[Java] [Spring] Fix reactive return type for list (#16884)

* Improve Add Async - Spring Cloud test

By testing the generated code.
This will be used to detect regressions.

* Spring: Fix reactive return type for list

Fix for #16883.

When *reactive* is enabled and response entities is *disabled*,
use `Flux<Item>` to stream the output instead of `Mono<Flux<Item>>`
With Spring Reactive, the expected return type for an array of item is
`Flux<Item>`.
Without this patch, the generated code is `Mono<Flux<Item>>`.

This is fixed by introducing specific handling for return types when
reactive is enabled.
In particular, "responseWrapper" is not used anymore in such situations.

* Fix methodBody

* Fix invalid test

* Fix SSE

* Fix methodBody when isArray and useResponseEntity

* methodBody: Flux.empty() instead of s -> {}

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/SpringCodegen.java

@@ -669,7 +669,12 @@ public class SpringCodegen extends AbstractJavaCodegen
             additionalProperties.put(RESPONSE_WRAPPER, "CompletableFuture");
         }
         if (reactive) {
-            additionalProperties.put(RESPONSE_WRAPPER, "Mono");
+            // The response wrapper when Reactive is enabled must depend on the return type:
+            // Flux<X> when X is an array
+            // Mono<X> otherwise
+            // But there are corner cases when also using response entity.
+            // When reactive is enabled, all this is managed in the mustache templates.
+            additionalProperties.put(RESPONSE_WRAPPER, "");
         }
 
         // Some well-known Spring or Spring-Cloud response wrappers

modules/openapi-generator/src/main/resources/JavaSpring/libraries/spring-http-interface/api.mustache

@@ -57,7 +57,7 @@ public interface {{classname}} {
         accept = "{{{vendorExtensions.x-accepts}}}"{{/vendorExtensions.x-accepts}}{{#vendorExtensions.x-content-type}},
         contentType = "{{{vendorExtensions.x-content-type}}}"{{/vendorExtensions.x-content-type}}
     )
-    {{#responseWrapper}}{{.}}<{{/responseWrapper}}ResponseEntity<{{>returnTypes}}>{{#responseWrapper}}>{{/responseWrapper}} {{operationId}}(
+    {{>responseType}} {{operationId}}(
         {{#allParams}}{{>queryParams}}{{>pathParams}}{{>headerParams}}{{>bodyParams}}{{>formParams}}{{>cookieParams}}{{^-last}},
         {{/-last}}{{/allParams}}
     ){{#unhandledException}} throws Exception{{/unhandledException}};

modules/openapi-generator/src/main/resources/JavaSpring/methodBody.mustache

@@ -50,7 +50,7 @@ Mono<Void> result = Mono.empty();
 {{^examples}}
         exchange.getResponse().setStatusCode({{#returnSuccessCode}}HttpStatus.OK{{/returnSuccessCode}}{{^returnSuccessCode}}HttpStatus.NOT_IMPLEMENTED{{/returnSuccessCode}});
 {{/examples}}
-        return result{{#allParams}}{{#isBodyParam}}{{^isArray}}{{#paramName}}.then({{.}}){{/paramName}}{{/isArray}}{{#isArray}}{{#paramName}}.thenMany({{.}}){{/paramName}}{{/isArray}}{{/isBodyParam}}{{/allParams}}.then(Mono.empty());
+        return result{{#allParams}}{{#isBodyParam}}{{^isArray}}{{#paramName}}.then({{.}}){{/paramName}}{{/isArray}}{{#isArray}}{{#paramName}}.thenMany({{.}}){{/paramName}}{{/isArray}}{{/isBodyParam}}{{/allParams}}{{#isArray}}{{#useResponseEntity}}.then(Mono.empty()){{/useResponseEntity}}{{^useResponseEntity}}.thenMany(Flux.empty()){{/useResponseEntity}}{{/isArray}}{{^isArray}}.then(Mono.empty()){{/isArray}};
 {{/vendorExtensions.x-sse}}
 {{#vendorExtensions.x-sse}}
 exchange.getResponse().setStatusCode({{#returnSuccessCode}}HttpStatus.valueOf({{{statusCode}}}){{/returnSuccessCode}}{{^returnSuccessCode}}HttpStatus.NOT_IMPLEMENTED{{/returnSuccessCode}});

modules/openapi-generator/src/main/resources/JavaSpring/responseType.mustache

@@ -1 +1 @@
-{{^vendorExtensions.x-sse}}{{#responseWrapper}}{{.}}<{{/responseWrapper}}{{#useResponseEntity}}ResponseEntity<{{/useResponseEntity}}{{>returnTypes}}{{#useResponseEntity}}>{{/useResponseEntity}}{{#responseWrapper}}>{{/responseWrapper}}{{/vendorExtensions.x-sse}}{{#vendorExtensions.x-sse}}{{>returnTypes}}{{/vendorExtensions.x-sse}}
+{{^vendorExtensions.x-sse}}{{#reactive}}{{#useResponseEntity}}Mono<ResponseEntity<{{#isArray}}Flux<{{/isArray}}{{>returnTypes}}{{#isArray}}>{{/isArray}}>>{{/useResponseEntity}}{{^useResponseEntity}}{{#isArray}}Flux{{/isArray}}{{^isArray}}Mono{{/isArray}}<{{>returnTypes}}>{{/useResponseEntity}}{{/reactive}}{{^reactive}}{{#responseWrapper}}{{.}}<{{/responseWrapper}}{{#useResponseEntity}}ResponseEntity<{{/useResponseEntity}}{{>returnTypes}}{{#useResponseEntity}}>{{/useResponseEntity}}{{#responseWrapper}}>{{/responseWrapper}}{{/reactive}}{{/vendorExtensions.x-sse}}{{#vendorExtensions.x-sse}}{{#isArray}}Flux{{/isArray}}{{^isArray}}Mono{{/isArray}}<{{>returnTypes}}>{{/vendorExtensions.x-sse}}

modules/openapi-generator/src/main/resources/JavaSpring/returnTypes.mustache

@@ -1 +1 @@
-{{#isMap}}Map<String, {{{returnType}}}>{{/isMap}}{{#isArray}}{{#reactive}}Flux{{/reactive}}{{^reactive}}{{{returnContainer}}}{{/reactive}}<{{{returnType}}}>{{/isArray}}{{^returnContainer}}{{#useResponseEntity}}{{{returnType}}}{{/useResponseEntity}}{{^useResponseEntity}}{{#isDelegate}}{{#isVoid}}{{#responseWrapper}}{{{returnType}}}{{/responseWrapper}}{{^responseWrapper}}void{{/responseWrapper}}{{/isVoid}}{{^isVoid}}{{{returnType}}}{{/isVoid}}{{/isDelegate}}{{^isDelegate}}{{#async}}{{{returnType}}}{{/async}}{{^async}}{{#isVoid}}{{#responseWrapper}}{{{returnType}}}{{/responseWrapper}}{{^responseWrapper}}void{{/responseWrapper}}{{/isVoid}}{{^isVoid}}{{{returnType}}}{{/isVoid}}{{/async}}{{/isDelegate}}{{/useResponseEntity}}{{/returnContainer}}
+{{#isMap}}Map<String, {{{returnType}}}>{{/isMap}}{{#isArray}}{{#reactive}}{{{returnType}}}{{/reactive}}{{^reactive}}{{{returnContainer}}}<{{{returnType}}}>{{/reactive}}{{/isArray}}{{^returnContainer}}{{#useResponseEntity}}{{{returnType}}}{{/useResponseEntity}}{{^useResponseEntity}}{{#isDelegate}}{{#isVoid}}{{#responseWrapper}}{{{returnType}}}{{/responseWrapper}}{{^responseWrapper}}void{{/responseWrapper}}{{/isVoid}}{{^isVoid}}{{{returnType}}}{{/isVoid}}{{/isDelegate}}{{^isDelegate}}{{#async}}{{{returnType}}}{{/async}}{{^async}}{{#isVoid}}{{#responseWrapper}}{{{returnType}}}{{/responseWrapper}}{{^responseWrapper}}void{{/responseWrapper}}{{/isVoid}}{{^isVoid}}{{{returnType}}}{{/isVoid}}{{/async}}{{/isDelegate}}{{/useResponseEntity}}{{/returnContainer}}

modules/openapi-generator/src/test/java/org/openapitools/codegen/java/spring/SpringCodegenTest.java

@@ -541,14 +541,19 @@ public class SpringCodegenTest {
     }
 
     @Test
-    public void springcloudWithAsyncAndJava8HasResponseWrapperCompletableFuture() {
+    public void springcloudWithAsyncAndJava8HasResponseWrapperCompletableFuture() throws IOException {
-        final SpringCodegen codegen = new SpringCodegen();
+        Map<String, Object> additionalProperties = new HashMap<>();
-        codegen.additionalProperties().put(SpringCodegen.ASYNC, true);
+        additionalProperties.put(SpringCodegen.ASYNC, "true");
-        codegen.additionalProperties().put(CodegenConstants.LIBRARY, "spring-cloud");
+        additionalProperties.put(CodegenConstants.LIBRARY, "spring-cloud");
-        codegen.processOpts();
+        additionalProperties.put(CodegenConstants.MODEL_TESTS, "false");
+        additionalProperties.put(CodegenConstants.MODEL_DOCS, "false");
+        additionalProperties.put(CodegenConstants.APIS, "true");
+        additionalProperties.put(CodegenConstants.SUPPORTING_FILES, "false");
 
-        Assert.assertEquals(codegen.additionalProperties().get("jdk8-default-interface"), false);
+        Map<String, File> files = generateFromContract("src/test/resources/3_0/petstore.yaml", SPRING_BOOT, additionalProperties);
-        Assert.assertEquals(codegen.additionalProperties().get(RESPONSE_WRAPPER), "CompletableFuture");
+
+        assertFileContains(files.get("PetApi.java").toPath(), "CompletableFuture<ResponseEntity<Void>> deletePet");
+        assertFileNotContains(files.get("PetApi.java").toPath(), "default CompletableFuture<ResponseEntity<Void>> deletePet");
     }
 
     @Test
@@ -1281,6 +1286,50 @@ public class SpringCodegenTest {
         assertFileNotContains(Paths.get(outputPath + "/src/main/java/org/openapitools/api/SomeApiDelegate.java"), "Mono<DummyRequest>");
     }
 
+    @Test
+    public void reactiveArrayShouldBeWrappedInFluxWithoutMono() throws IOException {
+        Map<String, Object> additionalProperties = new HashMap<>();
+        additionalProperties.put(SpringCodegen.DELEGATE_PATTERN, "false");
+        additionalProperties.put(SpringCodegen.REACTIVE, "true");
+        additionalProperties.put(SpringCodegen.USE_RESPONSE_ENTITY, "false");
+        additionalProperties.put(SpringCodegen.USE_SPRING_BOOT3, "true");
+        additionalProperties.put(CodegenConstants.MODEL_TESTS, "false");
+        additionalProperties.put(CodegenConstants.MODEL_DOCS, "false");
+        additionalProperties.put(CodegenConstants.APIS, "true");
+        additionalProperties.put(CodegenConstants.SUPPORTING_FILES, "false");
+        Map<String, File> files = generateFromContract("src/test/resources/3_0/petstore.yaml", SPRING_BOOT, additionalProperties);
+
+        JavaFileAssert
+            .assertThat(files.get("PetApi.java"))
+                .assertMethod("addPet").hasReturnType("Mono<Pet>")
+            .toFileAssert()
+                .assertMethod("findPetsByStatus").hasReturnType("Flux<Pet>")
+            .toFileAssert()
+                .assertMethod("deletePet").hasReturnType("Mono<Void>");
+    }
+
+    @Test
+    public void reactiveArrayShouldBeWrappedInMonoFluxWhenUsingResponseEntity() throws IOException {
+        Map<String, Object> additionalProperties = new HashMap<>();
+        additionalProperties.put(SpringCodegen.DELEGATE_PATTERN, "false");
+        additionalProperties.put(SpringCodegen.REACTIVE, "true");
+        additionalProperties.put(SpringCodegen.USE_RESPONSE_ENTITY, "true");
+        additionalProperties.put(SpringCodegen.USE_SPRING_BOOT3, "true");
+        additionalProperties.put(CodegenConstants.MODEL_TESTS, "false");
+        additionalProperties.put(CodegenConstants.MODEL_DOCS, "false");
+        additionalProperties.put(CodegenConstants.APIS, "true");
+        additionalProperties.put(CodegenConstants.SUPPORTING_FILES, "false");
+        Map<String, File> files = generateFromContract("src/test/resources/3_0/petstore.yaml", SPRING_BOOT, additionalProperties);
+
+        JavaFileAssert
+            .assertThat(files.get("PetApi.java"))
+                .assertMethod("addPet").hasReturnType("Mono<ResponseEntity<Pet>>")
+            .toFileAssert()
+                .assertMethod("findPetsByStatus").hasReturnType("Mono<ResponseEntity<Flux<Pet>>>")
+            .toFileAssert()
+                .assertMethod("deletePet").hasReturnType("Mono<ResponseEntity<Void>>");
+    }
+
     @Test
     public void shouldGenerateValidCodeForReactiveControllerWithoutParams_issue14907() throws IOException {
         File output = Files.createTempDirectory("test").toFile().getCanonicalFile();

samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/api/PetApi.java

@@ -146,7 +146,7 @@ public interface PetApi {
     )
     @ResponseStatus(HttpStatus.OK)
     
-    default Mono<Flux<Pet>> findPetsByStatus(
+    default Flux<Pet> findPetsByStatus(
         @NotNull @ApiParam(value = "Status values that need to be considered for filter", required = true, allowableValues = "available, pending, sold") @Valid @RequestParam(value = "status", required = true) List<String> status,
         @ApiIgnore final ServerWebExchange exchange
     ) {
@@ -189,7 +189,7 @@ public interface PetApi {
     )
     @ResponseStatus(HttpStatus.OK)
     
-    default Mono<Flux<Pet>> findPetsByTags(
+    default Flux<Pet> findPetsByTags(
         @NotNull @ApiParam(value = "Tags to filter by", required = true) @Valid @RequestParam(value = "tags", required = true) Set<String> tags,
         @ApiIgnore final ServerWebExchange exchange
     ) {

samples/server/petstore/springboot-reactive-noResponseEntity/src/main/java/org/openapitools/api/PetApiDelegate.java

@@ -76,7 +76,7 @@ public interface PetApiDelegate {
      *         or Invalid status value (status code 400)
      * @see PetApi#findPetsByStatus
      */
-    default Mono<Flux<Pet>> findPetsByStatus(List<String> status,
+    default Flux<Pet> findPetsByStatus(List<String> status,
         ServerWebExchange exchange) {
         Mono<Void> result = Mono.empty();
         exchange.getResponse().setStatusCode(HttpStatus.NOT_IMPLEMENTED);
@@ -92,7 +92,7 @@ public interface PetApiDelegate {
                 break;
             }
         }
-        return result.then(Mono.empty());
+        return result.thenMany(Flux.empty());
 
     }
 
@@ -107,7 +107,7 @@ public interface PetApiDelegate {
      * @see PetApi#findPetsByTags
      */
     @Deprecated
-    default Mono<Flux<Pet>> findPetsByTags(Set<String> tags,
+    default Flux<Pet> findPetsByTags(Set<String> tags,
         ServerWebExchange exchange) {
         Mono<Void> result = Mono.empty();
         exchange.getResponse().setStatusCode(HttpStatus.NOT_IMPLEMENTED);
@@ -123,7 +123,7 @@ public interface PetApiDelegate {
                 break;
             }
         }
-        return result.then(Mono.empty());
+        return result.thenMany(Flux.empty());
 
     }