如何使用GoogleCredentials创建Gmail服务？解决编译错误

问题背景 #

使用的Maven依赖：

<dependency>
    <groupId>com.google.api-client</groupId>
    <artifactId>google-api-client</artifactId>
    <version>2.7.0</version>
</dependency>
<dependency>
    <groupId>com.google.auth</groupId>
    <artifactId>google-auth-library-oauth2-http</artifactId>
    <version>1.25.0</version>
</dependency>
<dependency>
    <groupId>com.google.apis</groupId>
    <artifactId>google-api-services-gmail</artifactId>
    <version>v1-rev20240520-2.0.0</version>
</dependency>

按照官方文档编写Gmail客户端代码时，采用GoogleCredentials替代已弃用的GoogleCredential，但触发编译错误：GoogleCredentials不属于HttpRequestInitializer类型，原代码如下：

GoogleCredentials credentials = GoogleCredentials.newBuilder()
                .setAccessToken(
                        AccessToken.newBuilder()
                                .setTokenValue(googleTokenResult.getAccessToken())
                                .setExpirationTime(new Date(googleTokenResult.accessTokenExpirationUnixTime))
                                .setScopes(SCOPES)
                                .build()
                )
                .build();
Gmail service = new Gmail.Builder(HTTP_TRANSPORT, JSON_FACTORY, credentials)
                .setApplicationName(APPLICATION_NAME)
                .build();

解决方法 #

GoogleCredentials本身并未实现HttpRequestInitializer接口，需要通过HttpCredentialsAdapter类完成适配——这是Google Auth库提供的专门用于将GoogleCredentials转换为HttpRequestInitializer的工具类。

修改后的代码如下：

import com.google.auth.http.HttpCredentialsAdapter;

// 保留原凭证创建逻辑
GoogleCredentials credentials = GoogleCredentials.newBuilder()
                .setAccessToken(
                        AccessToken.newBuilder()
                                .setTokenValue(googleTokenResult.getAccessToken())
                                .setExpirationTime(new Date(googleTokenResult.accessTokenExpirationUnixTime))
                                .setScopes(SCOPES)
                                .build()
                )
                .build();

// 用HttpCredentialsAdapter包装凭证，转换为HttpRequestInitializer类型
HttpRequestInitializer requestInitializer = new HttpCredentialsAdapter(credentials);

// 创建Gmail服务时传入适配后的实例
Gmail service = new Gmail.Builder(HTTP_TRANSPORT, JSON_FACTORY, requestInitializer)
                .setApplicationName(APPLICATION_NAME)
                .build();

当前使用的google-auth-library-oauth2-http:1.25.0版本已包含HttpCredentialsAdapter，无需额外添加依赖。

内容的提问来源于stack exchange，提问作者HeronAlgoSearch