GoogleCredential.java

HttpTransport httpTransport = GoogleNetHttpTransport.newTrustedTransport();
JsonFactory jsonFactory = JacksonFactory.getDefaultInstance();

// Google Cloud Platform에서 발급 받은 인증서 파일입니다.
InputStream inputStream = getClass().getResourceAsStream(p12FilePath);

// Google Cloud Platform에서 인증서를 발급 받은 서비스 계정명입니다.
GoogleCredential credential = new GoogleCredential.Builder()
        .setTransport(httpTransport)
        .setJsonFactory(jsonFactory)
        .setServiceAccountId(serviceAccountId)
        .setServiceAccountScopes(
                Collections.singleton(AndroidPublisherScopes.ANDROIDPUBLISHER))
        .setServiceAccountPrivateKeyFromP12File(inputStream)
        .build();

credential.refreshToken();

return credential.getAccessToken();