با مجموعهها، منظم بمانید
ذخیره و طبقهبندی محتوا براساس اولویتهای شما.
هر منبع دارای یک فیلد نسخه است که هر بار که منبع تغییر می کند تغییر می کند - فیلد etag . تگ ها بخشی استاندارد از HTTP هستند و در API تقویم برای دو مورد پشتیبانی می شوند:
در مورد اصلاحات منبع برای اطمینان از اینکه در این مدت هیچ نوشته دیگری در این منبع وجود نداشته است (اصلاح مشروط)
در بازیابی منبع برای بازیابی اطلاعات منبع فقط در صورتی که منبع تغییر کرده باشد (بازیابی مشروط)
اصلاح مشروط
اگر میخواهید منبعی را فقط در صورتی بهروزرسانی یا حذف کنید که از آخرین باری که آن را بازیابی کردهاید تغییری نکرده باشد، میتوانید یک سرصفحه If-Match را مشخص کنید که حاوی مقدار تگ از بازیابی قبلی باشد. این برای جلوگیری از تغییرات از دست رفته در منابع بسیار مفید است. مشتریان این گزینه را دارند که منبع را دوباره بازیابی کنند و تغییرات را دوباره اعمال کنند.
اگر ورودی (و برچسب آن) از آخرین بازیابی تغییر نکرده باشد، اصلاح با موفقیت انجام می شود و نسخه جدید منبع با برچسب جدید برگردانده می شود. در غیر این صورت، کد پاسخ 412 (پیش شرط ناموفق) را دریافت خواهید کرد.
privatestaticvoidrun()throwsIOException{// Create a test event.Eventevent=Utils.createTestEvent(client,"Test Event");System.out.println(String.format("Event created: %s",event.getHtmlLink()));// Pause while the user modifies the event in the Calendar UI.System.out.println("Modify the event's description and hit enter to continue.");System.in.read();// Modify the local copy of the event.event.setSummary("Updated Test Event");// Update the event, making sure that we don't overwrite other changes.intnumAttempts=0;booleanisUpdated=false;do{Calendar.Events.Updaterequest=client.events().update("primary",event.getId(),event);request.setRequestHeaders(newHttpHeaders().setIfMatch(event.getEtag()));try{event=request.execute();isUpdated=true;}catch(GoogleJsonResponseExceptione){if(e.getStatusCode()==412){// A 412 status code, "Precondition failed", indicates that the etag values didn't// match, and the event was updated on the server since we last retrieved it. Use// {@link Calendar.Events.Get} to retrieve the latest version.EventlatestEvent=client.events().get("primary",event.getId()).execute();// You may want to have more complex logic here to resolve conflicts. In this sample we're// simply overwriting the summary.latestEvent.setSummary(event.getSummary());event=latestEvent;}else{throwe;}}numAttempts++;}while(!isUpdated && numAttempts<=MAX_UPDATE_ATTEMPTS);if(isUpdated){System.out.println("Event updated.");}else{System.out.println(String.format("Failed to update event after %d attempts.",numAttempts));}}
اگر میخواهید یک منبع را فقط در صورتی بازیابی کنید که از آخرین بازیابی شما تغییر کرده باشد، میتوانید یک سرصفحه If-None-Match که حاوی مقدار تگ از بازیابی قبلی است را مشخص کنید. اگر ورودی (و بنابراین برچسب آن) از آخرین بازیابی تغییر کرده باشد، نسخه جدید منبع با برچسب جدید برگردانده می شود. در غیر این صورت کد پاسخ 304 (عدم اصلاح) را دریافت خواهید کرد.
privatestaticvoidrun()throwsIOException{// Create a test event.Eventevent=Utils.createTestEvent(client,"Test Event");System.out.println(String.format("Event created: %s",event.getHtmlLink()));// Pause while the user modifies the event in the Calendar UI.System.out.println("Modify the event's description and hit enter to continue.");System.in.read();// Fetch the event again if it's been modified.Calendar.Events.GetgetRequest=client.events().get("primary",event.getId());getRequest.setRequestHeaders(newHttpHeaders().setIfNoneMatch(event.getEtag()));try{event=getRequest.execute();System.out.println("The event was modified, retrieved latest version.");}catch(GoogleJsonResponseExceptione){if(e.getStatusCode()==304){// A 304 status code, "Not modified", indicates that the etags match, and the event has// not been modified since we last retrieved it.System.out.println("The event was not modified, using local version.");}else{throwe;}}}
تاریخ آخرین بهروزرسانی 2025-08-29 بهوقت ساعت هماهنگ جهانی.
[null,null,["تاریخ آخرین بهروزرسانی 2025-08-29 بهوقت ساعت هماهنگ جهانی."],[],[],null,["# Get specific versions of resources\n\nEvery resource has a version field that changes every time the resource\nchanges --- the `etag` field. Etags are a standard part of HTTP and are\nsupported in the calendar API for two cases:\n\n- on resource modifications to ensure that there has been no other write to this resource in the meantime (conditional modification)\n- on resource retrieval to only retrieve resource data if the resource has changed (conditional retrieval)\n\nConditional modification\n------------------------\n\nIf you want to update or delete a resource only if it has not changed since\nyou last retrieved it, you can specify an `If-Match` header that contains the\nvalue of the etag from the previous retrieval. This is very useful to prevent\nlost modifications on resources. The clients have the option of re-retrieving\nthe resource and re-applying the changes.\n\nIf the entry (and its etag) has not changed since the last retrieval, the\nmodification succeeds and the new version of the resource with the new etag is\nreturned. Otherwise, you will get a 412 (Precondition failed) response code.\n| **Important:** There is no support for conditional modifications for insert operations. Instead, it is guaranteed that if you are allowed to provide a resource ID, then the operation will only succeed if no existing entry has that ID.\n\nThe snippet of sample code below demonstrates how to perform conditional\nmodifications with the\n[Java client library](/api-client-library/java/apis/calendar/v3). \n\n```java\n private static void run() throws IOException {\n // Create a test event.\n Event event = Utils.createTestEvent(client, \"Test Event\");\n System.out.println(String.format(\"Event created: %s\", event.getHtmlLink()));\n\n // Pause while the user modifies the event in the Calendar UI.\n System.out.println(\"Modify the event's description and hit enter to continue.\");\n System.in.read();\n\n // Modify the local copy of the event.\n event.setSummary(\"Updated Test Event\");\n\n // Update the event, making sure that we don't overwrite other changes.\n int numAttempts = 0;\n boolean isUpdated = false;\n do {\n Calendar.Events.Update request = client.events().update(\"primary\", event.getId(), event);\n request.setRequestHeaders(new HttpHeaders().setIfMatch(event.getEtag()));\n try {\n event = request.execute();\n isUpdated = true;\n } catch (GoogleJsonResponseException e) {\n if (e.getStatusCode() == 412) {\n // A 412 status code, \"Precondition failed\", indicates that the etag values didn't\n // match, and the event was updated on the server since we last retrieved it. Use\n // {@link Calendar.Events.Get} to retrieve the latest version.\n Event latestEvent = client.events().get(\"primary\", event.getId()).execute();\n\n // You may want to have more complex logic here to resolve conflicts. In this sample we're\n // simply overwriting the summary.\n latestEvent.setSummary(event.getSummary());\n event = latestEvent;\n } else {\n throw e;\n }\n }\n numAttempts++;\n } while (!isUpdated && numAttempts \u003c= MAX_UPDATE_ATTEMPTS);\n\n if (isUpdated) {\n System.out.println(\"Event updated.\");\n } else {\n System.out.println(String.format(\"Failed to update event after %d attempts.\", numAttempts));\n }\n }https://github.com/googleworkspace/java-samples/blob/26cb124371d51cb5cb8e6c4a3db6422bbef586fb/calendar/sync/src/main/java/com/google/api/services/samples/calendar/sync/ConditionalModificationSample.java\n```\n\nConditional retrieval\n---------------------\n\nIf you want to retrieve a resource only if it has changed since you last\nretrieved it, you can specify an `If-None-Match` header which contains the\nvalue of the etag from the previous retrieval. If the entry (and thus its etag)\nhas changed since the last retrieval, the new version of the resource with the\nnew etag will be returned. Otherwise you will get a 304 (Not Modified)\nresponse code.\n| **Note:** There are special cases in which etags won't change, such as when one of the read-only fields of a `calendarList` entry changes (e.g., calendar properties or ACLs).\n\nThe snippet of sample code below demonstrates how to perform conditional\nretrieval with the\n[Java client library](/api-client-library/java/apis/calendar/v3). \n\n```java\n private static void run() throws IOException {\n // Create a test event.\n Event event = Utils.createTestEvent(client, \"Test Event\");\n System.out.println(String.format(\"Event created: %s\", event.getHtmlLink()));\n\n // Pause while the user modifies the event in the Calendar UI.\n System.out.println(\"Modify the event's description and hit enter to continue.\");\n System.in.read();\n\n // Fetch the event again if it's been modified.\n Calendar.Events.Get getRequest = client.events().get(\"primary\", event.getId());\n getRequest.setRequestHeaders(new HttpHeaders().setIfNoneMatch(event.getEtag()));\n try {\n event = getRequest.execute();\n System.out.println(\"The event was modified, retrieved latest version.\");\n } catch (GoogleJsonResponseException e) {\n if (e.getStatusCode() == 304) {\n // A 304 status code, \"Not modified\", indicates that the etags match, and the event has\n // not been modified since we last retrieved it.\n System.out.println(\"The event was not modified, using local version.\");\n } else {\n throw e;\n }\n }\n }https://github.com/googleworkspace/java-samples/blob/26cb124371d51cb5cb8e6c4a3db6422bbef586fb/calendar/sync/src/main/java/com/google/api/services/samples/calendar/sync/ConditionalRetrievalSample.java\n```"]]