对于必须跟踪文件更改的 Google 云端硬盘应用，changes 集合提供了一种高效的方式来检测所有文件更改，包括与用户共享的更改。如果文件已更改，该集合会提供每个文件的当前状态。
获取首页令牌
如需请求账号当前状态的页面令牌，请使用 changes.getStartPageToken。在对 changes.list 的初始调用中存储并使用此令牌。
如需检索当前网页令牌，请参考以下代码：
Java
drive/snippets/drive_v3/src/main/java/FetchStartPageToken.java
import com.google.api.client.googleapis.json.GoogleJsonResponseException;
import com.google.api.client.http.HttpRequestInitializer;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.gson.GsonFactory;
import com.google.api.services.drive.Drive;
import com.google.api.services.drive.DriveScopes;
import com.google.api.services.drive.model.StartPageToken;
import com.google.auth.http.HttpCredentialsAdapter;
import com.google.auth.oauth2.GoogleCredentials;
import java.io.IOException;
import java.util.Arrays;
/* Class to demonstrate use-case of Drive's fetch start page token */
public class FetchStartPageToken {
/**
* Retrieve the start page token for the first time.
*
* @return Start page token as String.
* @throws IOException if file is not found
*/
public static String fetchStartPageToken() throws IOException {
/*Load pre-authorized user credentials from the environment.
TODO(developer) - See https://developers.google.com/identity for
guides on implementing OAuth2 for your application. */
GoogleCredentials credentials = GoogleCredentials.getApplicationDefault()
.createScoped(Arrays.asList(DriveScopes.DRIVE_FILE));
HttpRequestInitializer requestInitializer = new HttpCredentialsAdapter(
credentials);
// Build a new authorized API client service.
Drive service = new Drive.Builder(new NetHttpTransport(),
GsonFactory.getDefaultInstance(),
requestInitializer)
.setApplicationName("Drive samples")
.build();
try {
StartPageToken response = service.changes()
.getStartPageToken().execute();
System.out.println("Start token: " + response.getStartPageToken());
return response.getStartPageToken();
} catch (GoogleJsonResponseException e) {
// TODO(developer) - handle error appropriately
System.err.println("Unable to fetch start page token: " + e.getDetails());
throw e;
}
}
}
Python
drive/snippets/drive-v3/change_snippet/fetch_start_page_token.py
import google.auth
from googleapiclient.discovery import build
from googleapiclient.errors import HttpError
def fetch_start_page_token():
"""Retrieve page token for the current state of the account.
Returns & prints : start page token
Load pre-authorized user credentials from the environment.
TODO(developer) - See https://developers.google.com/identity
for guides on implementing OAuth2 for the application.
"""
creds, _ = google.auth.default()
try:
# create drive api client
service = build("drive", "v3", credentials=creds)
# pylint: disable=maybe-no-member
response = service.changes().getStartPageToken().execute()
print(f'Start token: {response.get("startPageToken")}')
except HttpError as error:
print(f"An error occurred: {error}")
response = None
return response.get("startPageToken")
if __name__ == "__main__":
fetch_start_page_token()
PHP
drive/snippets/drive_v3/src/DriveFetchStartPageToken.php
use Google\Client;
use Google\Service\Drive;
# TODO - PHP client currently chokes on fetching start page token
function fetchStartPageToken()
{
try {
$client = new Client();
$client->useApplicationDefaultCredentials();
$client->addScope(Drive::DRIVE);
$driveService = new Drive($client);
$response = $driveService->changes->getStartPageToken();
printf("Start token: %s\n", $response->startPageToken);
return $response->startPageToken;
} catch(Exception $e) {
echo "Error Message: ".$e;
}
}
.NET
drive/snippets/drive_v3/DriveV3Snippets/FetchStartPageToken.cs
using Google.Apis.Auth.OAuth2;
using Google.Apis.Drive.v3;
using Google.Apis.Services;
namespace DriveV3Snippets
{
// Class to demonstrate use-case of Drive's fetch start page token
public class FetchStartPageToken
{
/// <summary>
/// Retrieve the starting page token.
/// </summary>
/// <returns>start page token as String, null otherwise.</returns>
public static string DriveFetchStartPageToken()
{
try
{
/* Load pre-authorized user credentials from the environment.
TODO(developer) - See https://developers.google.com/identity for
guides on implementing OAuth2 for your application. */
GoogleCredential credential = GoogleCredential.GetApplicationDefault()
.CreateScoped(DriveService.Scope.Drive);
// Create Drive API service.
var service = new DriveService(new BaseClientService.Initializer
{
HttpClientInitializer = credential,
ApplicationName = "Drive API Snippets"
});
var response = service.Changes.GetStartPageToken().Execute();
// Prints the token value.
Console.WriteLine("Start token: " + response.StartPageTokenValue);
return response.StartPageTokenValue;
}
catch (Exception e)
{
// TODO(developer) - handle error appropriately
if (e is AggregateException)
{
Console.WriteLine("Credential Not found");
}
else
{
throw;
}
}
return null;
}
}
}
Node.js
drive/snippets/drive_v3/change_snippets/fetch_start_page_token.js
/**
* Retrieve page token for the current state of the account.
**/
async function fetchStartPageToken() {
// Get credentials and build service
// TODO (developer) - Use appropriate auth mechanism for your app
const {GoogleAuth} = require('google-auth-library');
const {google} = require('googleapis');
const auth = new GoogleAuth({
scopes: 'https://www.googleapis.com/auth/drive.appdata',
});
const service = google.drive({version: 'v3', auth});
try {
const res = await service.changes.getStartPageToken({});
const token = res.data.startPageToken;
console.log('start token: ', token);
return token;
} catch (err) {
// TODO(developer) - Handle error
throw err;
}
}
获取更改
如需检索当前已登录用户的更改列表，请向 changes 集合发送 GET 请求，如 changes.list 中所详述。
changes 集合中的条目按时间顺序排列（最早的更改显示在前面）。includeRemoved 和 restrictToMyDrive 查询参数决定了响应中是否应包含已移除或已分享的项目。
Java
drive/snippets/drive_v3/src/main/java/FetchChanges.java
import com.google.api.client.googleapis.json.GoogleJsonResponseException;
import com.google.api.client.http.HttpRequestInitializer;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.gson.GsonFactory;
import com.google.api.services.drive.Drive;
import com.google.api.services.drive.DriveScopes;
import com.google.api.services.drive.model.ChangeList;
import com.google.auth.http.HttpCredentialsAdapter;
import com.google.auth.oauth2.GoogleCredentials;
import java.io.IOException;
import java.util.Arrays;
/* Class to demonstrate use-case of Drive's fetch changes in file. */
public class FetchChanges {
/**
* Retrieve the list of changes for the currently authenticated user.
*
* @param savedStartPageToken Last saved start token for this user.
* @return Saved token after last page.
* @throws IOException if file is not found
*/
public static String fetchChanges(String savedStartPageToken) throws IOException {
/*Load pre-authorized user credentials from the environment.
TODO(developer) - See https://developers.google.com/identity for
guides on implementing OAuth2 for your application.*/
GoogleCredentials credentials = GoogleCredentials.getApplicationDefault()
.createScoped(Arrays.asList(DriveScopes.DRIVE_FILE));
HttpRequestInitializer requestInitializer = new HttpCredentialsAdapter(
credentials);
// Build a new authorized API client service.
Drive service = new Drive.Builder(new NetHttpTransport(),
GsonFactory.getDefaultInstance(),
requestInitializer)
.setApplicationName("Drive samples")
.build();
try {
// Begin with our last saved start token for this user or the
// current token from getStartPageToken()
String pageToken = savedStartPageToken;
while (pageToken != null) {
ChangeList changes = service.changes().list(pageToken)
.execute();
for (com.google.api.services.drive.model.Change change : changes.getChanges()) {
// Process change
System.out.println("Change found for file: " + change.getFileId());
}
if (changes.getNewStartPageToken() != null) {
// Last page, save this token for the next polling interval
savedStartPageToken = changes.getNewStartPageToken();
}
pageToken = changes.getNextPageToken();
}
return savedStartPageToken;
} catch (GoogleJsonResponseException e) {
// TODO(developer) - handle error appropriately
System.err.println("Unable to fetch changes: " + e.getDetails());
throw e;
}
}
}
Python
drive/snippets/drive-v3/change_snippet/fetch_changes.py
import google.auth
from googleapiclient.discovery import build
from googleapiclient.errors import HttpError
def fetch_changes(saved_start_page_token):
"""Retrieve the list of changes for the currently authenticated user.
prints changed file's ID
Args:
saved_start_page_token : StartPageToken for the current state of the
account.
Returns: saved start page token.
Load pre-authorized user credentials from the environment.
TODO(developer) - See https://developers.google.com/identity
for guides on implementing OAuth2 for the application.
"""
creds, _ = google.auth.default()
try:
# create drive api client
service = build("drive", "v3", credentials=creds)
# Begin with our last saved start token for this user or the
# current token from getStartPageToken()
page_token = saved_start_page_token
# pylint: disable=maybe-no-member
while page_token is not None:
response = (
service.changes().list(pageToken=page_token, spaces="drive").execute()
)
for change in response.get("changes"):
# Process change
print(f'Change found for file: {change.get("fileId")}')
if "newStartPageToken" in response:
# Last page, save this token for the next polling interval
saved_start_page_token = response.get("newStartPageToken")
page_token = response.get("nextPageToken")
except HttpError as error:
print(f"An error occurred: {error}")
saved_start_page_token = None
return saved_start_page_token
if __name__ == "__main__":
# saved_start_page_token is the token number
fetch_changes(saved_start_page_token=209)
PHP
drive/snippets/drive_v3/src/DriveFetchChanges.php
use Google\Client;
use Google\Service\Drive;
# TODO - PHP client currently chokes on fetching start page token
function fetchChanges()
{
try {
$client = new Client();
$client->useApplicationDefaultCredentials();
$client->addScope(Drive::DRIVE);
$driveService = new Drive($client);
# Begin with our last saved start token for this user or the
# current token from getStartPageToken()
$savedStartPageToken = readLine("Enter Start Page Token: ");
$pageToken = $savedStartPageToken;
while ($pageToken != null) {
$response = $driveService->changes->listChanges($pageToken, array(
'spaces' => 'drive'
));
foreach ($response->changes as $change) {
// Process change
printf("Change found for file: %s", $change->fileId);
}
if ($response->newStartPageToken != null) {
// Last page, save this token for the next polling interval
$savedStartPageToken = $response->newStartPageToken;
}
$pageToken = $response->nextPageToken;
}
echo $savedStartPageToken;
} catch(Exception $e) {
echo "Error Message: ".$e;
}
}
require_once 'vendor/autoload.php';
.NET
drive/snippets/drive_v3/DriveV3Snippets/FetchChanges.cs
using Google.Apis.Auth.OAuth2;
using Google.Apis.Drive.v3;
using Google.Apis.Services;
namespace DriveV3Snippets
{
// Class to demonstrate use-case of Drive's fetch changes in file.
public class FetchChanges
{
/// <summary>
/// Retrieve the list of changes for the currently authenticated user.
/// prints changed file's ID
/// </summary>
/// <param name="savedStartPageToken">last saved start token for this user.</param>
/// <returns>saved token for the current state of the account, null otherwise.</returns>
public static string DriveFetchChanges(string savedStartPageToken)
{
try
{
/* Load pre-authorized user credentials from the environment.
TODO(developer) - See https://developers.google.com/identity for
guides on implementing OAuth2 for your application. */
GoogleCredential credential = GoogleCredential.GetApplicationDefault()
.CreateScoped(DriveService.Scope.Drive);
// Create Drive API service.
var service = new DriveService(new BaseClientService.Initializer
{
HttpClientInitializer = credential,
ApplicationName = "Drive API Snippets"
});
// Begin with our last saved start token for this user or the
// current token from GetStartPageToken()
string pageToken = savedStartPageToken;
while (pageToken != null)
{
var request = service.Changes.List(pageToken);
request.Spaces = "drive";
var changes = request.Execute();
foreach (var change in changes.Changes)
{
// Process change
Console.WriteLine("Change found for file: " + change.FileId);
}
if (changes.NewStartPageToken != null)
{
// Last page, save this token for the next polling interval
savedStartPageToken = changes.NewStartPageToken;
}
pageToken = changes.NextPageToken;
}
return savedStartPageToken;
}
catch (Exception e)
{
// TODO(developer) - handle error appropriately
if (e is AggregateException)
{
Console.WriteLine("Credential Not found");
}
else
{
throw;
}
}
return null;
}
}
}
Node.js
drive/snippets/drive_v3/change_snippets/fetch_changes.js
/**
* Retrieve the list of changes for the currently authenticated user.
* @param {string} savedStartPageToken page token got after executing fetch_start_page_token.js file
**/
async function fetchChanges(savedStartPageToken) {
// Get credentials and build service
// TODO (developer) - Use appropriate auth mechanism for your app
const {GoogleAuth} = require('google-auth-library');
const {google} = require('googleapis');
const auth = new GoogleAuth({
scopes: 'https://www.googleapis.com/auth/drive.readonly',
});
const service = google.drive({version: 'v3', auth});
try {
let pageToken = savedStartPageToken;
do {
const res = await service.changes.list({
pageToken: savedStartPageToken,
fields: '*',
});
res.data.changes.forEach((change) => {
console.log('change found for file: ', change.fileId);
});
pageToken = res.data.newStartPageToken;
return pageToken;
} while (pageToken);
} catch (err) {
// TODO(developer) - Handle error
throw err;
}
}
响应中的 changes 集合可能包含 nextPageToken。如果列出了 nextPageToken，则可以使用它收集下一页的更改。如果未列出，客户端应用应在响应中存储 newStartPageToken，以供日后使用。存储页面令牌后，客户端应用便可准备好在日后再次查询更改。
接收通知
使用 changes.watch 方法订阅更新日志中的更新。通知不包含更改的详细信息。而是表示有新更改可用。如需检索实际更改，请按照获取更改中所述的方式轮询更改 Feed。
如需了解详情，请参阅资源更改通知。