software.amazon.awssdk.services.dynamodb.paginators.BatchGetItemPublisher Maven / Gradle / Ivy
/*
* Copyright 2013-2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License"). You may not use this file except in compliance with
* the License. A copy of the License is located at
*
* http://aws.amazon.com/apache2.0
*
* or in the "license" file accompanying this file. This file is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
* CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions
* and limitations under the License.
*/
package software.amazon.awssdk.services.dynamodb.paginators;
import java.util.concurrent.CompletableFuture;
import org.reactivestreams.Subscriber;
import software.amazon.awssdk.annotations.Generated;
import software.amazon.awssdk.core.async.SdkPublisher;
import software.amazon.awssdk.core.pagination.async.AsyncPageFetcher;
import software.amazon.awssdk.core.pagination.async.EmptySubscription;
import software.amazon.awssdk.core.pagination.async.ResponsesSubscription;
import software.amazon.awssdk.core.util.SdkAutoConstructList;
import software.amazon.awssdk.core.util.SdkAutoConstructMap;
import software.amazon.awssdk.services.dynamodb.DynamoDbAsyncClient;
import software.amazon.awssdk.services.dynamodb.model.BatchGetItemRequest;
import software.amazon.awssdk.services.dynamodb.model.BatchGetItemResponse;
/**
*
* Represents the output for the
* {@link software.amazon.awssdk.services.dynamodb.DynamoDbAsyncClient#batchGetItemPaginator(software.amazon.awssdk.services.dynamodb.model.BatchGetItemRequest)}
* operation which is a paginated operation. This class is a type of {@link org.reactivestreams.Publisher} which can be
* used to provide a sequence of {@link software.amazon.awssdk.services.dynamodb.model.BatchGetItemResponse} response
* pages as per demand from the subscriber.
*
*
* When the operation is called, an instance of this class is returned. At this point, no service calls are made yet and
* so there is no guarantee that the request is valid. If there are errors in your request, you will see the failures
* only after you start streaming the data. The subscribe method should be called as a request to start streaming data.
* For more info, see {@link org.reactivestreams.Publisher#subscribe(org.reactivestreams.Subscriber)}. Each call to the
* subscribe method will result in a new {@link org.reactivestreams.Subscription} i.e., a new contract to stream data
* from the starting request.
*
*
*
* The following are few ways to use the response class:
*
* 1) Using the forEach helper method
*
*
* {@code
* software.amazon.awssdk.services.dynamodb.paginators.BatchGetItemPublisher publisher = client.batchGetItemPaginator(request);
* CompletableFuture future = publisher.forEach(res -> { // Do something with the response });
* future.get();
* }
*
*
* 2) Using a custom subscriber
*
*
* {@code
* software.amazon.awssdk.services.dynamodb.paginators.BatchGetItemPublisher publisher = client.batchGetItemPaginator(request);
* publisher.subscribe(new Subscriber() {
*
* public void onSubscribe(org.reactivestreams.Subscriber subscription) { //... };
*
*
* public void onNext(software.amazon.awssdk.services.dynamodb.model.BatchGetItemResponse response) { //... };
* });}
*
*
* As the response is a publisher, it can work well with third party reactive streams implementations like RxJava2.
*
* Note: If you prefer to have control on service calls, use the
* {@link #batchGetItem(software.amazon.awssdk.services.dynamodb.model.BatchGetItemRequest)} operation.
*
*/
@Generated("software.amazon.awssdk:codegen")
public class BatchGetItemPublisher implements SdkPublisher {
private final DynamoDbAsyncClient client;
private final BatchGetItemRequest firstRequest;
private final AsyncPageFetcher nextPageFetcher;
private boolean isLastPage;
public BatchGetItemPublisher(DynamoDbAsyncClient client, BatchGetItemRequest firstRequest) {
this(client, firstRequest, false);
}
private BatchGetItemPublisher(DynamoDbAsyncClient client, BatchGetItemRequest firstRequest, boolean isLastPage) {
this.client = client;
this.firstRequest = firstRequest;
this.isLastPage = isLastPage;
this.nextPageFetcher = new BatchGetItemResponseFetcher();
}
@Override
public void subscribe(Subscriber subscriber) {
subscriber.onSubscribe(ResponsesSubscription.builder().subscriber(subscriber).nextPageFetcher(nextPageFetcher).build());
}
/**
*
* A helper method to resume the pages in case of unexpected failures. The method takes the last successful response
* page as input and returns an instance of {@link BatchGetItemPublisher} that can be used to retrieve the
* consecutive pages that follows the input page.
*
*/
private final BatchGetItemPublisher resume(BatchGetItemResponse lastSuccessfulPage) {
if (nextPageFetcher.hasNextPage(lastSuccessfulPage)) {
return new BatchGetItemPublisher(client, firstRequest.toBuilder().requestItems(lastSuccessfulPage.unprocessedKeys())
.build());
}
return new BatchGetItemPublisher(client, firstRequest, true) {
@Override
public void subscribe(Subscriber subscriber) {
subscriber.onSubscribe(new EmptySubscription(subscriber));
}
};
}
private class BatchGetItemResponseFetcher implements AsyncPageFetcher {
@Override
public boolean hasNextPage(final BatchGetItemResponse previousPage) {
return previousPage.unprocessedKeys() != null
&& !SdkAutoConstructList.class.isInstance(previousPage.unprocessedKeys())
&& !SdkAutoConstructMap.class.isInstance(previousPage.unprocessedKeys());
}
@Override
public CompletableFuture nextPage(final BatchGetItemResponse previousPage) {
if (previousPage == null) {
return client.batchGetItem(firstRequest);
}
return client.batchGetItem(firstRequest.toBuilder().requestItems(previousPage.unprocessedKeys()).build());
}
}
}