在java中获取谷歌的电子邮件/用户名？

在Java中获取谷歌的电子邮件/用户名，通常是通过OAuth2.0认证过程来实现的。OAuth2.0是一种授权框架，允许用户在不提供用户名和密码的情况下授权第三方应用访问他们的谷歌账户信息。

以下是使用Google OAuth2.0 API获取用户电子邮件/用户名的步骤：

首先，您需要在Google API控制台创建一个项目，并启用Google+ API和OAuth2.0 API。
创建凭证：在Google API控制台中，创建一个OAuth2.0客户端ID，以便您的应用程序可以访问谷歌账户信息。
安装Google API客户端库：您可以使用Google提供的Java库来简化与Google API的交互。您可以使用Maven或Gradle将其添加到您的项目中。
编写代码：使用Google API Java客户端库，您可以编写以下代码来获取用户的电子邮件/用户名：

import com.google.api.client.auth.oauth2.AuthorizationCodeFlow;
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.jackson2.JacksonFactory;
import com.google.api.client.util.store.FileDataStoreFactory;
import com.google.api.services.plus.Plus;
import com.google.api.services.plus.model.Person;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.security.GeneralSecurityException;
import java.util.Collections;

public class GoogleEmailExample {

    private static final String APPLICATION_NAME = "Google Email Example";
    private static final JsonFactory JSON_FACTORY = JacksonFactory.getDefaultInstance();
    private static final String TOKENS_DIRECTORY_PATH = "tokens";

    private static final List<String> SCOPES = Collections.singletonList("https://www.googleapis.com/auth/plus.me");
    private static final String CREDENTIALS_FILE_PATH = "/path/to/your/credentials.json";

    public static void main(String[] args) throws IOException, GeneralSecurityException {
        // Load client secrets.
        InputStream in = new FileInputStream(CREDENTIALS_FILE_PATH);
        GoogleClientSecrets clientSecrets = GoogleClientSecrets.load(JSON_FACTORY, new InputStreamReader(in));

        // Build flow and trigger user authorization request.
        NetHttpTransport httpTransport = GoogleNetHttpTransport.newTrustedTransport();
        FileDataStoreFactory dataStoreFactory = new FileDataStoreFactory(new File(TOKENS_DIRECTORY_PATH));
        AuthorizationCodeFlow flow = new GoogleAuthorizationCodeFlow.Builder(httpTransport, JSON_FACTORY, clientSecrets, SCOPES)
                .setDataStoreFactory(dataStoreFactory)
                .build();
        Credential credential = new AuthorizationCodeInstalledApp(flow, new LocalServerReceiver()).authorize("user");

        // Build Plus service and get user's email.
        Plus plusService = new Plus.Builder(httpTransport, JSON_FACTORY, credential)
                .setApplicationName(APPLICATION_NAME)
                .build();
        Person person = plusService.people().get("me").execute();
        String email = person.getEmails().get(0).getValue();
        System.out.println("User's email: " + email);
    }
}