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How to validate Exception in spring-webflux WebTestClient tests?

How can I validate the actual Exception in a spring-webflux test?
The following worked in the old spring-web environment, but migrating to netty and spring-webflux, the MvcResult cannot be resolved anymore (NullPointerException):
#SpringBootTest
#AutoConfigureWebTestClient
public class ApiTest {
#Test
public void test() throws Exception {
webTestClient.get()
.uri("/api?test=123")
.exchange()
.expectStatus().isBadRequest()
.expectBody().consumeWith(rsp -> {
//throws NPE
Exception ex = ((MvcResult) rsp.getMockServerResult()).getResolvedException();
assertTrue(ex instanceof ResponseStatusException);
});
}
}
#RestController
public class ApiController {
#PostMapping("/api")
public String test(#RequestParam String test) {
if (test.matches("[0-9]+"))
throw new ResponseStatusException(HttpStatus.BadRequest, "Prohibited characters");
}
}
How could I still validate the real exception class?

The main purpose of the WebTestClient is to test endpoints using fluent API to verify responses. There is no magic deserialization or error handling happening but you can get access to the raw responses (status, headers, body).
In your example you will not get MvcResult or ResponseStatusException but you could get access to the raw body using rsp.getResponseBody() that would look like
{
"timestamp": "2022-05-17T17:57:07.041+00:00",
"path": "/api",
"status": 400,
"error": "Bad Request",
"requestId": "4fa648d"
}
You could use expectBody().consumeWith(rsp -> { ... }) to get access to the request and response or expectBody(String.class).value(body -> { ... })to get just body. As an alternative use some fluent API to validate result JSON.expectBody().json()or.expectBody().jsonPath()` to check specific fields only.
In addition you could still deserialize body explicitly using .expectBody(Response.class).value(body -> {...}).

Java Spring Boot Webflux - Mono response when there is no http body, but just http status

Small question regarding Spring Boot Webflux 2.5.0 and how to deal with a http response without body.
By "without body" I mean:
For instance, a web application I consume the rest API and have no control returns:
HTTP status code 200
HTTP body {"foo": "bar"}
With Spring Webflux, we can easily write something like:
public Mono<FooBar> sendRequest(SomeRequest someRequest) {
return webClient.mutate()
.baseUrl("https://third-party-rest-api.com:443")
.build()
.post()
.uri(/someroute)
.body(BodyInserters.fromValue(someRequest))
.retrieve().bodyToMono(FooBar.class);
}
public class FooBar {
private String foo;
//getter setters
}
In order to get the POJO corresponding to the http body.
Now, another third party API I am consuming only return HTTP 200 as status response.
I would like to emphasize, there is no HTTP body. It is not the empty JSON {}.
Hence, I am a bit lost, and do not know what to put here. Especially with the goal of avoiding the mono empty.
public Mono<WhatToPutHerePlease> sendRequest(SomeRequest someRequest) {
return webClient.mutate()
.baseUrl("https://third-party-rest-api.com:443")
.build()
.post()
.uri(/someroute-with-no-http-body-response)
.body(BodyInserters.fromValue(someRequest))
.retrieve()
.bodyToMono(WhatToPutHerePlease.class);
}
Any help please?
Thank you

Hence, I am a bit lost, and do not know what to put here.
The response is empty, so there's nothing for your webclient to parse and return a value. The resulting Mono is thus always going to be empty, whatever generic type you use.
We have a special type that essentially says "this will always be empty" - Void (note the capital V.) So if you want to return an empty Mono, keeping the rest of the code the same, that's the type you should use.
Alternatively, if you don't want to return an empty publisher, then you might consider using .retrieve().toBodiLessEntity() instead of .retrieve().bodyToMono() - this will return a Mono<ResponseEntity<Void>>. The resulting body will obviously still be empty, but the response entity returned will enable you to extract information such as the response code & header information, should that be useful.

toBodylessEntity() seems to suit your needs:
It returns a Mono<ResponseBody<Void>>.
With a (void rest) controller like:
#RestController
#SpringBootApplication
public class Demo {
public static void main(String[] args) {
SpringApplication.run(Demo.class, args);
// ...
}
#GetMapping("/")
public void empty() {
}
}
and a:
public class ReactiveClient {
Mono<ResponseEntity<Void>> mono = WebClient.create("http://localhost:8080")
.get()
.retrieve()
.toBodilessEntity();
// blocking/synchronous
public ResponseEntity<Void> get() {
return mono.block();
}
}
We can:
ReactiveClient reactiveClient = new ReactiveClient();
System.out.println(reactiveClient.get()); // or something else

Jersey Test Framework - define default error response for all unknown paths in grizzly

To test our API that connects to the facebook graph API we use a mock server setup based on Jersey Test Framework and grizzly:
#Path("/" + PostRest.RESOURCE)
#Produces("application/json")
public class PostRest {
public static final String RESOURCE = "111_222";
#GET
public Response getPost(#QueryParam("access_token") String access_token) {
if (access_token != VALID_TOKEN) {
return Response.status(400).entity(createErrorJson()).build();
}
return Response.status(200).entity(createSomeJsonString()).build();
}
Now while I can react to an invalid or missing access_token with the correct error response, I also want to test that my API reacts correctly when trying to access an unkown resource at facebook ie an unkown path.
Right now I get a 404 from my grizzly obviously, if I try to access say "/111_2", but facebook seems to catch that error and wrap it inside a Json response, containing the string "false" with status 200.
So... How do I set up the Test Framework to return
Response.status(200).entity("false").build();
every time it is called for an known path?
Basic example:
#ContextConfiguration({ "classpath:context-test.xml" })
#RunWith(SpringJUnit4ClassRunner.class)
public class SomeTest extends JerseyTest {
#Inject
private SomeConnection connection;
private String unkownId = "something";
public SomeTest() throws Exception {
super("jsonp", "", "com.packagename.something");
}
#Test(expected = NotFoundException.class)
public void testUnkownObjectResponse() throws NotFoundException {
// here it should NOT result in a 404 but a JSON wrapped error response
// which will be handled by the Connection class and
// result in a custom exception
connection.getObject(unkownId);
}
Or maybe I can set up grizzly to behave as desired..?!
Thanks!

Obviously facebook has it own service to intercept errors. Same thing should be done in your code. Just expose you own test service that intercepts all request
#Path("/test/errorTrap")
public class ErrorTrapService{
....
}
This service will produce any response you want. So any un-existing pages like http://mytest/test/errorTrap/111_2 will be intercepted by test service and produce expected response for you

How can I override the decisions made during JAX-RS Content Negotiation?

I'm using RESTEasy 2.2.1.GA as my JAX-RS implementation to create a client to connect to a third party service provider. (Education.com's REST API if it matters)
To make sure I haven't missed an important implementation detail here are code samples:
Service Interface
#Path("/")
public interface SchoolSearch {
#GET
#Produces({MediaType.APPLICATION_XML})
Collection<SchoolType> getSchoolsByZipCode(#QueryParam("postalcode") int postalCode);
}
Calling Class
public class SimpleSchoolSearch {
public static final String SITE_URL = "http://api.education.com/service/service.php?f=schoolSearch&key=****&sn=sf&v=4";
SchoolSearch service = ProxyFactory.create(SchoolSearch.class, SITE_URL);
public Collection<SchoolType> getSchools() throws Exception {
Collection<SchoolType> schools = new ArrayList<SchoolType>();
Collection<SchoolType> response = service.getSchoolsByZipCode(35803);
schools.addAll(response);
return schools;
}
}
After setting up tests to make this call, I execute and see the following exception being thrown.
org.jboss.resteasy.plugins.providers.jaxb.JAXBUnmarshalException: Unable to find JAXBContext for media type: text/html;charset="UTF-8"
From reading the RESTEasy/JAX-RS documentation, as I understand it, when the response is returned to the client, prior to the unmarshaling of the data, a determination is made (Content Negotiation??) about which mechanism to use for unmarshalling. (I think we're talking about a MessageBodyReader here but I'm unsure.) From looking at the body of the response, I see that what is returned is properly formatted XML, but the content negotiation (via HTTP header content-type is indeed text/html;charset ="UTF-8") is not allowing the text to be parsed by JAXB.
I think that the implementation is behaving correctly, and it is the service that is in error, however, I don't control the service, but would still like to consume it.
So that being said:
Am I correct in my understanding of why the exception is thrown?
How do I work around it?
Is there a simple one line annotation that can force JAXB to unmarshal the data, or will I need to implement a custom MessageBodyReader? (If that is even the correct class to implement).
Thanks!
Follow Up:
I just wanted to post the few changes I made to Eiden's answer. I created a ClientExecutionInterceptor using his code and the information available at Resteasy ClientExecutionInterceptor documentation. My final class looks like
#Provider
#ClientInterceptor
public class SimpleInterceptor implements ClientExecutionInterceptor {
#Override
public ClientResponse execute(ClientExecutionContext ctx) throws Exception {
final ClientResponse response = ctx.proceed();
response.getHeaders().putSingle(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_XML);
return response;
}
}
The big difference is the addition of the #Provider and #ClientExecutionInterceptor annotations. This should insure that the interceptor is properly registered.
Also, just for completeness, I registered the Interceptor slightly differently for my tests. I used:
providerFactory.registerProvider(SimpleInterceptor.class);

I'm sure there are several solutions to this problem, but I can only think of one.
Try so set the content-type using a ClientExecutionInterceptor:
public class Interceptor implements ClientExecutionInterceptor {
#Override
public ClientResponse<?> execute(ClientExecutionContext ctx) throws Exception {
final ClientResponse<?> response = ctx.proceed();
response
.getHeaders()
.putSingle(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_XML);
return response;
}
}
public void getSchools() throws Exception {
ResteasyProviderFactory.getInstance()
.getClientExecutionInterceptorRegistry()
.register( new Interceptor() );
SchoolSearch service =
ProxyFactory.create(SchoolSearch.class, SITE_URL);
}

I dont know about any such annotation, others might do, but a workaround is to create a local proxy. Create a controller, that passes all parameters to education.com using a
java.Net.URL.get()
return the answer that you received, but modify the header. Then connect your client to the local proxy controller.

Changing content type in jax-rs REST service

Forgive me, but I may not be familiar with all the lingo necessary to ask this question properly.
I'm working on a fairly simple REST web service in Java using the org.apache.cxf.jaxrs.ext implementation of jax-rs. The method header is like this:
#GET
#Path("json/{fullAlias}")
#Produces({"application/json"})
public String json(#PathParam("fullAlias") String fullAlias, #Context MessageContext req)
where MessageContext is org.apache.cxf.jaxrs.ext.MessageContext.
There are two things I'm trying to accomplish that I can't seem to figure out:
Change the content-type if certain conditions are met (e.g. for an error)
Change the status code of the response
I've tried using changing the response by accessing it through the MessageContext:
HttpServletResponse response = req.getHttpServletResponse();
response.setContentType("text/plain")
response.setStatus("HttpServletResponse.SC_BAD_REQUEST);
But these changes have no bearing on the response sent; with or without the #Produces annotation, setting the content type inside the method doesn't affect the actual content type (With the annotation, it of course returns "application/json", without it defaults to "text/html").
I am returning a simple String as the body. I've entertained trying to return a javax.ws.rs.core.Response object to do what I want, but I don't know much about it.
How would I change the content type and/or the status codes from inside this method?

One approach is to throw a WebApplicationException, as described by Pace, which will work if you are looking to specifically handle an error condition. If you are looking to be able to change your content at any time for any reason, then you will want to take a look at returning a Response as the result of your service method rather than a String. Returning a Response gives you the greatest amount of control over how your service responds to the client request (it does require more code than returning a simple string).
Here is an example of how you would can make use of the Response object:
#GET
#Path("json/{fullAlias}")
public Response json(#PathParam("fullAlias") String fullAlias, #Context MessageContext req) {
...
if (success) {
ResponseBuilder rBuild = Response.ok(responseData, MediaType.APPLICATION_JSON);
return rBuild.build();
}
else {
ResponseBuilder rBuild = Response.status(Response.Status.BAD_REQUEST);
return rBuild.type(MediaType.TEXT_PLAIN)
.entity("error message")
.build();
}
}

I'm not sure if it's the best approach but I've done the following to solve your question #1.
public WebApplicationException createStatusException(String statusMessage) {
ResponseBuilder rb = Response.noContent();
rb = rb.type(MediaType.TEXT_PLAIN);
rb = rb.status(Status.BAD_REQUEST);
rb = rb.entity(statusMessage);
return new WebApplicationException(rb.build());
}
EDIT: I then threw the resulting WebApplicationException.

You can write your own Response Filter to change the content-type header.
#Provider
public class MimeAddingFilter implements ContainerResponseFilter {
#Override
public void filter(ContainerRequestContext requestContext, ContainerResponseContext responseContext)
throws IOException {
responseContext.getHeaders().add("Content-Type", "image/png");
}
}
This filter will add the "image/png" content-type header. You can also change or remove headers in JAX-RS response filters.