A bit complex for such a simple case, but it took me to implement 5 classes, to extract a body from ClientRequest.
It seems to be too much, and I'm still curious if there is a short solution for the problem. You're welcome to propose another answer to this question, so I could accept it.
Unfortunately, it must be said that the design of ClientRequest, BodyInserters and most of the other stuff from org.springframework.web.reactive.*** has a large room for improvement. At the moment it is just a pile of interfaces with tons of methods per each, and it usually takes a lot of efforts to test code, depending on those classes.
The main goal it to get this method working:
static <T> T extractBody(ClientRequest request, Class<T> clazz) {
InsertionReceiver<T> receiver = InsertionReceiver.forClass(clazz);
return receiver.receiveValue(request.body());
}
Here is the implementation of InsertionReceiver:
import org.springframework.http.ReactiveHttpOutputMessage;
import org.springframework.web.reactive.function.BodyInserter;
public interface InsertionReceiver<T> {
T receiveValue(BodyInserter<?, ? extends ReactiveHttpOutputMessage> bodyInserter);
static <T> InsertionReceiver<T> forClass(Class<T> clazz) {
return new SimpleValueReceiver<>(clazz);
}
}
import java.util.concurrent.atomic.AtomicReference;
import org.springframework.http.ReactiveHttpOutputMessage;
import org.springframework.web.reactive.function.BodyInserter;
class SimpleValueReceiver<T> implements InsertionReceiver<T> {
private static final Object DUMMY = new Object();
private final Class<T> clazz;
private final AtomicReference<Object> reference;
SimpleValueReceiver(Class<T> clazz) {
this.clazz = clazz;
this.reference = new AtomicReference<>(DUMMY);
}
@Override
public T receiveValue(BodyInserter<?, ? extends ReactiveHttpOutputMessage> bodyInserter) {
demandValueFrom(bodyInserter);
return receivedValue();
}
private void demandValueFrom(BodyInserter<?, ? extends ReactiveHttpOutputMessage> bodyInserter) {
var inserter = (BodyInserter<?, ReactiveHttpOutputMessage>) bodyInserter;
inserter.insert(
MinimalHttpOutputMessage.INSTANCE,
new SingleWriterContext(new WriteToConsumer<>(reference::set))
);
}
private T receivedValue() {
Object value = reference.get();
reference.set(DUMMY);
T validatedValue;
if (value == DUMMY) {
throw new RuntimeException("Value was not received, Check your inserter worked properly");
} else if (!clazz.isAssignableFrom(value.getClass())) {
throw new RuntimeException(
"Value has unexpected type ("
+ value.getClass().getTypeName()
+ ") instead of (" + clazz.getTypeName() + ")");
} else {
validatedValue = clazz.cast(value);
}
return validatedValue;
}
}
class WriteToConsumer<T> implements HttpMessageWriter<T> {
private final Consumer<T> consumer;
private final List<MediaType> mediaTypes;
WriteToConsumer(Consumer<T> consumer) {
this.consumer = consumer;
this.mediaTypes = Collections.singletonList(MediaType.ALL);
}
@Override
public List<MediaType> getWritableMediaTypes() {
return mediaTypes;
}
@Override
public boolean canWrite(ResolvableType elementType, MediaType mediaType) {
return true;
}
@Override
public Mono<Void> write(
Publisher<? extends T> inputStream,
ResolvableType elementType,
MediaType mediaType,
ReactiveHttpOutputMessage message,
Map<String, Object> hints
) {
inputStream.subscribe(new OneValueConsumption<>(consumer));
return Mono.empty();
}
}
class MinimalHttpOutputMessage implements ReactiveHttpOutputMessage {
public static MinimalHttpOutputMessage INSTANCE = new MinimalHttpOutputMessage();
private MinimalHttpOutputMessage() {
}
@Override
public HttpHeaders getHeaders() {
return HttpHeaders.EMPTY;
}
// other overridden methods are omitted as they do nothing,
// i.e. return null, false, or have empty bodies
}
class OneValueConsumption<T> implements Subscriber<T> {
private final Consumer<T> consumer;
private int remainedAccepts;
public OneValueConsumption(Consumer<T> consumer) {
this.consumer = Objects.requireNonNull(consumer);
this.remainedAccepts = 1;
}
@Override
public void onSubscribe(Subscription s) {
s.request(1);
}
@Override
public void onNext(T o) {
if (remainedAccepts > 0) {
consumer.accept(o);
remainedAccepts -= 1;
} else {
throw new RuntimeException("No more values can be consumed");
}
}
@Override
public void onError(Throwable t) {
throw new RuntimeException("Single value was not consumed", t);
}
@Override
public void onComplete() {
// nothing
}
}
class SingleWriterContext implements BodyInserter.Context {
private final List<HttpMessageWriter<?>> singleWriterList;
SingleWriterContext(HttpMessageWriter<?> writer) {
this.singleWriterList = List.of(writer);
}
@Override
public List<HttpMessageWriter<?>> messageWriters() {
return singleWriterList;
}
@Override
public Optional<ServerHttpRequest> serverRequest() {
return Optional.empty();
}
@Override
public Map<String, Object> hints() {
return null;
}
}
