Add support of CompletionStage

Author: Sebastien GREGOIRE

modules/swagger-jaxrs2/src/main/java/io/swagger/v3/jaxrs2/Reader.java

@@ -69,6 +69,7 @@
 import java.util.Optional;
 import java.util.Set;
 import java.util.TreeSet;
+import java.util.concurrent.CompletionStage;
 import java.util.stream.Collectors;
 
 public class Reader implements OpenApiReader {
@@ -1071,7 +1072,7 @@ protected Operation parseMethod(
         Type returnType = method.getGenericReturnType();
 
         if (annotatedMethod != null && annotatedMethod.getType() != null) {
-            returnType = annotatedMethod.getType();
+            returnType = extractTypeFromMethod(annotatedMethod);
         }
 
         final Class<?> subResource = getSubResourceWithJaxRsSubresourceLocatorSpecs(method);
@@ -1133,6 +1134,14 @@ protected Operation parseMethod(
         return operation;
     }
 
+    private Type extractTypeFromMethod(AnnotatedMethod annotatedMethod) {
+        if(CompletionStage.class.isAssignableFrom(annotatedMethod.getType().getRawClass())) {
+            // CompletionStage's 1st generic type is the real return type.
+            return annotatedMethod.getType().getBindings().getBoundType(0);
+        }
+        return annotatedMethod.getType();
+    }
+
     protected Content resolveEmptyContent(Produces classProduces, Produces methodProduces) {
         Content content = new Content();
         MediaType mediaType = new MediaType();

modules/swagger-jaxrs2/src/test/java/io/swagger/v3/jaxrs2/ReaderTest.java

@@ -125,7 +125,10 @@
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionStage;
 import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.stream.Collectors;
 
 import static org.testng.Assert.assertEquals;
 import static org.testng.Assert.assertFalse;
@@ -717,6 +720,36 @@ public void test1(A a) {
         }
     }
 
+    @Test
+    public void testClassWithCompletableFuture() {
+        Reader reader = new Reader(new OpenAPI());
+        OpenAPI openAPI = reader.read(ClassWithCompletableFuture.class);
+        assertNotNull(openAPI);
+
+        assertEquals(
+            openAPI.getPaths()
+                    .get("/myApi")
+                    .getGet()
+                    .getResponses()
+                    .get("default")
+                    .getContent()
+                    .get("application/json")
+                    .getSchema()
+                    .get$ref(),
+                "#/components/schemas/Ret"
+        );
+    }
+
+    static class ClassWithCompletableFuture {
+        @Path("/myApi")
+        @Produces("application/json")
+        @Consumes("application/json")
+        @GET
+        public CompletableFuture<Ret> myApi(A a) {
+            return CompletableFuture.completedFuture(new Ret());
+        }
+    }
+
     @Test(description = "test resource with array in response content")
     public void test2497() {
         Reader reader = new Reader(new OpenAPI());