to the Google Calendar API.

Objectives

  • Set up your environment.
  • Set up the sample.
  • Run the sample.

Prerequisites

  • A Google account with Google Calendar enabled.

Set up your environment

To complete this quickstart, set up your environment.

Enable the API

Before using Google APIs, you need to turn them on in a Google Cloud project. You can turn on one or more APIs in a single Google Cloud project.
  • In the Google Cloud console, enable the Google Calendar API.

    Enable the API

Authorize credentials for a desktop application

To authenticate as an end user and access user data in your app, you need to create one or more OAuth 2.0 Client IDs. A client ID is used to identify a single app to Google's OAuth servers. If your app runs on multiple platforms, you must create a separate client ID for each platform.
  1. In the Google Cloud console, go to Menu > APIs & Services > Credentials.

    Go to Credentials

  2. Click Create Credentials > OAuth client ID.
  3. Click Application type > Desktop app.
  4. In the Name field, type a name for the credential. This name is only shown in the Google Cloud console.
  5. Click Create. The OAuth client created screen appears, showing your new Client ID and Client secret.
  6. Click OK. The newly created credential appears under OAuth 2.0 Client IDs.
  7. Save the downloaded JSON file as credentials.json, and move the file to your working directory.

Prepare the workspace

  1. In your working directory, create a new project structure:

    gradle init --type basic
    mkdir -p src/main/java src/main/resources 
    
  2. In the src/main/resources/ directory, copy the credentials.json file that you previously downloaded.

  3. Open the default build.gradle file and replace its contents with the following code:

    calendar/quickstart/build.gradle
    apply plugin: 'java'
    apply plugin: 'application'
    
    mainClassName = 'CalendarQuickstart'
    sourceCompatibility = 11
    targetCompatibility = 11
    version = '1.0'
    
    repositories {
        mavenCentral()
    }
    
    dependencies {
        implementation 'com.google.api-client:google-api-client:2.0.0'
        implementation 'com.google.oauth-client:google-oauth-client-jetty:1.34.1'
        implementation 'com.google.apis:google-api-services-calendar:v3-rev20220715-2.0.0'
    }
    

Set up the sample

  1. In the src/main/java/ directory, create a new Java file with a name that matches the mainClassName value in your build.gradle file.

  2. Include the following code in your new Java file:

    calendar/quickstart/src/main/java/CalendarQuickstart.java
    import com.google.api.client.auth.oauth2.Credential;
    import com.google.api.client.extensions.java6.auth.oauth2.AuthorizationCodeInstalledApp;
    import com.google.api.client.extensions.jetty.auth.oauth2.LocalServerReceiver;
    import com.google.api.client.googleapis.auth.oauth2.GoogleAuthorizationCodeFlow;
    import com.google.api.client.googleapis.auth.oauth2.GoogleClientSecrets;
    import com.google.api.client.googleapis.javanet.GoogleNetHttpTransport;
    import com.google.api.client.http.javanet.NetHttpTransport;
    import com.google.api.client.json.JsonFactory;
    import com.google.api.client.json.gson.GsonFactory;
    import com.google.api.client.util.DateTime;
    import com.google.api.client.util.store.FileDataStoreFactory;
    import com.google.api.services.calendar.Calendar;
    import com.google.api.services.calendar.CalendarScopes;
    import com.google.api.services.calendar.model.Event;
    import com.google.api.services.calendar.model.Events;
    
    import java.io.FileNotFoundException;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.InputStreamReader;
    import java.security.GeneralSecurityException;
    import java.util.Collections;
    import java.util.List;
    
    /* class to demonstarte use of Calendar events list API */
    public class CalendarQuickstart {
      /**
       * Application name.
       */
      private static final String APPLICATION_NAME = "Google Calendar API Java Quickstart";
      /**
       * Global instance of the JSON factory.
       */
      private static final JsonFactory JSON_FACTORY = GsonFactory.getDefaultInstance();
      /**
       * Directory to store authorization tokens for this application.
       */
      private static final String TOKENS_DIRECTORY_PATH = "tokens";
    
      /**
       * Global instance of the scopes required by this quickstart.
       * If modifying these scopes, delete your previously saved tokens/ folder.
       */
      private static final List<String> SCOPES =
          Collections.singletonList(CalendarScopes.CALENDAR_READONLY);
      private static final String CREDENTIALS_FILE_PATH = "/credentials.json";
    
      /**
       * Creates an authorized Credential object.
       *
       * @param HTTP_TRANSPORT The network HTTP Transport.
       * @return An authorized Credential object.
       * @throws IOException If the credentials.json file cannot be found.
       */
      private static Credential getCredentials(final NetHttpTransport HTTP_TRANSPORT)
          throws IOException {
        // Load client secrets.
        InputStream in = CalendarQuickstart.class.getResourceAsStream(CREDENTIALS_FILE_PATH);
        if (in == null) {
          throw new FileNotFoundException("Resource not found: " + CREDENTIALS_FILE_PATH);
        }
        GoogleClientSecrets clientSecrets =
            GoogleClientSecrets.load(JSON_FACTORY, new InputStreamReader(in));
    
        // Build flow and trigger user authorization request.
        GoogleAuthorizationCodeFlow flow = new GoogleAuthorizationCodeFlow.Builder(
            HTTP_TRANSPORT, JSON_FACTORY, clientSecrets, SCOPES)
            .setDataStoreFactory(new FileDataStoreFactory(new java.io.File(TOKENS_DIRECTORY_PATH)))
            .setAccessType("offline")
            .build();
        LocalServerReceiver receiver = new LocalServerReceiver.Builder().setPort(8888).build();
        Credential credential = new AuthorizationCodeInstalledApp(flow, receiver).authorize("user");
        //returns an authorized Credential object.
        return credential;
      }
    
      public static void main(String... args) throws IOException, GeneralSecurityException {
        // Build a new authorized API client service.
        final NetHttpTransport HTTP_TRANSPORT = GoogleNetHttpTransport.newTrustedTransport();
        Calendar service =
            new Calendar.Builder(HTTP_TRANSPORT, JSON_FACTORY, getCredentials(HTTP_TRANSPORT))
                .setApplicationName(APPLICATION_NAME)
                .build();
    
        // List the next 10 events from the primary calendar.
        DateTime now = new DateTime(System.currentTimeMillis());
        Events events = service.events().list("primary")
            .setMaxResults(10)
            .setTimeMin(now)
            .setOrderBy("startTime")
            .setSingleEvents(true)
            .execute();
        List<Event> items = events.getItems();
        if (items.isEmpty()) {
          System.out.println("No upcoming events found.");
        } else {
          System.out.println("Upcoming events");
          for (Event event : items) {
            DateTime start = event.getStart().getDateTime();
            if (start == null) {
              start = event.getStart().getDate();
            }
            System.out.printf("%s (%s)\n", event.getSummary(), start);
          }
        }
      }
    }

Run the sample

  1. Run the sample:

    gradle run
    
  2. The first time you run the sample, it prompts you to authorize access:

    1. If you're not already signed in to your Google Account, you're prompted to sign in. If you're signed in to multiple accounts, select one account to use for authorization.
    2. Click Accept.

    Authorization information is stored in the file system, so the next time you run the sample code, you aren't prompted for authorization.

You have successfully created your first Java application that makes requests to the Google Calendar API.

Next steps