How to use sync token on Google People API - google-people-api

Question

I cannot really find an example on how to use this.
Right now, I'm doing like this:
// Request 10 connections.
ListConnectionsResponse response = peopleService.people().connections()
.list("people/me")
.setRequestSyncToken(true)
.setPageSize(10)
.setPersonFields("names,emailAddresses")
.execute();
I make some changes to my contacts (adding, removing, updating), then I do this:
// Request 10 connections.
ListConnectionsResponse response2 = peopleService.people().connections()
.list("people/me")
.setSyncToken(response.getNextSyncToken())
.setPageSize(10)
.setPersonFields("names,emailAddresses")
.execute();
But it seems like I cannot get the changes I've done earlier, not even if I do them directly from the UI. I'm pretty sure I'm using the sync token in the wrong way.
Update (19/02/2020): In this example I call the API requesting the sync token in the first request (I successfully get the contacts), pause the execution (by breakpoint), delete a contact and update another one (from the web page), resume the execution and then I call the API again with the sync token that I extracted from the previous call. The result is that no change was made for some reason:
// Build a new authorized API client service.
final NetHttpTransport HTTP_TRANSPORT = GoogleNetHttpTransport.newTrustedTransport();
PeopleService peopleService = new PeopleService.Builder(HTTP_TRANSPORT, JSON_FACTORY, getCredentials(HTTP_TRANSPORT))
.setApplicationName(APPLICATION_NAME)
.build();
// Request 10 connections.
ListConnectionsResponse response = peopleService.people().connections()
.list("people/me")
.setPageSize(10)
.setPersonFields("names,emailAddresses")
.setRequestSyncToken(true)
.execute();
// Print display name of connections if available.
List<Person> connections = response.getConnections();
if (connections != null && connections.size() > 0) {
for (Person person : connections) {
List<Name> names = person.getNames();
if (names != null && names.size() > 0) {
System.out.println("Name: " + person.getNames().get(0)
.getDisplayName());
} else {
System.out.println("No names available for connection.");
}
}
} else {
System.out.println("No connections found.");
}
// CORRECT: 2 CONTACTS PRINTED
// CORRECT: THE SYNC TOKEN IS THERE
String syncToken = response.getNextSyncToken();
System.out.println("syncToken = "+syncToken);
// I SETUP A BREAKPOINT BELOW, I DELETE ONE CONTACT AND EDIT ANOTHER AND THEN I RESUME THE EXECUTING
// Request 10 connections.
response = peopleService.people().connections()
.list("people/me")
.setPageSize(10)
.setPersonFields("names,emailAddresses")
.setSyncToken(syncToken)
.execute();
// Print display name of connections if available.
connections = response.getConnections();
if (connections != null && connections.size() > 0) {
for (Person person : connections) {
List<Name> names = person.getNames();
if (names != null && names.size() > 0) {
System.out.println("Name: " + person.getNames().get(0)
.getDisplayName());
} else {
System.out.println("No names available for connection.");
}
}
} else {
System.out.println("No connections found.");
}
// WRONG: I GET "NO CONNECTIONS FOUND"

Answer 1

Something I've found out is that, when requesting or setting a sync token, you must iterate the entirety of the contacts for the nextSyncToken to be populated.
That means that as long as there is a nextPageToken (wink wink setPageSize(10)), the sync token will not be populated.
You could either:
A) Loop over all the contacts using your current
pagination, doing whatever you need to do at every
iteration, and after the last call retrieve the populated
sync token.
B) Iterate over all the contacts in one go, using the max
page size of 2000 and a single personField, retrieve the
token, and then do whatever you need to do. Note that if
you are expecting a user to have more than 2000
contacts, you will still need to call the next pages using
the nextPageToken.
Here is an exemple of a sync loop, adapted from Synchronize Resources Efficiently. Note that I usually use the Python client, so this Java code might not be 100% error free:
private static void run() throws IOException {
Request request = people_service.people().connections()
.list("people/me")
.setPageSize(10)
.setPersonFields("names,emailAddresses");
// Load the sync token stored from the last execution, if any.
// The syncSettingsDataStore is whatever you use for storage.
String syncToken = syncSettingsDataStore.get(SYNC_TOKEN_KEY);
String syncType = null;
// Perform the appropiate sync
if (syncToken == null) {
// Perform a full sync
request.setRequestSyncToken(true);
syncType = "FULL";
} else {
// Try to perform an incremental sync.
request.setSyncToken(syncToken);
syncType = "INCREMENTAL";
}
String pageToken = null;
ListConnectionsResponse response = null;
List<Person> contacts = null;
// Iterate over all the contacts, page by page.
do {
request.setPageToken(pageToken);
try {
response = request.execute();
} catch (GoogleJsonResponseException e) {
if (e.getStatusCode() == 410) {
// A 410 status code, "Gone", indicates that the sync token is
// invalid/expired.
// WARNING: The code is 400 in the Python client. I think the
// Java client uses the correct code, but be on the lookout.
// Clear the sync token.
syncSettingsDataStore.delete(SYNC_TOKEN_KEY);
// And anything else you need before re-syncing.
dataStore.clear();
// Restart
run();
} else {
throw e;
}
}
contacts = response.getItems();
if (contacts.size() == 0) {
System.out.println("No contacts to sync.");
} else if (syncType == "FULL"){
//do full sync for this page.
} else if (syncType == "INCREMENTAL") {
//do incremental sync for this page.
} else {
// What are you doing here???
}
pageToken = response.getNextPageToken();
} while (pageToken != null);
// Store the sync token from the last request for use at the next execution.
syncSettingsDataStore.set(SYNC_TOKEN_KEY, response.getNextSyncToken());
System.out.println("Sync complete.");
}