Java API自动化：获取Google OAuth 2.0访问令牌的正确姿势

<dependencies>
    <!-- Google HTTP Client Library for Java -->
    <dependency>
        <groupId>com.google.api-client</groupId>
        <artifactId>google-api-client</artifactId>
        <version>1.30.10</version>
    </dependency>

    <!-- Google OAuth Client Library for Java -->
    <dependency>
        <groupId>com.google.oauth-client</groupId>
        <artifactId>google-oauth-client</artifactId>
        <version>1.30.6</version>
    </dependency>

    <!-- Google OAuth Client Library for Java (Jetty for local server receiver) -->
    <dependency>
        <groupId>com.google.oauth-client</groupId>
        <artifactId>google-oauth-client-jetty</artifactId>
        <version>1.30.6</version>
    </dependency>

    <!-- Jackson 2 for JSON parsing -->
    <dependency>
        <groupId>com.google.api-client</groupId>
        <artifactId>google-api-client-jackson2</artifactId>
        <version>1.30.10</version>
    </dependency>

    <!-- Optional: If you need specific Google API services, e.g., Calendar -->
    <!-- <dependency>
        <groupId>com.google.apis</groupId>
        <artifactId>google-api-services-calendar</artifactId>
        <version>v3-rev20230628-2.0.0</version>
    </dependency> -->
</dependencies>

{
  "web": {
    "client_id": "YOUR_CLIENT_ID.apps.googleusercontent.com",
    "project_id": "your-project-id",
    "auth_uri": "https://accounts.google.com/o/oauth2/auth",
    "token_uri": "https://oauth2.googleapis.com/token",
    "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
    "client_secret": "YOUR_CLIENT_SECRET",
    "redirect_uris": [
      "http://localhost:8888/Callback"
    ],
    "javascript_origins": [
      "http://localhost:8888"
    ]
  }
}

package com.example.googleauth;

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

import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.security.GeneralSecurityException;
import java.util.Collections;
import java.util.List;

public class GoogleTokenGenerator {

    /** 应用程序名称，用于标识用户代理。 */
    private static final String APPLICATION_NAME = "Google API Automation Tool";

    /** JSON工厂，用于解析JSON。 */
    private static final JsonFactory JSON_FACTORY = JacksonFactory.getDefaultInstance();

    /** HTTP传输，用于所有API请求。 */
    private static HttpTransport HTTP_TRANSPORT;

    /** 存储用户凭据的目录。 */
    private static final File DATA_STORE_DIR = new File(System.getProperty("user.home"), ".credentials/google-api-automation");

    /** 数据存储工厂。 */
    private static FileDataStoreFactory DATA_STORE_FACTORY;

    static {
        try {
            HTTP_TRANSPORT = GoogleNetHttpTransport.newTrustedTransport();
            DATA_STORE_FACTORY = new FileDataStoreFactory(DATA_STORE_DIR);
        } catch (GeneralSecurityException | IOException e) {
            System.err.println("Error initializing HTTP transport or data store: " + e.getMessage());
            System.exit(1);
        }
    }

    /**
     * 授权已安装的应用程序访问用户的受保护数据。
     * @param scopes 应用程序请求的OAuth范围。
     * @return 包含访问令牌和刷新令牌的凭据对象。
     * @throws IOException 如果加载客户端密钥或授权过程中发生I/O错误。
     * @throws GeneralSecurityException 如果HTTP传输初始化失败。
     */
    public static Credential authorize(List<String> scopes) throws IOException, GeneralSecurityException {
        // 1. 加载客户端密钥
        // 从资源文件 client_secrets.json 加载客户端ID和客户端密钥
        GoogleClientSecrets clientSecrets = GoogleClientSecrets.load(
                JSON_FACTORY,
                new InputStreamReader(GoogleTokenGenerator.class.getResourceAsStream("/client_secrets.json")));

        // 2. 设置授权码流程
        GoogleAuthorizationCodeFlow flow = new GoogleAuthorizationCodeFlow.Builder(
                HTTP_TRANSPORT,
                JSON_FACTORY,
                clientSecrets,
                scopes) // 指定应用程序请求的权限范围
                .setDataStoreFactory(DATA_STORE_FACTORY) // 存储用户凭据，以便下次无需重新授权
                .setAccessType("offline") // 请求刷新令牌
                .build();

        // 3. 执行授权
        // 对于桌面应用程序，使用LocalServerReceiver在本地启动一个服务器来接收授权回调
        // 授权成功后，凭据将被存储在DATA_STORE_DIR指定的目录下
        LocalServerReceiver receiver = new LocalServerReceiver.Builder().setPort(8888).build();
        return new AuthorizationCodeInstalledApp(flow, receiver).authorize("user");
    }

    public static void main(String[] args) {
        try {
            // 定义所需的权限范围，例如访问用户的日历
            // 更多范围请参考：https://developers.google.com/identity/protocols/oauth2/scopes
            List<String> scopes = Collections.singletonList("https://www.googleapis.com/auth/calendar.readonly");

            // 执行授权，获取凭据
            Credential credential = authorize(scopes);

            // 检查凭据是否成功获取
            if (credential != null && credential.getAccessToken() != null) {
                System.out.println("成功获取Google访问令牌。");
                System.out.println("Access Token: " + credential.getAccessToken());

                // 如果需要，可以获取刷新令牌
                if (credential.getRefreshToken() != null) {
                    System.out.println("Refresh Token: " + credential.getRefreshToken());
                } else {
                    System.out.println("未获取到刷新令牌。请确保授权时设置了'offline'访问类型。");
                }

                // 使用凭据进行API调用...
                // 例如：
                // Calendar service = new Calendar.Builder(HTTP_TRANSPORT, JSON_FACTORY, credential)
                //     .setApplicationName(APPLICATION_NAME)
                //     .build();
                // EventList events = service.events().list("primary").execute();
                // System.out.println("Upcoming events: " + events.getItems().size());

            } else {
                System.out.println("未能获取到Google访问令牌。");
            }
        } catch (IOException | GeneralSecurityException e) {
            System.err.println("授权过程中发生错误: " + e.getMessage());
            e.printStackTrace();
        }
    }
}