Using Block() on Mono Always Fails
I Have a Function That Works on a Single Element: Mono myFunction(String Arg) { // Do Shiz Return Result; } Now, I Am Trying to Reuse the Above Method to Do...
I have a function that works on a single element:
Mono<Foo> myFunction(String arg) {
// do shiz
return result;
}
Now, I am trying to reuse the above method to do the same, but for a list of args:
Mono<List<Foo>> myNewFunction(List<String> args) {
Flux.fromIterable(args)
.map(currentArg -> myFunction(currentArg))
.map(Mono::block)
.collectList();
}
But it always fails with the same error:
ava.lang.IllegalStateException: block()/blockFirst()/blockLast() are blocking, which is not supported in thread reactor-http-nio-3
...
Error has been observed at the following site(s):
|_ checkpoint ⇢ Handler com.xxx.yyy.zzz.Controller#foo(InputRequest) [DispatcherHandler]
|_ checkpoint ⇢ org.springframework.boot.actuate.metrics.web.reactive.server.MetricsWebFilter [DefaultWebFilterChain]
|_ checkpoint ⇢ HTTP POST "/v1/my/end/point" [ExceptionHandlingWebHandler]
(A controller is calling the myNewFunction)
I have verified that myFunction works when I call it directly from the controller. But when I go through myNewFunction, it fails.
How do I debug this and fix this? I can't tell what the error is. Thanks
1 Answer
First, Flux is an asynchronous sequence of 0-N items, while Mono end with 0-1 result, so your controller shoud return Flux<Foo>:
Flux<Foo> myNewFunction(List<String> args) {
return Flux.fromIterable(args)
// if myFunction returns Mono, use flatMap instead of map.
.flatMap(currentArg -> myFunction(currentArg));
}
If you want return Mono<List<Foo>> instead of Flux<Foo>, use collectList:
Mono<List<Foo>> myNewFunction(List<String> args) {
return Flux.fromIterable(args)
.flatMap(currentArg -> myFunction(currentArg))
.collectList();
}
Second, blocking operation should not used in non-blocking thread, which cause the error.
David Miller brings 15 years of experience in global economics, personal finance strategy, and market dynamics. He specializes in turning complex economic trends into actionable insights for everyday readers.
