Double check that a Function can return a Mono

spring-cloud-function-web/src/main/java/org/springframework/cloud/function/web/flux/FunctionController.java

@@ -16,6 +16,7 @@
 
 package org.springframework.cloud.function.web.flux;
 
+import java.util.Collection;
 import java.util.Optional;
 import java.util.function.Consumer;
 import java.util.function.Function;
@@ -124,12 +125,24 @@ public class FunctionController {
 			return Mono.from(result);
 		}
 
+		if (isInputMultiple(handler) && isOutputSingle(handler)) {
+			request.setAttribute(WebRequestConstants.OUTPUT_SINGLE, true,
+					WebRequest.SCOPE_REQUEST);
+			return Mono.from(result);
+		}
+
 		request.setAttribute(WebRequestConstants.OUTPUT_SINGLE, false,
 				WebRequest.SCOPE_REQUEST);
 
 		return result;
 	}
 
+	private boolean isInputMultiple(Object handler) {
+		Class<?> type = inspector.getInputType(handler);
+		Class<?> wrapper = inspector.getInputWrapper(handler);
+		return Collection.class.isAssignableFrom(type) || Flux.class.equals(wrapper);
+	}
+
 	private boolean isOutputSingle(Object handler) {
 		Class<?> type = inspector.getOutputType(handler);
 		Class<?> wrapper = inspector.getOutputWrapper(handler);

spring-cloud-function-web/src/test/java/org/springframework/cloud/function/web/RestApplicationTests.java

@@ -15,10 +15,24 @@
  */
 package org.springframework.cloud.function.web;
 
+import java.net.URI;
+import java.time.Duration;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Consumer;
+import java.util.function.Function;
+import java.util.function.Supplier;
+import java.util.stream.Collectors;
+
 import org.junit.Before;
 import org.junit.Ignore;
 import org.junit.Test;
 import org.junit.runner.RunWith;
+
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.annotation.Qualifier;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
@@ -38,18 +52,12 @@ import org.springframework.test.context.junit4.SpringRunner;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 import org.springframework.util.StringUtils;
-import reactor.core.publisher.Flux;
-
-import java.net.URI;
-import java.time.Duration;
-import java.util.*;
-import java.util.function.Consumer;
-import java.util.function.Function;
-import java.util.function.Supplier;
-import java.util.stream.Collectors;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
 /**
  * @author Dave Syer
  */
@@ -219,7 +227,7 @@ public class RestApplicationTests {
 		assertThat(rest.exchange(
 				RequestEntity.get(new URI("/sentences")).accept(MediaType.ALL).build(),
 				String.class).getBody())
-				.isEqualTo("[[\"go\",\"home\"],[\"come\",\"back\"]]");
+						.isEqualTo("[[\"go\",\"home\"],[\"come\",\"back\"]]");
 	}
 
 	@Test
@@ -418,7 +426,7 @@ public class RestApplicationTests {
 						// The new line in the middle is optional
 						.body("[{\"value\":\"foo\"},\n{\"value\":\"bar\"}]"),
 				String.class).getBody())
-				.isEqualTo("[{\"value\":\"FOO\"},{\"value\":\"BAR\"}]");
+						.isEqualTo("[{\"value\":\"FOO\"},{\"value\":\"BAR\"}]");
 	}
 
 	@Test
@@ -426,7 +434,7 @@ public class RestApplicationTests {
 		assertThat(rest.exchange(RequestEntity.post(new URI("/uppercase"))
 				.accept(EVENT_STREAM).contentType(MediaType.APPLICATION_JSON)
 				.body("[\"foo\",\"bar\"]"), String.class).getBody())
-				.isEqualTo(sse("(FOO)", "(BAR)"));
+						.isEqualTo(sse("(FOO)", "(BAR)"));
 	}
 
 	@Test
@@ -437,10 +445,19 @@ public class RestApplicationTests {
 		map.put("A", Arrays.asList("1", "2", "3"));
 		map.put("B", Arrays.asList("5", "6"));
 
-		assertThat(rest.exchange(RequestEntity.post(new URI("/sum"))
-				.accept(MediaType.APPLICATION_JSON).contentType(MediaType.MULTIPART_FORM_DATA)
-				.body(map), String.class).getBody())
-				.isEqualTo("[{\"A\":6,\"B\":11}]");
+		assertThat(rest.exchange(
+				RequestEntity.post(new URI("/sum")).accept(MediaType.APPLICATION_JSON)
+						.contentType(MediaType.MULTIPART_FORM_DATA).body(map),
+				String.class).getBody()).isEqualTo("[{\"A\":6,\"B\":11}]");
+	}
+
+	@Test
+	public void count() throws Exception {
+		List<String> list = Arrays.asList("A", "B", "A");
+		assertThat(rest.exchange(
+				RequestEntity.post(new URI("/count")).accept(MediaType.APPLICATION_JSON)
+						.contentType(MediaType.APPLICATION_JSON).body(list),
+				String.class).getBody()).isEqualTo("{\"A\":2,\"B\":1}");
 	}
 
 	private String sse(String... values) {
@@ -594,18 +611,16 @@ public class RestApplicationTests {
 
 		@Bean
 		public Function<MultiValueMap<String, String>, Map<String, Integer>> sum() {
-			return valueMap -> valueMap
-					.entrySet()
-					.stream()
-					.collect(
-							Collectors
-									.toMap(
-											Map.Entry::getKey,
-											values -> values.getValue().stream().mapToInt(Integer::parseInt).sum()
-									)
-					);
+			return valueMap -> valueMap.entrySet().stream()
+					.collect(Collectors.toMap(Map.Entry::getKey, values -> values
+							.getValue().stream().mapToInt(Integer::parseInt).sum()));
 		}
 
+		@Bean
+		public Function<Flux<String>, Mono<Map<String, Integer>>> count() {
+			return flux -> flux.collect(HashMap::new,
+					(map, word) -> map.merge(word, 1, Integer::sum));
+		}
 	}
 
 	public static class Foo {