import com.google.api.client.googleapis.compute.ComputeCredential; //导入依赖的package包/类
/**
 * Initializes OAuth2 credential using preconfigured ServiceAccount settings on the local
 * GCE VM. See: <a href="https://developers.google.com/compute/docs/authentication"
 * >Authenticating from Google Compute Engine</a>.
 */
public Credential getCredentialFromMetadataServiceAccount()
    throws IOException, GeneralSecurityException {
  LOG.debug("getCredentialFromMetadataServiceAccount()");
  Credential cred =
      new ComputeCredentialWithRetry(
          new ComputeCredential.Builder(getStaticHttpTransport(), JSON_FACTORY)
              .setRequestInitializer(new CredentialHttpRetryInitializer()));
  try {
    cred.refreshToken();
  } catch (IOException e) {
    throw new IOException("Error getting access token from metadata server at: "
        + ComputeCredential.TOKEN_SERVER_ENCODED_URL, e);
  }
  return cred;
}
 

import com.google.api.client.googleapis.compute.ComputeCredential; //导入依赖的package包/类
/**
 * Initializes OAuth2 credential using preconfigured ServiceAccount settings on the local
 * GCE VM. See: <a href="https://developers.google.com/compute/docs/authentication"
 * >Authenticating from Google Compute Engine</a>.
 */
public static Credentials getCredentialFromMetadataServiceAccount()
    throws IOException, GeneralSecurityException {
  Credentials cred = new ComputeEngineCredentials(getHttpTransport());
  try {
    cred.refresh();
  } catch (IOException e) {
    throw new IOException("Error getting access token from metadata server at: " +
        ComputeCredential.TOKEN_SERVER_ENCODED_URL, e);
  }
  return cred;
}
 

import com.google.api.client.googleapis.compute.ComputeCredential; //导入依赖的package包/类
/**
 * @see http://developers.guge.io/accounts/docs/OAuth2ServiceAccount#creatinganaccount
 * @see https://developers.google.com/accounts/docs/OAuth2
 */
private ComputeCredential getComputeCredential() throws IOException
{
    ComputeCredential credential = new ComputeCredential.Builder(httpTransport, jsonFactory)
            .build();
    credential.refreshToken();

    return credential;
}
 

import com.google.api.client.googleapis.compute.ComputeCredential; //导入依赖的package包/类
/**
 * {@inheritDoc}
 */
@Override
public ComputeCredential getGoogleCredential(
    GoogleOAuth2ScopeRequirement requirement)
    throws GeneralSecurityException {
  // Ideally GCE would allow us to down-scope the metadata credentials we are
  // providing a given library.
  return new ComputeCredential(
      getModule().getHttpTransport(), getModule().getJsonFactory());
}
 

import com.google.api.client.googleapis.compute.ComputeCredential; //导入依赖的package包/类
public synchronized Compute client() {
    if (refreshInterval != null && refreshInterval.millis() != 0) {
        if (client != null &&
            (refreshInterval.millis() < 0 || (System.currentTimeMillis() - lastRefresh) < refreshInterval.millis())) {
            if (logger.isTraceEnabled()) logger.trace("using cache to retrieve client");
            return client;
        }
        lastRefresh = System.currentTimeMillis();
    }

    try {
        gceJsonFactory = new JacksonFactory();

        logger.info("starting GCE discovery service");
        // Forcing Google Token API URL as set in GCE SDK to
        //      http://metadata/computeMetadata/v1/instance/service-accounts/default/token
        // See https://developers.google.com/compute/docs/metadata#metadataserver
        String tokenServerEncodedUrl = GceMetadataService.GCE_HOST.get(settings) +
            "/computeMetadata/v1/instance/service-accounts/default/token";
        ComputeCredential credential = new ComputeCredential.Builder(getGceHttpTransport(), gceJsonFactory)
            .setTokenServerEncodedUrl(tokenServerEncodedUrl)
            .build();

        // hack around code messiness in GCE code
        // TODO: get this fixed
        Access.doPrivilegedIOException(credential::refreshToken);

        logger.debug("token [{}] will expire in [{}] s", credential.getAccessToken(), credential.getExpiresInSeconds());
        if (credential.getExpiresInSeconds() != null) {
            refreshInterval = TimeValue.timeValueSeconds(credential.getExpiresInSeconds() - 1);
        }


        Compute.Builder builder = new Compute.Builder(getGceHttpTransport(), gceJsonFactory, null).setApplicationName(VERSION)
            .setRootUrl(GCE_ROOT_URL.get(settings));

        if (RETRY_SETTING.exists(settings)) {
            TimeValue maxWait = MAX_WAIT_SETTING.get(settings);
            RetryHttpInitializerWrapper retryHttpInitializerWrapper;

            if (maxWait.getMillis() > 0) {
                retryHttpInitializerWrapper = new RetryHttpInitializerWrapper(credential, maxWait);
            } else {
                retryHttpInitializerWrapper = new RetryHttpInitializerWrapper(credential);
            }
            builder.setHttpRequestInitializer(retryHttpInitializerWrapper);

        } else {
            builder.setHttpRequestInitializer(credential);
        }

        this.client = builder.build();
    } catch (Exception e) {
        logger.warn("unable to start GCE discovery service", e);
        throw new IllegalArgumentException("unable to start GCE discovery service", e);
    }

    return this.client;
}
 

import com.google.api.client.googleapis.compute.ComputeCredential; //导入依赖的package包/类
private Credential authorize() throws Exception {
    JsonFactory JSON_FACTORY = JacksonFactory.getDefaultInstance();
    HttpTransport httpTransport = GoogleNetHttpTransport.newTrustedTransport();
    return new ComputeCredential.Builder(httpTransport, JSON_FACTORY).build();
}