Java 应用中获取 Google OAuth 2.0 访问令牌的实用指南

<dependencies>
    <!-- Google API 客户端核心库 -->
    <dependency>
        <groupId>com.google.api-client</groupId>
        <artifactId>google-api-client</artifactId>
        <version>1.32.1</version> <!-- 推荐使用最新稳定版本 -->
    </dependency>

    <!-- Google OAuth 客户端库 -->
    <dependency>
        <groupId>com.google.oauth-client</groupId>
        <artifactId>google-oauth-client</artifactId>
        <version>1.32.1</version>
    </dependency>

    <!-- Google OAuth 客户端库，用于 Jetty 服务器（桌面应用授权回调） -->
    <dependency>
        <groupId>com.google.oauth-client</groupId>
        <artifactId>google-oauth-client-jetty</artifactId>
        <version>1.32.1</version>
    </dependency>

    <!-- Google HTTP 客户端库，用于 Jackson2 JSON 解析 -->
    <dependency>
        <groupId>com.google.http-client</groupId>
        <artifactId>google-http-client-jackson2</artifactId>
        <version>1.39.2</version>
    </dependency>

    <!-- Google OAuth 客户端库，用于 Java 6+ (包含 FileDataStoreFactory 等) -->
    <dependency>
        <groupId>com.google.oauth-client</groupId>
        <artifactId>google-oauth-client-java6</artifactId>
        <version>1.32.1</version>
    </dependency>
</dependencies>

{
  "web": { // 如果您选择的是“Web 应用”类型，这里是 "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" // 或其他配置的重定向 URI
    ]
  },
  "installed": { // 如果您选择的是“桌面应用”类型，这里是 "installed"
    "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"
    ]
  }
}

package com.example.googleauth;

import com.google.api.client.auth.oauth2.Credential;
import com.google.api.client.extensions.java6.auth.oauth2.FileDataStoreFactory;
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.DataStoreFactory;
import com.google.api.client.extensions.java6.auth.oauth2.AuthorizationCodeInstalledApp;

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 GoogleTokenFetcher {

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

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

    /** HTTP 传输器 */
    private static HttpTransport HTTP_TRANSPORT;

    /** 数据存储工厂，用于持久化凭据（如刷新令牌） */
    private static FileDataStoreFactory DATA_STORE_FACTORY;

    /**
     * 定义应用程序所需的授权范围（Scopes）。
     * 这里以访问 Google 日历为例，您可以根据需要更改。
     * 更多 Scope 请参考 Google API 文档。
     */
    private static final List<String> SCOPES = Collections.singletonList("https://www.googleapis.com/auth/calendar.readonly");
    // 如果需要访问用户个人资料，可以使用 "https://www.googleapis.com/auth/userinfo.profile"
    // 或 "https://www.googleapis.com/auth/userinfo.email"
    // 甚至更通用的 "https://www.googleapis.com/auth/drive.readonly" 等

    static {
        try {
            HTTP_TRANSPORT = GoogleNetHttpTransport.newTrustedTransport();
            // 凭据将存储在用户主目录下的 .store/google_token_fetcher 目录中
            DATA_STORE_FACTORY = new FileDataStoreFactory(new File(System.getProperty("user.home"), ".store/google_token_fetcher"));
        } catch (GeneralSecurityException | IOException e) {
            e.printStackTrace();
            System.exit(1);
        }
    }

    public static void main(String[] args) throws IOException {
        try {
            Credential credential = authorize();
            if (credential != null && credential.getAccessToken() != null) {
                String accessToken = credential.getAccessToken();
                System.out.println("成功获取访问令牌 (Access Token): " + accessToken);

                // 您可以使用这个访问令牌调用 Google API
                // 例如：
                // Calendar service = new Calendar.Builder(HTTP_TRANSPORT, JSON_FACTORY, credential)
                //         .setApplicationName(APPLICATION_NAME)
                //         .build();
                // Event event = service.events().get("primary", "eventId").execute();
                // System.out.println("获取到的事件：" + event.getSummary());

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

    /**
     * 授权安装的应用程序访问用户的受保护数据。
     * @return Credential 对象，包含访问令牌和刷新令牌
     * @throws Exception 如果授权过程中发生错误
     */
    private static Credential authorize() throws Exception {
        // 1. 加载客户端密钥 (client_secrets.json)
        // 确保 client_secrets.json 文件在类路径中 (例如 src/main/resources)
        GoogleClientSecrets clientSecrets = GoogleClientSecrets.load(
                JSON_FACTORY,
                new InputStreamReader(GoogleTokenFetcher.class.getResourceAsStream("/client_secrets.json"))
        );

        // 2. 设置授权代码流
        GoogleAuthorizationCodeFlow flow = new GoogleAuthorizationCodeFlow.Builder(
                HTTP_TRANSPORT,
                JSON_FACTORY,
                clientSecrets,
                SCOPES // 应用程序所需的权限范围
            )
            .setDataStoreFactory(DATA_STORE_FACTORY) // 用于持久化凭据，例如刷新令牌
            .setAccessType("offline") // 请求刷新令牌，以便在访问令牌过期后重新获取
            .build();

        // 3. 授权用户
        // LocalServerReceiver 会在本地启动一个服务器，监听 Google 授权回调
        LocalServerReceiver receiver = new LocalServerReceiver.Builder().setPort(8888).build(); // 可以指定端口
        return new AuthorizationCodeInstalledApp(flow, receiver).authorize("user");
    }
}