Add AsyncPage implementation and docs. Add related tests

gcloud-java-core/src/main/java/com/google/cloud/AsyncPage.java

@@ -18,6 +18,34 @@
 
 import java.util.concurrent.Future;
 
+/**
+ * Interface for asynchronously consuming Google Cloud paginated results.
+ *
+ * <p>Use {@code AsyncPage} to iterate through all values (also in next pages):
+ * <pre> {@code
+ * AsyncPage<T> page = ...; // get an AsyncPage<T> instance
+ * Iterator<T> iterator = page.iterateAll();
+ * while (iterator.hasNext()) {
+ *   T value = iterator.next();
+ *   // do something with value
+ * }}</pre>
+ *
+ * <p>Or handle pagination explicitly:
+ * <pre> {@code
+ * AsyncPage<T> page = ...; // get a AsyncPage<T> instance
+ * while (page != null) {
+ *   for (T value : page.values()) {
+ *     // do something with value
+ *   }
+ *   page = page.nextPage().get();
+ * }}</pre>
+ *
+ * @param <T> the value type that the page holds
+ */
 public interface AsyncPage<T> extends Page<T> {
+
+  /**
+   * Returns a {@link Future} object for the next page.
+   */
   Future<AsyncPage<T>> nextPageAsync();
 }

gcloud-java-core/src/main/java/com/google/cloud/AsyncPageImpl.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2016 Google Inc. 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.
+ * You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License 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 com.google.cloud;
+
+import com.google.common.base.Throwables;
+import com.google.common.util.concurrent.Uninterruptibles;
+
+import java.io.Serializable;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Future;
+
+/**
+ * Base implementation for asynchronously consuming Google Cloud paginated results.
+ *
+ * @param <T> the value type that the page holds
+ */
+public class AsyncPageImpl<T> extends PageImpl<T> implements AsyncPage<T> {
+
+  private static final long serialVersionUID = -6009473188630364906L;
+
+  private final NextPageFetcher<T> asyncPageFetcher;
+
+  /**
+   * Interface for asynchronously fetching the next page of results from the service.
+   *
+   * @param <T> the value type that the page holds
+   */
+  public interface NextPageFetcher<T> extends Serializable {
+    Future<AsyncPage<T>> nextPage();
+  }
+
+  private static class SyncNextPageFetcher<T> implements PageImpl.NextPageFetcher<T> {
+
+    private static final long serialVersionUID = -4124568632363525351L;
+
+    private NextPageFetcher<T> asyncPageFetcher;
+
+    private SyncNextPageFetcher(NextPageFetcher<T> asyncPageFetcher) {
+      this.asyncPageFetcher = asyncPageFetcher;
+    }
+
+    @Override
+    public Page<T> nextPage() {
+      try {
+        return asyncPageFetcher != null
+            ? Uninterruptibles.getUninterruptibly(asyncPageFetcher.nextPage()) : null;
+      } catch (ExecutionException ex) {
+        throw Throwables.propagate(ex.getCause());
+      }
+    }
+  }
+
+  /**
+   * Creates an {@code AsyncPageImpl} object.
+   */
+  public AsyncPageImpl(NextPageFetcher<T> asyncPageFetcher, String cursor, Iterable<T> results) {
+    super(new SyncNextPageFetcher<T>(asyncPageFetcher), cursor, results);
+    this.asyncPageFetcher = asyncPageFetcher;
+  }
+
+  @Override
+  public Future<AsyncPage<T>> nextPageAsync() {
+    if (nextPageCursor() == null || asyncPageFetcher == null) {
+      return null;
+    }
+    return asyncPageFetcher.nextPage();
+  }
+}

gcloud-java-core/src/test/java/com/google/cloud/AsyncPageImplTest.java

@@ -0,0 +1,128 @@
+/*
+ * Copyright 2016 Google Inc. 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.
+ * You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License 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 com.google.cloud;
+
+import static org.junit.Assert.assertEquals;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.util.concurrent.Futures;
+
+import org.junit.Test;
+
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Future;
+
+public class AsyncPageImplTest {
+
+  private static final ImmutableList<String> VALUES1 = ImmutableList.of("1", "2");
+  private static final ImmutableList<String> VALUES2 = ImmutableList.of("3", "4");
+  private static final ImmutableList<String> VALUES3 = ImmutableList.of("5", "6");
+  private static final ImmutableList<String> ALL_VALUES = ImmutableList.<String>builder()
+      .addAll(VALUES1)
+      .addAll(VALUES2)
+      .addAll(VALUES3)
+      .build();
+  private static final ImmutableList<String> SOME_VALUES = ImmutableList.<String>builder()
+      .addAll(VALUES2)
+      .addAll(VALUES3)
+      .build();
+
+  @Test
+  public void testPage() {
+    final AsyncPageImpl<String> nextResult = new AsyncPageImpl<>(null, "c", VALUES2);
+    AsyncPageImpl.NextPageFetcher<String> fetcher = new AsyncPageImpl.NextPageFetcher<String>() {
+      private static final long serialVersionUID = 4703765400378593176L;
+
+      @Override
+      public Future<AsyncPage<String>> nextPage() {
+        return Futures.<AsyncPage<String>>immediateFuture(nextResult);
+      }
+    };
+    AsyncPageImpl<String> result = new AsyncPageImpl<>(fetcher, "c", VALUES1);
+    assertEquals(nextResult, result.nextPage());
+    assertEquals("c", result.nextPageCursor());
+    assertEquals(VALUES1, result.values());
+  }
+
+  @Test
+  public void testPageAsync() throws ExecutionException, InterruptedException {
+    final AsyncPageImpl<String> nextResult = new AsyncPageImpl<>(null, "c", VALUES2);
+    AsyncPageImpl.NextPageFetcher<String> fetcher = new AsyncPageImpl.NextPageFetcher<String>() {
+      private static final long serialVersionUID = 4703765400378593176L;
+
+      @Override
+      public Future<AsyncPage<String>> nextPage() {
+        return Futures.<AsyncPage<String>>immediateFuture(nextResult);
+      }
+    };
+    AsyncPageImpl<String> result = new AsyncPageImpl<>(fetcher, "c", VALUES1);
+    assertEquals(nextResult, result.nextPageAsync().get());
+    assertEquals("c", result.nextPageCursor());
+    assertEquals(VALUES1, result.values());
+  }
+
+  @Test
+  public void testIterateAll() {
+    final AsyncPageImpl<String> nextResult2 = new AsyncPageImpl<>(null, "c3", VALUES3);
+    AsyncPageImpl.NextPageFetcher<String> fetcher2 = new AsyncPageImpl.NextPageFetcher<String>() {
+      private static final long serialVersionUID = -9203621430631884026L;
+
+      @Override
+      public Future<AsyncPage<String>> nextPage() {
+        return Futures.<AsyncPage<String>>immediateFuture(nextResult2);
+      }
+    };
+    final AsyncPageImpl<String> nextResult1 = new AsyncPageImpl<>(fetcher2, "c2", VALUES2);
+    AsyncPageImpl.NextPageFetcher<String> fetcher1 = new AsyncPageImpl.NextPageFetcher<String>() {
+      private static final long serialVersionUID = -9203621430631884026L;
+
+      @Override
+      public Future<AsyncPage<String>> nextPage() {
+        return Futures.<AsyncPage<String>>immediateFuture(nextResult1);
+      }
+    };
+    AsyncPageImpl<String> result = new AsyncPageImpl<>(fetcher1, "c1", VALUES1);
+    assertEquals(ALL_VALUES, ImmutableList.copyOf(result.iterateAll()));
+  }
+
+  @Test
+  public void testAsyncPageAndIterateAll() throws ExecutionException, InterruptedException {
+    final AsyncPageImpl<String> nextResult2 = new AsyncPageImpl<>(null, "c3", VALUES3);
+    AsyncPageImpl.NextPageFetcher<String> fetcher2 = new AsyncPageImpl.NextPageFetcher<String>() {
+      private static final long serialVersionUID = -9203621430631884026L;
+
+      @Override
+      public Future<AsyncPage<String>> nextPage() {
+        return Futures.<AsyncPage<String>>immediateFuture(nextResult2);
+      }
+    };
+    final AsyncPageImpl<String> nextResult1 = new AsyncPageImpl<>(fetcher2, "c2", VALUES2);
+    AsyncPageImpl.NextPageFetcher<String> fetcher1 = new AsyncPageImpl.NextPageFetcher<String>() {
+      private static final long serialVersionUID = -9203621430631884026L;
+
+      @Override
+      public Future<AsyncPage<String>> nextPage() {
+        return Futures.<AsyncPage<String>>immediateFuture(nextResult1);
+      }
+    };
+    AsyncPageImpl<String> result = new AsyncPageImpl<>(fetcher1, "c1", VALUES1);
+    assertEquals(nextResult1, result.nextPageAsync().get());
+    assertEquals("c1", result.nextPageCursor());
+    assertEquals(VALUES1, result.values());
+    assertEquals(SOME_VALUES, ImmutableList.copyOf(result.nextPageAsync().get().iterateAll()));
+  }
+}

gcloud-java-core/src/test/java/com/google/cloud/PageImplTest.java

@@ -35,6 +35,8 @@ public class PageImplTest {
   public void testPage() {
     final PageImpl<String> nextResult = new PageImpl<>(null, "c", NEXT_VALUES);
     PageImpl.NextPageFetcher<String> fetcher = new PageImpl.NextPageFetcher<String>() {
+      private static final long serialVersionUID = -1714571149183431798L;
+
       @Override
       public PageImpl<String> nextPage() {
         return nextResult;