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Spring boot rest endpoint returning null with fetch request

I have already created Rest Endpoint in Java spring boot. It returns appropriate response when I request it via Postman. But when I use react fetch it does not show any response in browser if return is Json.
Spring boot controller:
#RestController
#RequestMapping(path = "/v1/test")
#AllArgsConstructor(onConstructor_ = {#Autowired})
public class TestController {
...
}
Below endpoint is returning appropriate response.
#GetMapping(value = "/helloWorld", produces = MediaType.APPLICATION_JSON_VALUE)
#ResponseStatus(HttpStatus.OK)
public String getHelloWorld() {
return "Hello, World1!";
}
But when I try to hit below endpoint it returns null when I make fetch request. But it returns appropriate response when I hit it via postman.
#GetMapping(value = "/testEndpoint", produces = MediaType.APPLICATION_JSON_VALUE)
#ResponseStatus(HttpStatus.OK)
public String returnTestResponse() {
HashMap<String, Object> map = new HashMap<>();
map.put("key1", "value1");
map.put("results", "value2");
return "{\"a\":1, \"b\":\"foo\"}";
}
Also tried returning POJO object. But still no response.
#GetMapping(value = "/testModel", produces = MediaType.APPLICATION_JSON_VALUE)
#ResponseStatus(HttpStatus.OK)
public SearchResultsModel testModel() {
this.myService.getSearchResult();
}
React fetch call:
await fetch(ALL_ARTICLES_ENDPOINT, {
mode: 'no-cors',
method: 'GET',
redirect: 'follow',
headers: {
'Content-Type': 'application/json',
'Accept': 'application/json',
},
}).then(response => {
console.log(response);
})
.then(data => {
console.log('Success:', data);
}).catch((error) => {
console.error('Error:', error);
});

Postman have couple hidden headers which are being sent with all requests.
Check Hide auto-generated headers
What you are missing in react call is is Accept header with application/json value
EDIT:
Just saw that you are returning string as json. You need to wrap it in POJO object and return it in returnTestResponse class
SECOND EDIT:
This will work. Try to implement your POJO
#GetMapping(value = "/testEndpoint", produces = MediaType.APPLICATION_JSON_VALUE)
#ResponseStatus(HttpStatus.OK)
public YourObject returnTestResponse() {
HashMap<String, Object> map = new HashMap<>();
map.put("key1", "value1");
map.put("results", "value2");
return new YourObject(map);
}

Issue was caused by adding mode: 'no-cors' option in fetch request. This option helped me to get rid of cors error but it means that in return I won't be able to see body and headers in chrome.
To resolve the issue I removed mode: 'no-cors' and added #CrossOrigin annotation on my spring boot controller.

WebFlux Swagger (Open API) integraton - Post Request sample

I have integrated Swagger (OpenAPI) with Spring Webflux as mentioned here: https://springdoc.org/#spring-weblfuxwebmvcfn-with-functional-endpoints using RouterOperation. The integration works fine and is accessible at /swagger-ui.html
However, for POST APIs, I am not seeing the "Request" sample when I click on "Try it out" button. My Post API accepts a Json as Request Body.
How do I configure this ? Can that be done via Annotations along with RouterOperation or something else ?
Edit: Below is my Router class code:
#Configuration
public class MyRouter {
#RouterOperations({
#RouterOperation(path = "/data", beanClass = MyHandler.class, beanMethod = "getData"),
#RouterOperation(path = "/allData", beanClass = MyHandler.class, beanMethod = "getAllData") })
#Bean
public RouterFunction<ServerResponse> route(MyHandler MyHandler) {
return RouterFunctions
.route(RequestPredicates.POST("/data").and(RequestPredicates.accept(MediaType.APPLICATION_JSON)), MyHandler::getData)
.andRoute(RequestPredicates.GET("/allData").and(RequestPredicates.accept(MediaType.APPLICATION_JSON)), MyHandler::getAllData);
}
}
Upon adding RouterOperations annotation I can see the swagger-ui showing both the GET and POST APIs correctly but not the request schema sample.
I also came across yaml / json file to describe this. But I am not getting where to put this file in my application so that swagger-ui uses it.

Finally found it
Using #Operation and #Schema, can define the class that is required as input in request body. This will be shown as sample json structure in Swagger-ui. No other configuration required.
#RouterOperations({
#RouterOperation(
path = "/data", beanClass = MyHandler.class, beanMethod = "getData",
operation = #Operation(
operationId = "opGetData",
requestBody = #RequestBody(required = true, description = "Enter Request body as Json Object",
content = #Content(
schema = #Schema(implementation = ApiRequestBody.class))))),
#RouterOperation(path = "/allData", beanClass = MyHandler.class, beanMethod = "getAllData")})
#Bean
public RouterFunction<ServerResponse> route(MyHandler myHandler) {
return RouterFunctions
.route(RequestPredicates.POST("/data").and(RequestPredicates.accept(MediaType.APPLICATION_JSON)), myHandler::getData)
.andRoute(RequestPredicates.GET("/allData").and(RequestPredicates.accept(MediaType.APPLICATION_JSON)), myHandler::getAllData);
}

How to define different response models for different status codes in openApi / springfox-swagger2

Given the following REST method with springfox-swagger2 annotations:
#GetMapping(value = "/access", produces = MediaType.APPLICATION_JSON_VALUE)
#ApiOperation(value = "check access allowed")
#ApiResponses({
#ApiResponse(code = 200, message = "okay, there you go", response = AccessResponse.class),
#ApiResponse(code = 204, message = "I got nothing for you", response = Void.class)
})
public ResponseEntity<AccessResponse> access() {
if (!isAccessEnabled()) {
return ResponseEntity.status(HttpStatus.NO_CONTENT).build();
}
AccessResponse response = new AccessResponse("some data");
return ResponseEntity.ok(response);
}
Notice that there are two states that this method can return:
a response of type AccessResponse
a http 204 - no content response
I want to generate a swagger api documentation that reflects the different response models (AccessResponse vs. Void). Inside the #ApiResponse Annotation I explicitly tell springfox-swagger2 to use different models for each state.
Unfortunately the generated swagger api doc json refers only to the AccessResponse model for both http 200 and 204:
"responses":{
"200":{
"description":"okay, there you go",
"schema":{"$ref":"#/definitions/AccessResponse"}
},
"204":{
"description":"I got nothing for you",
"schema":{"$ref":"#/definitions/AccessResponse"}
}
}
Am I missing something? Is there a way to tell swagger to render two different models for each HTTP/ok status code?

I've changed the return type of the method - removing the generic type:
public ResponseEntity access()
which results in a better (but not perfect) model description:
"204":{
"description": "I got nothing for you",
"schema":{"type":"object"}
}
Swagger UI renders this to
I like that it displays the empty body now. However, the statusCode is a bit irritating.

SpringBoot – add Cache Control Headers in Rest methods

I have a basic SpringBoot 2.0.5.RELEASE app. Using Spring Initializer, JPA, embedded Tomcat, Thymeleaf template engine, and package as an executable JAR
I have created this Rest method:
#GetMapping(path = "/users/notifications", consumes = "application/json", produces = "application/json")
public ResponseEntity<List<UserNotification>> userNotifications(
#RequestHeader(value = "Authorization") String authHeader) {
User user = authUserOnPath("/users/notifications", authHeader);
List<UserNotification> menuAlertNotifications = menuService
.getLast365DaysNotificationsByUser(user);
return ResponseEntity.ok(menuAlertNotifications)
.cacheControl(CacheControl.maxAge(60, TimeUnit.SECONDS));;
}
and I want to add a Cache Control Headers, but I don't know how...
I got a compilation error:
Multiple markers at this line
- The method cacheControl(CacheControl) is undefined for the type
ResponseEntity<List<UserNotification>>
- CacheControl
- cacheControl
I also add this property in application.properties
security.headers.cache=false

When you use ResponseEntity.ok(T body) the return type is ResponseEntity<T> as it is a shortcut method to add data to the body part of the ResponseEntity.
You need the builder object that is created via ResponseEntity.ok() with no param which returns a Builder object. You then add your data yourself on via the body method.
So your code should be like this
#GetMapping(path = "/users/notifications", consumes = "application/json", produces = "application/json")
public ResponseEntity<List<UserNotification>> userNotifications(
#RequestHeader(value = "Authorization") String authHeader) {
User user = authUserOnPath("/users/notifications", authHeader);
List<UserNotification> menuAlertNotifications = menuService
.getLast365DaysNotificationsByUser(user);
return ResponseEntity.ok().cacheControl(CacheControl.maxAge(60, TimeUnit.SECONDS)).body(menuAlertNotifications);
}

API call with Java + STS returning "Content type 'application/octet-stream' not supported"

I am working on part of an API, which requires making a call to another external API to retrieve data for one of its functions. The call was returning an HTTP 500 error, with description "Content type 'application/octet-stream' not supported." The call is expected to return a type of 'application/json."
I found that this is because the response received doesn't explicitly specify a content type in its header, even though its content is formatted as JSON, so my API defaulted to assuming it was an octet stream.
The problem is, I'm not sure how to adjust for this. How would I get my API to treat the data it receives from the other API as an application/json even if the other API doesn't specify a content type? Changing the other API to include a contenttype attribute in its response is infeasible.
Code:
The API class:
#RestController
#RequestMapping(path={Constants.API_DISPATCH_PROFILE_CONTEXT_PATH},produces = {MediaType.APPLICATION_JSON_VALUE})
public class GetProfileApi {
#Autowired
private GetProfile GetProfile;
#GetMapping(path = {"/{id}"})
public Mono<GetProfileResponse> getProfile(#Valid #PathVariable String id){
return GetProfile.getDispatchProfile(id);
}
The service calling the external API:
#Autowired
private RestClient restClient;
#Value("${dispatch.api.get_profile}")
private String getDispatchProfileUrl;
#Override
public Mono<GetProfileResponse> getDispatchProfile(String id) {
return Mono.just(id)
.flatMap(aLong -> {
MultiValueMap<String, String> headers = new HttpHeaders();
headers.add(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE);
return restClient.get(getDispatchProfileUrl, headers);
}).flatMap(clientResponse -> {
HttpStatus status = clientResponse.statusCode();
log.info("HTTP Status : {}", status.value());
return clientResponse.bodyToMono(GetProfileClientResponse.class);
// the code does not get past the above line before returning the error
}).map(GetProfileClientResponse -> {
log.debug("Response : {}",GetProfileClientResponse);
String id = GetProfileClientResponse.getId();
log.info("SubscriberResponse Code : {}",id);
return GetProfileResponse.builder()
// builder call to be completed later
.build();
});
}
The GET method for the RestClient:
public <T> Mono<ClientResponse> get(String baseURL, MultiValueMap<String,String> headers){
log.info("Executing REST GET method for URL : {}",baseURL);
WebClient client = WebClient.builder()
.baseUrl(baseURL)
.defaultHeaders(httpHeaders -> httpHeaders.addAll(headers))
.build();
return client.get()
.exchange();
}
One solution I had attempted was setting produces= {MediaType.APPLICATION_JSON_VALUE} in the #RequestMapping of the API to produces= {MediaType.APPLICATION_OCTET_STREAM_VALUE}, but this caused a different error, HTTP 406 Not Acceptable. I found that the server could not give the client the data in a representation that was requested, but I could not figure out how to correct it.
How would I be able to treat the response as JSON successfully even though it does not come with a content type?
Hopefully I have framed my question well enough, I've kinda been thrust into this and I'm still trying to figure out what's going on.

Are u using jackson library or jaxb library for marshalling/unmarshalling?
Try annotating Mono entity class with #XmlRootElement and see what happens.