I'm building a simple REST API in Kotlin and front-end with React. I'm pretty new to Kotlin and Spring, but I've managed to get a simple service working with Postman. I'm able to return all objects in an SQL table using JpaRepository interface. When I make the call through Postman, my output is as expected (looks like a normal Json object).
However, when I make the call through a standard react fetch the body is produced as a ReadableStream {locked: false}. I did some research on readable streams and they appear to mostly be for images. I tried body.getReader() from https://developer.mozilla.org/en-US/docs/Web/API/Streams_API/Using_readable_streams, but that did not work either.
Here is my Kotlin code:
import org.springframework.web.bind.annotation.*
#RestController
#RequestMapping("/api/catalog")
class ArtworkController (
private val artworkService: ArtworkService
) {
#CrossOrigin
#GetMapping("")
#ResponseBody
fun getData(): MutableList<Artwork> {
// println(artworkService.getArt().javaClass.kotlin)
return artworkService.getArt()
}
}
#Service
class ArtworkService(
private val artworkRepository: ArtworkRepository
){
fun getArt(): MutableList<Artwork> {
return artworkRepository.findAll()
}
}
These are in separate files - just joined them here for brevity.
Any help would be greatly appreciated!
It turns out I was immediately returning a promise and had to set up an async function to handle the request.
const { isLoading, error, data } = useQuery("repoData",
async () => {
const data = await fetch("https://url_here")
.then(function(response) {
return response.json()
}
)
setData(data)
}
For context, this request is wrapped in react-query but works without it as well.
Related
I am working on spring reactive and need to call multiple calls sequentially to other REST API using webclient. The issue is I am able to call multiple calls to other Rest API but response am not able to read without subscribe or block. I can't use subscribe or block due to non reactive programming. Is there any way, i can merge while reading the response and send it as flux.
Below is the piece of code where I am stuck.
private Flux<SeasonsDto> getSeasonsInfo(List<HuntsSeasonsMapping> l2, String seasonsUrl) {
for (HuntsSeasonsMapping s : l2)
{
List<SeasonsJsonDto> list = huntsSeasonsProcessor.appendSeaosonToJson(s.getSeasonsRef());
for (SeasonsJsonDto sjdto:list)
{
Mono<SeasonsDto> mono =new SeasonsAdapter("http://localhost:8087/").callToSeasonsAPI(sjdto.getSeasonsRef());
//Not able to read stream without subscribe an return as Flux object
}
public Mono<SeasonsDto> callToSeasonsAPI(Long long1) {
LOGGER.debug("Seasons API call");
return this.webClient.get().uri("hunts/seasonsInfo/"
+long1).header("X-GoHunt-LoggedIn-User",
"a4d4b427-c716-458b-9bb5-9917b6aa30ff").retrieve().bodyToMono(SeasonsDto.class);
}
Please help to resolve this.
You need to combine the reactive streams using operators such as map, flatMap and concatMap.
private Flux<SeasonsDto> getSeasonsInfo(List<HuntsSeasonsMapping> l2, String seasonsUrl) {
List<Mono<SeasonsDto>> monos = new ArrayList<>();
for (HuntsSeasonsMapping s : l2) {
List<SeasonsJsonDto> list = huntsSeasonsProcessor.appendSeaosonToJson(s.getSeasonsRef());
for (SeasonsJsonDto sjdto:list) {
Mono<SeasonsDto> mono =new SeasonsAdapter("http://localhost:8087/").callToSeasonsAPI(sjdto.getSeasonsRef());
//Not able to read stream without subscribe an return as Flux object
monos.add(mono);
}
}
return Flux.fromIterable(monos).concatMap(mono -> mono);
}
This can further be improved using the steam API, which I suggest you look into, but I didn't want to change too much of your existing code.
I have figured how to do this. I have completely rewrite the code and change in reactive. It means all the for loop has been removed. Below is the code for the same and may be help for others.
public Flux<SeasonsDto> getAllSeasonDetails(String uuid) {
return hunterRepository.findByUuidAndIsPrimaryAndDeleted(uuid, true, false).next().flatMapMany(h1 -> {
return huntsMappingRepository.findByHunterIdAndDeleted(h1.getId(), false).flatMap(k -> {
return huntsMappingRepository.findByHuntReferrenceIdAndDeleted(k.getHuntReferrenceId(), false)
.flatMap(l2 -> {
return huntsSeasonsProcessor.appendSeaosonToJsonFlux(l2.getSeasonsDtl()).flatMap(fs -> {
return seasonsAdapter.callSeasonsAPI(fs.getSeasonsRef(), h1.getId(), uuid).map(k->{
return k;
});
});
});
});
});
}
I am trying to convert a REST service from the Spring 5 Reactive style to an async Kotlin Coroutine style.
I followed several different guides/tutorials on how this should work but I must be doing something wrong.
I get a compile error trying to turn a single object into a Flow, whereas the guides I'm following dont seem to do this at all.
Any pointers or otherwise very appreciated!
Router:
#Bean
fun mainRouter(handler: EobHandler) = coRouter {
GET("/search", handler::search)
GET("/get", handler::get)
}
Handler:
suspend fun search(request: ServerRequest): ServerResponse {
val eobList = service.search()
return ServerResponse.ok().bodyAndAwait(eobList)
}
suspend fun get(request: ServerRequest): ServerResponse
val eob = service.get()
return ServerResponse.ok().bodyAndAwait(eob); // compile error about bodyAndAwait expecting a Flow<T>
}
Service:
override fun search(): Flow<EOB> {
return listOf(EOB()).asFlow()
}
//
override suspend fun get(): EOB? {
return EOB()
}
If curious, here are some of the guides I've based my code on:
https://www.baeldung.com/spring-boot-kotlin-coroutines
https://docs.spring.io/spring/docs/5.2.0.M1/spring-framework-reference/languages.html#how-reactive-translates-to-coroutines
https://medium.com/#hantsy/using-kotlin-coroutines-with-spring-d2784a300bda
I was able to get this to compile by changing
return ServerResponse.ok().bodyAndAwait(eob);
to
return eob?.let { ServerResponse.ok().bodyValueAndAwait(it) } ?: ServerResponse.notFound().buildAndAwait()
guess it's something to do with type-safety of Kotlin - I was not returning a nullable object I think
I'm implementing a server using Ktor, and one of the calls is to get a (potentially large) list of users that will come from a database query. I would like to chunk my response, so my user call looks like this:
fun users() =
flow {
emit("A")
emit("B")
emit("C")
}
Where the emit calls will eventually be replaced with data from a result set. The route looks like this:
route("Users") {
get() {
call.respondTextWriter {
users().collect { write(it) }
flush()
}
}
// other calls, e.g. post(), delete(), etc.
However, both calls to write and flush show a warning: "Inappropriate blocking method call". What am I missing?
Thanks.
Eh, a little digging provided the answer:
private suspend fun <T> flowResponse(writer: Writer, flow: Flow<T>) {
val gson = Gson()
flow.collect { data ->
withContext(Dispatchers.IO) {
writer.write(gson.toJson(data))
}
}
withContext(Dispatchers.IO) { writer.flush() }
}
And then:
get() {
call.respondTextWriter {
flowResponse(this, Users.all())
}
}
Slight change from the question, as my Users.all() call returns a User object that then gets converted to JSON. Perhaps there is a way to simply stream the objects and let the content negotiator do the translation, but I haven't gotten there yet.
I have a service that requests data from a get method, I'd like to map the response to an object storing some Ids and use those Ids to make other http requests.
I was told this isn't usually done in a callback manner, I looked at this How do I return the response from an asynchronous call? but I don't think it's the usual way to implement services, any hints are very appreciated.
Tried adding in onInit/constructor method in angular to be sure the object was filled before other methods were called without success.
#Injectable ()
export class ContactService {
storeIds;
getIds(callback: Function) {
this.http.get<any>(IdsUrl, Config.options).subscribe(res => {
callback(response);
});
getIds(res => {
this.storeIds = {
profileId: res.profile,
refIds: res.refIds
}
}
)
// this.storeIds returns undefined as it's an async call
this.http.post<any>(WebserviceUrl + this.storeIds.profileId , data, headers )
// .....Many other web services that relay on this Ids
}
Just create another service called StoreIdsService. Update the response you get from your first api call 'getIds' in the StoreIdsService. The idea is to have StoreIdsService as singleton service to keep state of your storeIds. You can inject StoreIdsService in anywhere component you want to get the storeIds.
Its one of manyways to share data in angular between components.
Please refer to this answer someone has posted.
How do I share data between components in Angular 2?
You can simply assign the service response to the storeIds property inside the subscribe method. and call the subsequent services inside it if you need.
#Injectable ()
export class ContactService {
storeIds;
getIds() {
this.http.get<any>(IdsUrl, Config.options).subscribe(res => {
this.storeIds = {
profileId: response.profile,
refIds: response.refIds
}
this.otherapicall1();
this.otherapicall2();
});
}
We are working with spring boot 2.0.0.BUILD_SNAPSHOT and spring boot webflux 5.0.0 and currently we cant transfer a flux to a client on request.
Currently I am creating the flux from an iterator:
public Flux<ItemIgnite> getAllFlux() {
Iterator<Cache.Entry<String, ItemIgnite>> iterator = this.getAllIterator();
return Flux.create(flux -> {
while(iterator.hasNext()) {
flux.next(iterator.next().getValue());
}
});
}
And on request I am simply doing:
#RequestMapping(value="/all", method=RequestMethod.GET, produces="application/json")
public Flux<ItemIgnite> getAllFlux() {
return this.provider.getAllFlux();
}
When I now locally call localhost:8080/all after 10 seconds I get a 503 status code. Also as at client when I request /all using the WebClient:
public Flux<ItemIgnite> getAllPoducts(){
WebClient webClient = WebClient.create("http://localhost:8080");
Flux<ItemIgnite> f = webClient.get().uri("/all").accept(MediaType.ALL).exchange().flatMapMany(cr -> cr.bodyToFlux(ItemIgnite.class));
f.subscribe(System.out::println);
return f;
}
Nothing happens. No data is transferred.
When I do the following instead:
public Flux<List<ItemIgnite>> getAllFluxMono() {
return Flux.just(this.getAllList());
}
and
#RequestMapping(value="/allMono", method=RequestMethod.GET, produces="application/json")
public Flux<List<ItemIgnite>> getAllFluxMono() {
return this.provider.getAllFluxMono();
}
It is working. I guess its because all data is already finished loading and just transferred to the client as it usually would transfer data without using a flux.
What do I have to change to get the flux streaming the data to the web client which requests those data?
EDIT
I have data inside an ignite cache. So my getAllIterator is loading the data from the ignite cache:
public Iterator<Cache.Entry<String, ItemIgnite>> getAllIterator() {
return this.igniteCache.iterator();
}
EDIT
adding flux.complete() like #Simon Baslé suggested:
public Flux<ItemIgnite> getAllFlux() {
Iterator<Cache.Entry<String, ItemIgnite>> iterator = this.getAllIterator();
return Flux.create(flux -> {
while(iterator.hasNext()) {
flux.next(iterator.next().getValue());
}
flux.complete(); // see here
});
}
Solves the 503 problem in the browser. But it does not solve the problem with the WebClient. There is still no data transferred.
EDIT 3
using publishOn with Schedulers.parallel():
public Flux<ItemIgnite> getAllFlux() {
Iterator<Cache.Entry<String, ItemIgnite>> iterator = this.getAllIterator();
return Flux.<ItemIgnite>create(flux -> {
while(iterator.hasNext()) {
flux.next(iterator.next().getValue());
}
flux.complete();
}).publishOn(Schedulers.parallel());
}
Does not change the result.
Here I post you what the WebClient receives:
value :[Item ID: null, Product Name: null, Product Group: null]
complete
So it seems like he is getting One item (out of over 35.000) and the values are null and he is finishing after.
One thing that jumps out is that you never call flux.complete() in your create.
But there's actually a factory operator that is tailored to transform an Iterable to a Flux, so you could just do Flux.fromIterable(this)
Edit: in case your Iterator is hiding complexity like a DB request (or any blocking I/O), be advised this spells trouble: anything blocking in a reactive chain, if not isolated on a dedicated execution context using publishOn, has the potential to block not only the entire chain but other reactive processes has well (as threads can and will be used by multiple reactive processes).
Neither create nor fromIterable do anything in particular to protect from blocking sources. I think you are facing that kind of issue, judging from the hang you get with the WebClient.
The problem was my Object ItemIgnite which I transfer. The system Flux seems not to be able to handle this. Because If I change my original code to the following:
public Flux<String> getAllFlux() {
Iterator<Cache.Entry<String, ItemIgnite>> iterator = this.getAllIterator();
return Flux.create(flux -> {
while(iterator.hasNext()) {
flux.next(iterator.next().getValue().toString());
}
});
}
Everything is working fine. Without publishOn and without flux.complete(). Maybe someone has an idea why this is working.