Home Map Mono<Resources<Resource<T>>> to Mono<List<T>>?
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Map Mono<Resources<Resource<T>>> to Mono<List<T>>?

Jan Nielsen
Jan Nielsen Published in 2018-01-13 01:40:16Z

In my reactive Java 9 Spring Boot 2 with Spring HATEOAS application, I have a REST API returning Mono<Resources<Resource<T>>>. In the application layer, I'd like the data to be Mono<List<T>> but how can I concisely map Mono<Resources<Resource<T>>> to Mono<List<T>>?

I was expecting something like:

public Mono<List<Order>> orders() {
    return rest.orders()
        .map(r -> r.getContent())

but this fails to compile because List does not define List.stream(Resources<Resource<Order>>. The rest.orders() returns Mono<Resources<Resource<Order>>>. Any ideas?

Jan Nielsen
Jan Nielsen Reply to 2018-01-14 14:28:22Z

A (memory-sloshing) solution:

public Mono<List<Order>> orders() {
    return rest.orders()
        .map(r -> toList(r));

private List<Order> toList(Resources<Resource<Order>> resources) {
    List<Order> orders = new ArrayList<>();
    resources.forEach(r -> orders.add(r.getContent());
    return orders;
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