Add support for CompletableFuture for method return types

Implements support for `CompletableFuture` on method return types by converting through RxJava `Observable`

hystrix/README.md

@@ -10,11 +10,11 @@ GitHub github = HystrixFeign.builder()
         .target(GitHub.class, "https://api.github.com");
 ```
 
-For asynchronous or reactive use, return `HystrixCommand<YourType>`.
+For asynchronous or reactive use, return `HystrixCommand<YourType>` or `CompletableFuture<YourType>`.
 
 For RxJava compatibility, use `rx.Observable<YourType>` or `rx.Single<YourType>`. Rx types are <a href="http://reactivex.io/documentation/observable.html">cold</a>, which means a http call isn't made until there's a subscriber.
 
-Methods that do *not* return [`HystrixCommand`](https://netflix.github.io/Hystrix/javadoc/com/netflix/hystrix/HystrixCommand.html), [`rx.Observable`](http://reactivex.io/RxJava/javadoc/rx/Observable.html) or [`rx.Single`] are still wrapped in a `HystrixCommand`, but `execute()` is automatically called for you.
+Methods that do *not* return [`HystrixCommand`](https://netflix.github.io/Hystrix/javadoc/com/netflix/hystrix/HystrixCommand.html), `CompletableFuture`, [`rx.Observable`](http://reactivex.io/RxJava/javadoc/rx/Observable.html) or `rx.Single` are still wrapped in a `HystrixCommand`, but `execute()` is automatically called for you.
 
 ```java
 interface YourApi {
@@ -27,6 +27,9 @@ interface YourApi {
   @RequestLine("GET /yourtype/{id}")
   Single<YourType> getYourTypeSingle(@Param("id") String id);
 
+  @RequestLine("GET /yourtype/{id}")
+  CompletableFuture<YourType> getYourTypeCompletableFuture(@Param("id") String id);
+
   @RequestLine("GET /yourtype/{id}")
   YourType getYourTypeSynchronous(@Param("id") String id);
 }
@@ -46,6 +49,9 @@ api.getYourType("a").queue();
 // for synchronous
 api.getYourType("a").execute();
 
+// or for a CompletableFuture
+api.getYourTypeCompletableFuture("a").thenApply(o -> "b");
+
 // or to apply hystrix to existing feign methods.
 api.getYourTypeSynchronous("a");
 ```

hystrix/src/main/java/feign/hystrix/HystrixDelegatingContract.java

@@ -17,6 +17,7 @@
 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 import java.util.List;
+import java.util.concurrent.CompletableFuture;
 import com.netflix.hystrix.HystrixCommand;
 import feign.Contract;
 import feign.MethodMetadata;
@@ -63,6 +64,9 @@ public List<MethodMetadata> parseAndValidatateMetadata(Class<?> targetType) {
       } else if (type instanceof ParameterizedType
           && ((ParameterizedType) type).getRawType().equals(Completable.class)) {
         metadata.returnType(void.class);
+      } else if (type instanceof ParameterizedType
+          && ((ParameterizedType) type).getRawType().equals(CompletableFuture.class)) {
+        metadata.returnType(resolveLastTypeParameter(type, CompletableFuture.class));
       }
     }
 

hystrix/src/main/java/feign/hystrix/HystrixInvocationHandler.java

@@ -22,6 +22,9 @@
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Future;
 import feign.InvocationHandlerFactory.MethodHandler;
 import feign.Target;
 import feign.Util;
@@ -130,15 +133,21 @@ protected Object getFallback() {
               } else if (isReturnsCompletable(method)) {
                 ((Completable) result).await();
                 return null;
+              } else if (isReturnsCompletableFuture(method)) {
+                return ((Future) result).get();
               } else {
                 return result;
               }
             } catch (IllegalAccessException e) {
               // shouldn't happen as method is public due to being an interface
               throw new AssertionError(e);
-            } catch (InvocationTargetException e) {
+            } catch (InvocationTargetException | ExecutionException e) {
               // Exceptions on fallback are tossed by Hystrix
               throw new AssertionError(e.getCause());
+            } catch (InterruptedException e) {
+              // Exceptions on fallback are tossed by Hystrix
+              Thread.currentThread().interrupt();
+              throw new AssertionError(e.getCause());
             }
           }
         };
@@ -155,6 +164,8 @@ protected Object getFallback() {
       return hystrixCommand.toObservable().toSingle();
     } else if (isReturnsCompletable(method)) {
       return hystrixCommand.toObservable().toCompletable();
+    } else if (isReturnsCompletableFuture(method)) {
+      return new ObservableCompletableFuture<>(hystrixCommand);
     }
     return hystrixCommand.execute();
   }
@@ -171,6 +182,10 @@ private boolean isReturnsObservable(Method method) {
     return Observable.class.isAssignableFrom(method.getReturnType());
   }
 
+  private boolean isReturnsCompletableFuture(Method method) {
+    return CompletableFuture.class.isAssignableFrom(method.getReturnType());
+  }
+
   private boolean isReturnsSingle(Method method) {
     return Single.class.isAssignableFrom(method.getReturnType());
   }

hystrix/src/main/java/feign/hystrix/ObservableCompletableFuture.java

@@ -0,0 +1,35 @@
+/**
+ * Copyright 2012-2018 The Feign Authors
+ *
+ * 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 feign.hystrix;
+
+import com.netflix.hystrix.HystrixCommand;
+import rx.Subscription;
+import java.util.concurrent.CompletableFuture;
+
+final class ObservableCompletableFuture<T> extends CompletableFuture<T> {
+
+  private final Subscription sub;
+
+  ObservableCompletableFuture(final HystrixCommand<T> command) {
+    this.sub = command.toObservable().single().subscribe(ObservableCompletableFuture.this::complete,
+        ObservableCompletableFuture.this::completeExceptionally);
+  }
+
+
+  @Override
+  public boolean cancel(final boolean b) {
+    sub.unsubscribe();
+    return super.cancel(b);
+  }
+}

hystrix/src/test/java/feign/hystrix/HystrixBuilderTest.java

@@ -26,6 +26,10 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
 import feign.FeignException;
 import feign.Headers;
 import feign.Param;
@@ -427,6 +431,66 @@ public void rxSingleListFallback() {
     assertThat(testSubscriber.getOnNextEvents().get(0)).containsExactly("fallback");
   }
 
+  @Test
+  public void completableFutureEmptyBody()
+      throws InterruptedException, ExecutionException, TimeoutException {
+    server.enqueue(new MockResponse());
+
+    TestInterface api = target();
+
+    CompletableFuture<String> completable = api.completableFuture();
+
+    assertThat(completable).isNotNull();
+
+    completable.get(5, TimeUnit.SECONDS);
+  }
+
+  @Test
+  public void completableFutureWithBody()
+      throws InterruptedException, ExecutionException, TimeoutException {
+    server.enqueue(new MockResponse().setBody("foo"));
+
+    TestInterface api = target();
+
+    CompletableFuture<String> completable = api.completableFuture();
+
+    assertThat(completable).isNotNull();
+
+    assertThat(completable.get(5, TimeUnit.SECONDS)).isEqualTo("foo");
+  }
+
+  @Test
+  public void completableFutureFailWithoutFallback() throws TimeoutException, InterruptedException {
+    server.enqueue(new MockResponse().setResponseCode(500));
+
+    TestInterface api = HystrixFeign.builder()
+        .target(TestInterface.class, "http://localhost:" + server.getPort());
+
+    CompletableFuture<String> completable = api.completableFuture();
+
+    assertThat(completable).isNotNull();
+
+    try {
+      completable.get(5, TimeUnit.SECONDS);
+    } catch (ExecutionException e) {
+      assertThat(e).hasCauseInstanceOf(HystrixRuntimeException.class);
+    }
+  }
+
+  @Test
+  public void completableFutureFallback()
+      throws InterruptedException, ExecutionException, TimeoutException {
+    server.enqueue(new MockResponse().setResponseCode(500));
+
+    TestInterface api = target();
+
+    CompletableFuture<String> completable = api.completableFuture();
+
+    assertThat(completable).isNotNull();
+
+    assertThat(completable.get(5, TimeUnit.SECONDS)).isEqualTo("fallback");
+  }
+
   @Test
   public void rxCompletableEmptyBody() {
     server.enqueue(new MockResponse());
@@ -657,6 +721,9 @@ default HystrixCommand<String> defaultMethodReturningCommand() {
 
     @RequestLine("GET /")
     Completable completable();
+
+    @RequestLine("GET /")
+    CompletableFuture<String> completableFuture();
   }
 
   class FallbackTestInterface implements TestInterface {
@@ -742,5 +809,10 @@ public List<String> getList() {
     public Completable completable() {
       return Completable.complete();
     }
+
+    @Override
+    public CompletableFuture<String> completableFuture() {
+      return CompletableFuture.completedFuture("fallback");
+    }
   }
 }