Java Quickstart

Complete the steps described in the rest of this page, and in about five minutes you'll have a simple Java command-line application that makes requests to the Google Calendar API.

Prerequisites

To run this quickstart, you'll need:

  • Java 1.7 or greater.
  • Gradle 2.3 or greater.
  • Access to the internet and a web browser.
  • A Google account with Google Calendar enabled.

Step 1: Turn on the Google Calendar API

  1. Use this wizard to create or select a project in the Google Developers Console and automatically turn on the API. Click Continue, then Go to credentials.
  2. On the Add credentials to your project page, click the Cancel button.
  3. At the top of the page, select the OAuth consent screen tab. Select an Email address, enter a Product name if not already set, and click the Save button.
  4. Select the Credentials tab, click the Create credentials button and select OAuth client ID.
  5. Select the application type Other, enter the name "Google Calendar API Quickstart", and click the Create button.
  6. Click OK to dismiss the resulting dialog.
  7. Click the file_download (Download JSON) button to the right of the client ID.
  8. Move this file to your working directory and rename it client_secret.json.

Step 2: Prepare the project

  1. In your working directory, run the following commands to create a new project structure:
gradle init --type basic
mkdir -p src/main/java src/main/resources 
  1. Copy the client_secret.json file you downloaded in Step 1 into the src/main/resources/ directory you just created.
  2. Open the default build.gradle file and replace its contents with the following code:

Step 3: Set up the sample

Create a file named src/main/java/Quickstart.java and copy in the following code:



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.HttpTransport;
import com.google.api.client.json.jackson2.JacksonFactory;
import com.google.api.client.json.JsonFactory;
import com.google.api.client.util.store.FileDataStoreFactory;
import com.google.api.client.util.DateTime;

import com.google.api.services.calendar.CalendarScopes;
import com.google.api.services.calendar.model.*;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.List;

public class Quickstart {
    /** Application name. */
    private static final String APPLICATION_NAME =
        "Google Calendar API Java Quickstart";

    /** Directory to store user credentials for this application. */
    private static final java.io.File DATA_STORE_DIR = new java.io.File(
        System.getProperty("user.home"), ".credentials/calendar-java-quickstart");

    /** Global instance of the {@link FileDataStoreFactory}. */
    private static FileDataStoreFactory DATA_STORE_FACTORY;

    /** Global instance of the JSON factory. */
    private static final JsonFactory JSON_FACTORY =
        JacksonFactory.getDefaultInstance();

    /** Global instance of the HTTP transport. */
    private static HttpTransport HTTP_TRANSPORT;

    /** Global instance of the scopes required by this quickstart.
     *
     * If modifying these scopes, delete your previously saved credentials
     * at ~/.credentials/calendar-java-quickstart
     */
    private static final List<String> SCOPES =
        Arrays.asList(CalendarScopes.CALENDAR_READONLY);

    static {
        try {
            HTTP_TRANSPORT = GoogleNetHttpTransport.newTrustedTransport();
            DATA_STORE_FACTORY = new FileDataStoreFactory(DATA_STORE_DIR);
        } catch (Throwable t) {
            t.printStackTrace();
            System.exit(1);
        }
    }

    /**
     * Creates an authorized Credential object.
     * @return an authorized Credential object.
     * @throws IOException
     */
    public static Credential authorize() throws IOException {
        // Load client secrets.
        InputStream in =
            Quickstart.class.getResourceAsStream("/client_secret.json");
        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(DATA_STORE_FACTORY)
                .setAccessType("offline")
                .build();
        Credential credential = new AuthorizationCodeInstalledApp(
            flow, new LocalServerReceiver()).authorize("user");
        System.out.println(
                "Credentials saved to " + DATA_STORE_DIR.getAbsolutePath());
        return credential;
    }

    /**
     * Build and return an authorized Calendar client service.
     * @return an authorized Calendar client service
     * @throws IOException
     */
    public static com.google.api.services.calendar.Calendar
        getCalendarService() throws IOException {
        Credential credential = authorize();
        return new com.google.api.services.calendar.Calendar.Builder(
                HTTP_TRANSPORT, JSON_FACTORY, credential)
                .setApplicationName(APPLICATION_NAME)
                .build();
    }

    public static void main(String[] args) throws IOException {
        // Build a new authorized API client service.
        // Note: Do not confuse this class with the
        //   com.google.api.services.calendar.model.Calendar class.
        com.google.api.services.calendar.Calendar service =
            getCalendarService();

        // 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.size() == 0) {
            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);
            }
        }
    }

}

Step 4: Run the sample

Build and run the quickstart with the command:

gradle -q run

The first time you run the sample, it will prompt you to authorize access:

  1. The sample will attempt to open a new window or tab in your default browser. If this fails, copy the URL from the console and manually open it in your browser.

    If you are not already logged into your Google account, you will be prompted to log in. If you are logged into multiple Google accounts, you will be asked to select one account to use for the authorization.

  2. Click the Accept button.
  3. The sample will proceed automatically, and you may close the window/tab.

Notes

  • Authorization information is stored on the file system, so subsequent executions will not prompt for authorization.
  • The authorization flow in this example is designed for a command-line application. For information on how to perform authorization in a web application, see Using OAuth 2.0 for Web Server Applications.

Further reading

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Google Calendar API
Google Calendar API