CODEWITHSUNDEEP
javaspring-bootproject-reactor
youngDev
youngDev

Reputation: 339

How to combine List<Mono<String>> in a big String?

I have created a List of String Monos List<Mono<String>> myList. And now I need to concatenate them in a big string.

When I initialize a StringBuilder and update it asyncronously, the empty line maybe returned.

//method body....

StringBuilder builder = new StringBuilder();

myList.forEach {
    mono ->
    mono.map{ str -> builder.append(str)}
}

return builder.toString() //<- is ""

How can I make the builder wait for the monos?

Upvotes: 2

Views: 3045

Answers (1)

mslowiak
mslowiak

Reputation: 1838

The best way is to convert List of Monos to Flux and then reduce your flux to have one string which contains all your substrings. Then you have Mono that you can use still in async way. (You should always work on Mono/Flux if you want to keep async paradigm with project reactor)

Example:

    List<Mono<String>> listOfMonosWithString = Arrays.asList(Mono.just("a"), Mono.just("b"), Mono.just("c"));
    Flux<String> mergedMonos = Flux.fromIterable(listOfMonosWithString)
            .flatMapSequential(Function.identity());

    mergedMonos
            .reduce(String::concat)
            .doOnNext(System.out::println)
            .subscribe();

Upvotes: 2

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