[FIXED] How to convert List<String> into a Mono<List>

Issue

i'm trying to convert this method to an a reactive method

@GetMapping(RestConstants.BASE_PATH_AUDIENCE + "/link")
public List<String> users () {
    List<String> list= new ArrayList<>();
    MongoCollection mongoCollection = mongoTemplate.getCollection("collection");
    DistinctIterable distinctIterable = mongoCollection.distinct("user_name", String.class);
    MongoCursor mongoCursor = distinctIterable.iterator();
    while (mongoCursor.hasNext()){
        String user = (String)mongoCursor.next();
        creatorsList.add(user);
    }
    return list;
}

I Have something like this but i don't know how to conver the ArrayList to return an Mono<List>

@GetMapping(RestConstants.BASE_PATH_AUDIENCE + "/link")
public Mono<List<String>> usersReactive () {
    List<Mono<String>> list= new ArrayList<List>();
    MongoCollection mongoCollection = mongoTemplate.getCollection("collection");
    DistinctIterable distinctIterable = mongoCollection.distinct("user_name", String.class);
    MongoCursor mongoCursor = distinctIterable.iterator();
    while (mongoCursor.hasNext()){
        String user = (String)mongoCursor.next();
        list.add(user);
    }

    return list;
}

Solution

If you really want a Mono, then just wrap the value that you want to transport in it:

return Mono.just(creatorsList);

But I doubt you really want to return a list in a Mono. Usually, reactive endpoints returning a number of items would return a Flux

return Flux.fromIterable(creatorsList);

But since your MongoCursor is already iterable (you use its iterator in an enhanced for-loop), you can stream the cursor directly to the flux. This saves you from collecting all items into a list first.

return Flux.fromIterable(cursor);

And finally, if you are trying to convert your application to be reactive, it is wise to use the Mongo driver with native support for reactive streams: https://docs.mongodb.com/drivers/reactive-streams/

Answered By - knittl
Answer Checked By - Mary Flores (JavaFixing Volunteer)