如何在Android Studio中使用Gmail API？

1. Google Cloud平台前期配置 #

• 登录Google Cloud控制台，创建新项目
• 搜索并启用Gmail API
• 创建OAuth 2.0客户端ID：选择「安卓应用」类型，填写你的应用包名和SHA-1指纹（Android Studio可通过Gradle -> Tasks -> android -> signingReport获取指纹）
• 下载生成的google-services.json文件，放到安卓项目的app目录下

2. 项目依赖配置 #

在Module级别的app/build.gradle的dependencies块中添加以下依赖：

implementation 'com.google.android.gms:play-services-auth:20.7.0'
implementation 'com.google.apis:google-api-services-gmail:v1-rev20240105-2.0.0'
implementation 'com.google.oauth-client:google-oauth-client-android:1.34.1'

同步Gradle完成依赖下载

3. 实现OAuth授权流程 #

授权工具类 #

创建GmailAuthHelper类处理账号登录和授权逻辑：

import android.content.Context;
import com.google.android.gms.auth.api.signin.GoogleSignIn;
import com.google.android.gms.auth.api.signin.GoogleSignInAccount;
import com.google.android.gms.auth.api.signin.GoogleSignInClient;
import com.google.android.gms.auth.api.signin.GoogleSignInOptions;
import com.google.android.gms.common.api.Scope;
import com.google.api.services.gmail.GmailScopes;

public class GmailAuthHelper {
    public static final String[] GMAIL_SCOPES = {GmailScopes.GMAIL_READONLY, GmailScopes.GMAIL_SEND};
    
    public static GoogleSignInClient getSignInClient(Context context) {
        GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                .requestScopes(new Scope(GmailScopes.GMAIL_READONLY))
                .requestScopes(new Scope(GmailScopes.GMAIL_SEND))
                .requestEmail()
                .build();
        return GoogleSignIn.getClient(context, gso);
    }
    
    public static boolean isSignedIn(Context context) {
        GoogleSignInAccount account = GoogleSignIn.getLastSignedInAccount(context);
        return account != null;
    }
}

Activity中处理登录请求 #

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;
import com.google.android.gms.auth.api.signin.GoogleSignIn;
import com.google.android.gms.auth.api.signin.GoogleSignInAccount;
import com.google.android.gms.auth.api.signin.GoogleSignInClient;
import com.google.android.gms.common.api.ApiException;
import com.google.android.gms.tasks.Task;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import android.util.Log;

public class MainActivity extends AppCompatActivity {
    private static final int RC_SIGN_IN = 1001;
    private GoogleSignInClient mSignInClient;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mSignInClient = GmailAuthHelper.getSignInClient(this);
        
        findViewById(R.id.btn_sign_in).setOnClickListener(v -> signIn());
    }

    private void signIn() {
        Intent signInIntent = mSignInClient.getSignInIntent();
        startActivityForResult(signInIntent, RC_SIGN_IN);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == RC_SIGN_IN) {
            Task<GoogleSignInAccount> task = GoogleSignIn.getSignedInAccountFromIntent(data);
            handleSignInResult(task);
        }
    }

    private void handleSignInResult(Task<GoogleSignInAccount> completedTask) {
        try {
            GoogleSignInAccount account = completedTask.getResult(ApiException.class);
            // 授权成功，调用Gmail API获取数据
            fetchGmailMessages(account);
        } catch (ApiException e) {
            Log.w("GmailAuth", "登录失败，错误码：" + e.getStatusCode());
        }
    }
}

4. 调用Gmail API获取邮件数据 #

在MainActivity中添加获取收件箱邮件的方法：

import com.google.api.client.extensions.android.http.AndroidHttp;
import com.google.api.client.json.jackson2.JacksonFactory;
import com.google.api.services.gmail.Gmail;
import com.google.api.services.gmail.model.ListMessagesResponse;
import com.google.api.services.gmail.model.Message;
import com.google.api.client.googleapis.extensions.android.gms.auth.GoogleAccountCredential;
import java.io.IOException;

private void fetchGmailMessages(GoogleSignInAccount account) {
    new AsyncTask<Void, Void, List<String>>() {
        @Override
        protected List<String> doInBackground(Void... voids) {
            List<String> messageTitles = new ArrayList<>();
            try {
                GoogleAccountCredential credential = GoogleAccountCredential.usingOAuth2(
                        getApplicationContext(), Arrays.asList(GmailAuthHelper.GMAIL_SCOPES))
                        .setSelectedAccount(account.getAccount());
                
                Gmail gmailService = new Gmail.Builder(AndroidHttp.newCompatibleTransport(), 
                        JacksonFactory.getDefaultInstance(), credential)
                        .setApplicationName("你的应用名称")
                        .build();
                
                // 获取收件箱前10封邮件的标题
                ListMessagesResponse response = gmailService.users().messages().list("me")
                        .setLabelIds(Collections.singletonList("INBOX"))
                        .setMaxResults(10L)
                        .execute();
                
                if (response.getMessages() != null) {
                    for (Message message : response.getMessages()) {
                        Message fullMessage = gmailService.users().messages().get("me", message.getId())
                                .setFormat("METADATA")
                                .setMetadataHeaders(Collections.singletonList("Subject"))
                                .execute();
                        String subject = fullMessage.getPayload().getHeaders().get(0).getValue();
                        messageTitles.add(subject);
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
            return messageTitles;
        }
        
        @Override
        protected void onPostExecute(List<String> messageTitles) {
            // 更新UI展示邮件标题
            StringBuilder sb = new StringBuilder();
            for (String title : messageTitles) {
                sb.append(title).append("\n");
            }
            ((TextView) findViewById(R.id.tv_messages)).setText(sb.toString());
        }
    }.execute();
}

5. 关键注意事项 #

• 网络权限：在AndroidManifest.xml中添加<uses-permission android:name="android.permission.INTERNET" />
• 权限范围：根据实际需求申请Scope，避免申请多余权限（比如仅需读邮件就不要申请发送权限）
• 线程处理：所有Gmail API调用必须在子线程执行，示例中用了AsyncTask，也可替换为Coroutines或RxJava
• 测试验证：确保Cloud控制台配置的SHA-1指纹和包名与本地项目完全一致，使用真实Google账号测试

内容的提问来源于stack exchange，提问作者Riiko