Merge pull request #2962 from square/jakew/completable-future-android/2018-11-16

Enable built-in CompletableFuture adapter on Android API 24+

Author: swankjesse

retrofit/src/main/java/retrofit2/CompletableFutureCallAdapterFactory.java

@@ -15,36 +15,14 @@
  */
 package retrofit2;
 
-import java.io.IOException;
 import java.lang.annotation.Annotation;
 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 import java.util.concurrent.CompletableFuture;
 import javax.annotation.Nullable;
 import org.codehaus.mojo.animal_sniffer.IgnoreJRERequirement;
 
-/**
- * A {@linkplain CallAdapter.Factory call adapter} which creates Java 8 futures.
- * <p>
- * Adding this class to {@link Retrofit} allows you to return {@link CompletableFuture} from
- * service methods.
- * <pre><code>
- * interface MyService {
- *   &#64;GET("user/me")
- *   CompletableFuture&lt;User&gt; getUser()
- * }
- * </code></pre>
- * There are two configurations supported for the {@code CompletableFuture} type parameter:
- * <ul>
- * <li>Direct body (e.g., {@code CompletableFuture<User>}) returns the deserialized body for 2XX
- * responses, sets {@link retrofit2.HttpException HttpException} errors for non-2XX responses, and
- * sets {@link IOException} for network errors.</li>
- * <li>Response wrapped body (e.g., {@code CompletableFuture<Response<User>>}) returns a
- * {@link Response} object for all HTTP responses and sets {@link IOException} for network
- * errors</li>
- * </ul>
- */
-@IgnoreJRERequirement
+@IgnoreJRERequirement // Only added when CompletableFuture is available (Java 8+ / Android API 24+).
 final class CompletableFutureCallAdapterFactory extends CallAdapter.Factory {
   static final CallAdapter.Factory INSTANCE = new CompletableFutureCallAdapterFactory();
 

retrofit/src/main/java/retrofit2/Platform.java

@@ -28,6 +28,7 @@
 import javax.annotation.Nullable;
 import org.codehaus.mojo.animal_sniffer.IgnoreJRERequirement;
 
+import static java.util.Arrays.asList;
 import static java.util.Collections.emptyList;
 import static java.util.Collections.singletonList;
 import static java.util.Collections.unmodifiableList;
@@ -147,7 +148,14 @@ static class Android extends Platform {
     @Override List<? extends CallAdapter.Factory> defaultCallAdapterFactories(
         @Nullable Executor callbackExecutor) {
       if (callbackExecutor == null) throw new AssertionError();
-      return singletonList(new ExecutorCallAdapterFactory(callbackExecutor));
+      ExecutorCallAdapterFactory executorFactory = new ExecutorCallAdapterFactory(callbackExecutor);
+      return Build.VERSION.SDK_INT >= 24
+        ? asList(CompletableFutureCallAdapterFactory.INSTANCE, executorFactory)
+        : singletonList(executorFactory);
+    }
+
+    @Override int defaultCallAdapterFactoriesSize() {
+      return Build.VERSION.SDK_INT >= 24 ? 2 : 1;
     }
 
     @Override List<? extends Converter.Factory> defaultConverterFactories() {

retrofit/src/test/java/retrofit2/CompletableFutureAndroidTest.java

@@ -0,0 +1,72 @@
+/*
+ * Copyright (C) 2016 Square, Inc.
+ *
+ * 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 retrofit2;
+
+import java.util.concurrent.CompletableFuture;
+import okhttp3.mockwebserver.MockResponse;
+import okhttp3.mockwebserver.MockWebServer;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.annotation.Config;
+import retrofit2.helpers.ToStringConverterFactory;
+import retrofit2.http.GET;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.Assert.fail;
+import static org.robolectric.annotation.Config.NEWEST_SDK;
+
+@RunWith(RobolectricTestRunner.class)
+@Config(sdk = NEWEST_SDK)
+public final class CompletableFutureAndroidTest {
+  @Rule public final MockWebServer server = new MockWebServer();
+
+  interface Service {
+    @GET("/") CompletableFuture<String> endpoint();
+  }
+
+  private Service service;
+
+  @Before public void setUp() {
+    Retrofit retrofit = new Retrofit.Builder()
+        .baseUrl(server.url("/"))
+        .addConverterFactory(new ToStringConverterFactory())
+        .build();
+    service = retrofit.create(Service.class);
+  }
+
+  @Config(sdk = 24)
+  @Test public void completableFutureApi24() throws Exception {
+    server.enqueue(new MockResponse().setBody("Hi"));
+
+    CompletableFuture<String> future = service.endpoint();
+    assertThat(future.get()).isEqualTo("Hi");
+  }
+
+  @Config(sdk = 21)
+  @Test public void completableFuturePreApi24() {
+    try {
+      service.endpoint();
+      fail();
+    } catch (IllegalArgumentException e) {
+      assertThat(e).hasMessage(
+          "Unable to create call adapter for java.util.concurrent.CompletableFuture<java.lang.String>\n"
+              + "    for method Service.endpoint");
+    }
+  }
+}