Hands-On Reactive Programming in Spring 5

Collecting reactive sequences

It is possible to collect all elements in the list and process the resulting collection as a Mono stream with Flux.collectList() and Flux.collectSortedList(). The last one not only collects elements but also sorts them. Consider the following code:

Flux.just(1, 6, 2, 8, 3, 1, 5, 1)
    .collectSortedList(Comparator.reverseOrder())
    .subscribe(System.out::println);

This produces the following output with one collection containing sorted numbers:

[8, 6, 5, 3, 2, 1, 1, 1]

Note that collecting sequence elements in the collection may be resource hungry, especially when a sequence has many elements. Also, it is possible to consume all the available memory when trying to collect on an endless stream.

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