Sure, here's an outline of the steps and sample Java code to get authorization from a user to access their Gmail account using the Google API:

1. Create a new Google Cloud Platform (GCP) project in the Google Cloud Console and enable the Gmail API. You can follow the instructions in this Google documentation: <https://developers.google.com/gmail/api/quickstart/java>
2. Obtain the necessary credentials to authorize your app. You can do this by creating a new OAuth client ID in the GCP console. Choose "Desktop App" as the application type and enter a name for your client ID. Note the client ID and client secret, as you will need them in your Java code.
3. Use the Google API client library for Java to create an authorization request URL and prompt the user to grant your app access to their Gmail account. You can use the following code:
```java
import com.google.api.client.auth.oauth2.AuthorizationCodeFlow;
import com.google.api.client.auth.oauth2.AuthorizationCodeFlow.Builder;
import com.google.api.client.auth.oauth2.AuthorizationCodeRequestUrl;
import com.google.api.client.auth.oauth2.Credential;
import com.google.api.client.auth.oauth2.TokenResponse;
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 com.google.api.services.gmail.GmailScopes;

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

public class GmailAuth {

    private static final String APPLICATION_NAME = "Your app name";
    private static final JsonFactory JSON_FACTORY = JacksonFactory.getDefaultInstance();
    private static final List<String> SCOPES = Arrays.asList(GmailScopes.GMAIL_READONLY, GmailScopes.GMAIL_LABELS);

    private static Credential authorize() throws IOException, GeneralSecurityException {
        HttpTransport httpTransport = GoogleNetHttpTransport.newTrustedTransport();
        File dataStoreDir = new File(System.getProperty("user.home"), ".credentials/" + APPLICATION_NAME);
        FileDataStoreFactory dataStoreFactory = new FileDataStoreFactory(dataStoreDir);

        GoogleClientSecrets clientSecrets = GoogleClientSecrets.load(JSON_FACTORY, new InputStreamReader(GmailAuth.class.getResourceAsStream("/client_secret.json")));

        Builder flowBuilder = new GoogleAuthorizationCodeFlow.Builder(httpTransport, JSON_FACTORY, clientSecrets, SCOPES);
        AuthorizationCodeFlow flow = flowBuilder.setDataStoreFactory(dataStoreFactory).build();

        Credential credential = new AuthorizationCodeInstalledApp(flow, new LocalServerReceiver()).authorize("user");
        System.out.println("Credentials saved to " + dataStoreDir.getAbsolutePath());
        return credential;
    }

    public static void main(String[] args) throws IOException, GeneralSecurityException {
        authorize();
    }

}
```
4. After the user grants access to your app, the authorization server will redirect the user's browser to the redirect URI you specified in the GCP console, with an authorization code included in the query string. Your app can then exchange this authorization code for an access token using the Google API client library for Java. You can use the following code:
```java
import com.google.api.client.auth.oauth2.Credential;
import com.google.api.client.auth.oauth2.TokenResponse;
import com.google.api.client.googleapis.auth.oauth2
```
다음은 Google API를 사용하여 사용자가 Gmail 계정에 액세스할 수 있도록 권한을 부여하는 단계와 샘플 Java 코드에 대한 개요입니다:

1. Google 클라우드 콘솔에서 새 Google 클라우드 플랫폼(GCP) 프로젝트를 생성하고 Gmail API를 사용 설정합니다. 이 Google 설명서의 지침을 따를 수 있습니다: <https://developers.google.com/gmail/api/quickstart/java>
2. 앱을 인증하는 데 필요한 자격 증명을 얻습니다. GCP 콘솔에서 새 OAuth 클라이언트 ID를 생성하여 이를 수행할 수 있습니다. 애플리케이션 유형으로 "데스크톱 앱"을 선택하고 클라이언트 ID의 이름을 입력합니다. 클라이언트 ID와 클라이언트 비밀 번호는 Java 코드에 필요하므로 메모해 두세요.
3. 3. Java용 Google API 클라이언트 라이브러리를 사용하여 인증 요청 URL을 생성하고 사용자에게 앱의 Gmail 계정 액세스 권한을 부여하라는 메시지를 표시합니다. 다음 코드를 사용할 수 있습니다:
```java
import com.google.api.client.auth.oauth2.AuthorizationCodeFlow;
import com.google.api.client.auth.oauth2.AuthorizationCodeFlow.Builder;
com.google.api.client.auth.oauth2.AuthorizationCodeRequestUrl을 가져옵니다;
com.google.api.client.auth.oauth2.Credential을 가져옵니다;
com.google.api.client.auth.oauth2.TokenResponse를 가져옵니다;
com.google.api.client.extensions.java6.auth.oauth2.AuthorizationCodeInstalledApp를 가져옵니다;
com.google.api.client.extensions.jetty.auth.oauth2.LocalServerReceiver를 가져옵니다;
com.google.api.client.googleapis.auth.oauth2.GoogleAuthorizationCodeFlow를 가져옵니다;
import com.google.api.client.googleapis.auth.oauth2.GoogleClientSecrets;
import com.google.api.client.googleapis.javanet.GoogleNetHttpTransport;
com.google.api.client.http.HttpTransport를 가져옵니다;
com.google.api.client.json.JsonFactory를 가져옵니다;
import com.google.api.client.json.jackson2.JacksonFactory;
com.google.api.client.util.store.FileDataStoreFactory를 가져옵니다;
com.google.api.services.gmail.GmailScopes를 가져옵니다;

java.io.File을 가져옵니다;
java.io.IOException을 임포트합니다;
java.io.InputStreamReader를 임포트합니다;
java.security.GeneralSecurityException;
import java.util.Arrays;
java.util.List를 가져옵니다;

public class GmailAuth {

    private static final String APPLICATION_NAME = "귀하의 앱 이름";
    private static final JsonFactory JSON_FACTORY = JacksonFactory.getDefaultInstance();
    private static final List<String> SCOPES = Arrays.asList(GmailScopes.GMAIL_READONLY, GmailScopes.GMAIL_LABELS);

    비공개 정적 Credential authorize() throws IOException, GeneralSecurityException {
        HttpTransport httpTransport = GoogleNetHttpTransport.newTrustedTransport();
        파일 dataStoreDir = 새 파일(System.getProperty("user.home"), ".credentials/" + APPLICATION_NAME);
        파일데이터저장소 데이터저장소 = 새로운 파일데이터저장소(데이터저장소Dir);

        GoogleClientSecrets clientSecrets = GoogleClientSecrets.load(JSON_FACTORY, new InputStreamReader(GmailAuth.class.getResourceAsStream("/client_secret.json")));

        빌더 flowBuilder = 새로운 GoogleAuthorizationCodeFlow.Builder(httpTransport, JSON_FACTORY, clientSecrets, SCOPES);
        권한부여코드흐름 flow = flowBuilder.setDataStoreFactory(dataStoreFactory).build();

        자격 증명 자격 증명 = 새 AuthorizationCodeInstalledApp(흐름, 새 LocalServerReceiver()).authorize("사용자");
        System.out.println("자격 증명이 다음에 저장되었습니다." + dataStoreDir.getAbsolutePath());
        자격 증명을 반환합니다;
    }

    public static void main(String[] args) throws IOException, GeneralSecurityException {
        authorize();
    }

}
```
4. 사용자가 앱에 대한 액세스 권한을 부여하면 권한 부여 서버는 쿼리 문자열에 포함된 권한 부여 코드와 함께 사용자의 브라우저를 GCP 콘솔에서 지정한 리디렉션 URI로 리디렉션합니다. 그런 다음 앱에서 Java용 Google API 클라이언트 라이브러리를 사용하여 이 인증 코드를 액세스 토큰으로 교환할 수 있습니다. 다음 코드를 사용할 수 있습니다:
```java
import com.google.api.client.auth.oauth2.Credential;
import com.google.api.client.auth.oauth2.TokenResponse;
import com.google.api.client.googleapis.auth.oauth2
```