Fix Paging Samples That Produce NullPointerExceptions (#15997)

* Fix paging samples that produce NullPointerExceptions

* Fix linting issue

sdk/core/azure-core/src/samples/java/com/azure/core/http/rest/PagedFluxBaseJavaDocCodeSnippets.java

@@ -62,6 +62,7 @@ public void classDocSnippet() {
 
     /**
      * Code snippets for creating an instance of {@link PagedFluxBase}
+     *
      * @return An instance of {@link PagedFluxBase}
      */
     private PagedFluxBase<Integer, PagedResponse<Integer>> createAnInstance() {
@@ -82,8 +83,9 @@ private PagedFluxBase<Integer, PagedResponse<Integer>> createAnInstance() {
         // A supplier that fetches the first page of data from source/service
         Supplier<Mono<PagedResponse<Integer>>> firstPageRetrieverFunction = () -> getFirstPage();
 
-        PagedFluxBase<Integer, PagedResponse<Integer>> pagedFluxBaseInstance = new PagedFluxBase<>(firstPageRetrieverFunction,
-            nextPageRetriever);
+        PagedFluxBase<Integer, PagedResponse<Integer>> pagedFluxBaseInstance =
+            new PagedFluxBase<>(firstPageRetrieverFunction,
+                nextPageRetriever);
         // END: com.azure.core.http.rest.pagedfluxbase.singlepage.instantiation
         return pagedFluxBase;
     }
@@ -128,22 +130,22 @@ public void byTSnippet() {
 
         // BEGIN: com.azure.core.http.rest.pagedfluxbase.subscribe
         pagedFluxBase.subscribe(new BaseSubscriber<Integer>() {
-                @Override
-                protected void hookOnSubscribe(Subscription subscription) {
-                    System.out.println("Subscribed to paged flux processing items");
-                    super.hookOnSubscribe(subscription);
-                }
-
-                @Override
-                protected void hookOnNext(Integer value) {
-                    System.out.println("Processing item with value: " + value);
-                }
-
-                @Override
-                protected void hookOnComplete() {
-                    System.out.println("Processing complete.");
-                }
-            });
+            @Override
+            protected void hookOnSubscribe(Subscription subscription) {
+                System.out.println("Subscribed to paged flux processing items");
+                super.hookOnSubscribe(subscription);
+            }
+
+            @Override
+            protected void hookOnNext(Integer value) {
+                System.out.println("Processing item with value: " + value);
+            }
+
+            @Override
+            protected void hookOnComplete() {
+                System.out.println("Processing complete.");
+            }
+        });
         // END: com.azure.core.http.rest.pagedfluxbase.subscribe
     }
 

sdk/core/azure-core/src/samples/java/com/azure/core/http/rest/PagedIterableBaseJavaDocCodeSnippets.java

@@ -3,10 +3,11 @@
 
 package com.azure.core.http.rest;
 
+import reactor.core.publisher.Mono;
+
 import java.util.Iterator;
 import java.util.function.Function;
 import java.util.function.Supplier;
-import reactor.core.publisher.Mono;
 
 /**
  * Code snippets for {@link PagedIterableBase}
@@ -94,7 +95,7 @@ public void iterableByPageWhileSnippet() {
      *
      * @return An instance of {@link PagedFlux}
      */
-    public CustomPagedFlux<String> createCustomInstance() {
+    CustomPagedFlux<String> createCustomInstance() {
 
         // A supplier that fetches the first page of data from source/service
         Supplier<Mono<PagedResponse<String>>> firstPageRetriever = () -> null;

sdk/core/azure-core/src/samples/java/com/azure/core/http/rest/PagedIterableJavaDocCodeSnippets.java

@@ -3,11 +3,18 @@
 
 package com.azure.core.http.rest;
 
+import com.azure.core.http.HttpHeaders;
+import com.azure.core.http.HttpMethod;
+import com.azure.core.http.HttpRequest;
 import reactor.core.publisher.Mono;
 
 import java.util.Iterator;
+import java.util.List;
+import java.util.UUID;
 import java.util.function.Function;
 import java.util.function.Supplier;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
 
 /**
  * Code snippets for {@link PagedIterable}
@@ -91,28 +98,51 @@ public PagedFlux<Integer> createAnInstance() {
         Function<String, Mono<PagedResponse<Integer>>> nextPageRetriever =
             continuationToken -> getNextPage(continuationToken);
 
-        PagedFlux<Integer> pagedFlux = new PagedFlux<>(firstPageRetriever,
-            nextPageRetriever);
-        return pagedFlux;
+        return new PagedFlux<>(firstPageRetriever, nextPageRetriever);
     }
 
 
     /**
-     * Implementation not provided
+     * Retrieves the next page from a paged API.
      *
      * @param continuationToken Token to fetch the next page
      * @return A {@link Mono} of {@link PagedResponse} containing items of type {@code Integer}
      */
     private Mono<PagedResponse<Integer>> getNextPage(String continuationToken) {
-        return null;
+        return getPage(continuationToken);
     }
 
     /**
-     * Implementation not provided
+     * Retrieves the initial page from a paged API.
      *
      * @return A {@link Mono} of {@link PagedResponse} containing items of type {@code Integer}
      */
     private Mono<PagedResponse<Integer>> getFirstPage() {
-        return null;
+        return getPage(null);
+    }
+
+    /**
+     * Retrieves a page from a paged API.
+     *
+     * @param continuationToken Token to fetch the next page, if {@code null} the first page is retrieved.
+     * @return A {@link Mono} of {@link PagedResponse} containing items of type {@code Integer}
+     */
+    private Mono<PagedResponse<Integer>> getPage(String continuationToken) {
+        // Given this isn't calling an actual API we will arbitrarily generate a continuation token or end paging.
+        boolean lastPage = Math.random() > 0.5;
+
+        // If it is the last page there should be no additional continuation tokens returned.
+        String nextContinuationToken = lastPage ? null : UUID.randomUUID().toString();
+
+        // Arbitrarily begin the next page of integers.
+        int elementCount = (int) Math.ceil(Math.random() * 15);
+        List<Integer> elements = IntStream.range(elementCount, elementCount + elementCount)
+            .map(val -> (int) (Math.random() * val))
+            .boxed()
+            .collect(Collectors.toList());
+
+        // This is a rough approximation of a service response.
+        return Mono.just(new PagedResponseBase<Void, Integer>(new HttpRequest(HttpMethod.GET, "https://requestUrl.com"),
+            200, new HttpHeaders(), elements, nextContinuationToken, null));
     }
 }

sdk/core/azure-core/src/samples/java/com/azure/core/util/paging/PagedFluxCoreJavaDocCodeSnippets.java

@@ -6,6 +6,9 @@
 import com.azure.core.util.IterableStream;
 import reactor.core.publisher.Flux;
 
+import java.util.Collections;
+import java.util.List;
+import java.util.UUID;
 import java.util.function.Supplier;
 
 /**
@@ -40,44 +43,69 @@ boolean isDone() {
         }
 
         class FileContinuationToken {
+            private final int nextLinkId;
+
+            FileContinuationToken(int nextLinkId) {
+                this.nextLinkId = nextLinkId;
+            }
+
             public int getNextLinkId() {
-                return 0;
+                return nextLinkId;
             }
         }
 
         class File {
+            private final String guid;
+
+            File(String guid) {
+                this.guid = guid;
+            }
+
+            public String getGuid() {
+                return guid;
+            }
         }
 
         class FilePage implements ContinuablePage<FileContinuationToken, File> {
+            private final IterableStream<File> elements;
+            private final FileContinuationToken fileContinuationToken;
+
+            FilePage(List<File> elements, FileContinuationToken fileContinuationToken) {
+                this.elements = IterableStream.of(elements);
+                this.fileContinuationToken = fileContinuationToken;
+            }
+
             @Override
             public IterableStream<File> getElements() {
-                return null;
+                return elements;
             }
 
             @Override
             public FileContinuationToken getContinuationToken() {
-                return null;
+                return fileContinuationToken;
             }
         }
 
         class FileShareServiceClient {
             Flux<FilePage> getFilePages(FileContinuationToken token) {
-                return null;
+                List<File> files = Collections.singletonList(new File(UUID.randomUUID().toString()));
+                if (token.getNextLinkId() < 10) {
+                    return Flux.just(new FilePage(files, null));
+                } else {
+                    return Flux.just(new FilePage(files,
+                        new FileContinuationToken((int) Math.floor(Math.random() * 20))));
+                }
             }
         }
-        FileShareServiceClient client = null; // Initialize client
 
-        Supplier<PageRetriever<FileContinuationToken, FilePage>> pageRetrieverProvider
-            = new Supplier<PageRetriever<FileContinuationToken, FilePage>>() {
-                @Override
-                public PageRetriever<FileContinuationToken, FilePage> get() {
-                    return (continuationToken, pageSize) -> client.getFilePages(continuationToken);
-                }
-            };
+        FileShareServiceClient client = new FileShareServiceClient();
+
+        Supplier<PageRetriever<FileContinuationToken, FilePage>> pageRetrieverProvider = () ->
+            (continuationToken, pageSize) -> client.getFilePages(continuationToken);
 
         class FilePagedFlux extends ContinuablePagedFluxCore<FileContinuationToken, File, FilePage> {
             FilePagedFlux(Supplier<PageRetriever<FileContinuationToken, FilePage>>
-                                     pageRetrieverProvider) {
+                pageRetrieverProvider) {
                 super(pageRetrieverProvider);
             }
         }