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Issue Azure#3937: Paged flux draft PR (Azure#4045)
* Initial prototype for paged flux * Update unit tests and javadocs * Remove unused imports * Updated to use paged response instead of continuation token * Update javadocs * Supplier and function * Update javadocs, add code snippets and more unit tests * Undo package-info changes * Undo package-info changes * Update javadocs * Add jsr dependency * Remove extra blank line
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core/azure-core/src/main/java/com/azure/core/http/rest/PagedFlux.java
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| // Copyright (c) Microsoft Corporation. All rights reserved. | ||
| // Licensed under the MIT License. | ||
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| package com.azure.core.http.rest; | ||
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| import java.util.Objects; | ||
| import java.util.function.Function; | ||
| import java.util.function.Supplier; | ||
| import org.reactivestreams.Publisher; | ||
| import reactor.core.CoreSubscriber; | ||
| import reactor.core.publisher.Flux; | ||
| import reactor.core.publisher.Mono; | ||
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| /** | ||
| * This class is a flux that can operate on a {@link PagedResponse} and | ||
| * also provides the ability to operate on individual items. When processing the response by page, | ||
| * each response will contain the items in the page as well as the request details like | ||
| * status code and headers. | ||
| * | ||
| * <p>To process one item at a time, simply subscribe to this flux as shown below </p> | ||
| * <p><strong>Code sample</strong></p> | ||
| * {@codesnippet com.azure.core.http.rest.pagedflux.items} | ||
| * | ||
| * <p>To process one page at a time, use {@link #byPage} method as shown below </p> | ||
| * <p><strong>Code sample</strong></p> | ||
| * {@codesnippet com.azure.core.http.rest.pagedflux.pages} | ||
| * | ||
| * <p>To process items one page at a time starting from any page associated with a continuation token, | ||
| * use {@link #byPage(String)} as shown below</p> | ||
| * <p><strong>Code sample</strong></p> | ||
| * {@codesnippet com.azure.core.http.rest.pagedflux.pagesWithContinuationToken} | ||
| * | ||
| * @param <T> The type of items in a {@link PagedResponse} | ||
| * | ||
| * @see PagedResponse | ||
| * @see Page | ||
| * @see Flux | ||
| */ | ||
| public class PagedFlux<T> extends Flux<T> { | ||
| private final Supplier<Mono<PagedResponse<T>>> firstPageRetriever; | ||
| private final Function<String, Mono<PagedResponse<T>>> nextPageRetriever; | ||
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| /** | ||
| * Creates an instance of {@link PagedFlux}. The constructor takes in two arguments. The first | ||
| * argument is a supplier that fetches the first page of {@code T}. The second argument is a | ||
| * function that fetches subsequent pages of {@code T} | ||
| * <p><strong>Code sample</strong></p> | ||
| * {@codesnippet com.azure.core.http.rest.pagedflux.instantiation} | ||
| * | ||
| * @param firstPageRetriever Supplier that retrieves the first page | ||
| * @param nextPageRetriever Function that retrieves the next page given a continuation token | ||
| */ | ||
| public PagedFlux(Supplier<Mono<PagedResponse<T>>> firstPageRetriever, | ||
| Function<String, Mono<PagedResponse<T>>> nextPageRetriever) { | ||
| Objects.requireNonNull(firstPageRetriever, "First page supplier cannot be null"); | ||
| Objects.requireNonNull(nextPageRetriever, "Next page retriever function cannot be null"); | ||
| this.firstPageRetriever = firstPageRetriever; | ||
| this.nextPageRetriever = nextPageRetriever; | ||
| } | ||
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| /** | ||
| * Creates a flux of {@link PagedResponse} starting from the first page. | ||
| * | ||
| * <p><strong>Code sample</strong></p> | ||
| * {@codesnippet com.azure.core.http.rest.pagedflux.bypage} | ||
| * | ||
| * @return A {@link PagedFlux} starting from the first page | ||
| */ | ||
| public Flux<PagedResponse<T>> byPage() { | ||
| return firstPageRetriever.get().flatMapMany(this::extractAndFetchPage); | ||
| } | ||
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| /** | ||
| * Creates a flux of {@link PagedResponse} starting from the next page associated with the given | ||
| * continuation token. To start from first page, use {@link #byPage()} instead. | ||
| * | ||
| * <p><strong>Code sample</strong></p> | ||
| * {@codesnippet com.azure.core.http.rest.pagedflux.bypage#String} | ||
| * | ||
| * @param continuationToken The continuation token used to fetch the next page | ||
| * @return A {@link PagedFlux} starting from the page associated with the continuation token | ||
| */ | ||
| public Flux<PagedResponse<T>> byPage(String continuationToken) { | ||
| return nextPageRetriever.apply(continuationToken).flatMapMany(this::extractAndFetchPage); | ||
| } | ||
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| /** | ||
| * Subscribe to consume all items of type {@code T} in the sequence respectively. | ||
| * This is recommended for most common scenarios. This will seamlessly fetch next | ||
| * page when required and provide with a {@link Flux} of items. | ||
| * | ||
| * <p><strong>Code sample</strong></p> | ||
| * {@codesnippet com.azure.core.http.rest.pagedflux.subscribe} | ||
| * | ||
| * @param coreSubscriber The subscriber for this {@link PagedFlux} | ||
| */ | ||
| @Override | ||
| public void subscribe(CoreSubscriber<? super T> coreSubscriber) { | ||
| byT(null).subscribe(coreSubscriber); | ||
| } | ||
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| /** | ||
| * Helper method to return the flux of items starting from the page associated with the {@code continuationToken} | ||
| * | ||
| * @param continuationToken The continuation token that is used to fetch the next page | ||
| * @return A {@link Flux} of items in this page | ||
| */ | ||
| private Flux<T> byT(String continuationToken) { | ||
| if (continuationToken == null) { | ||
| return firstPageRetriever.get().flatMapMany(this::extractAndFetchT); | ||
| } | ||
| return nextPageRetriever.apply(continuationToken).flatMapMany(this::extractAndFetchT); | ||
| } | ||
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| /** | ||
| * Helper method to string together a flux of items transparently extracting items from | ||
| * next pages, if available. | ||
| * @param page Starting page | ||
| * @return A {@link Flux} of items | ||
| */ | ||
| private Publisher<T> extractAndFetchT(PagedResponse<T> page) { | ||
| String nextPageLink = page.nextLink(); | ||
| if (nextPageLink == null) { | ||
| return Flux.fromIterable(page.items()); | ||
| } | ||
| return Flux.fromIterable(page.items()).concatWith(byT(nextPageLink)); | ||
| } | ||
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| /** | ||
| * Helper method to string together a flux of {@link PagedResponse} transparently | ||
| * fetching next pages, if available | ||
| * @param page Starting page | ||
| * @return A {@link Flux} of {@link PagedResponse} | ||
| */ | ||
| private Publisher<? extends PagedResponse<T>> extractAndFetchPage(PagedResponse<T> page) { | ||
| return Flux.just(page).concatWith(byPage(page.nextLink())); | ||
| } | ||
| } |
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