Transforming Data

Operators to modify, filter, and transform data flowing through streams.

Basic Transformations

// Map - synchronous transformation
Flux<Integer> numbers = Flux.range(1, 5)
    .map(n -> n * 2); // [2, 4, 6, 8, 10]

// FlatMap - asynchronous transformation
Flux<String> results = Flux.range(1, 3)
    .flatMap(n ->
        Mono.fromCallable(() -> fetchFromDatabase(n))
            .subscribeOn(Schedulers.boundedElastic())
    );

// Filter
Flux<Integer> evenNumbers = Flux.range(1, 10)
    .filter(n -> n % 2 == 0);

Complex Transformations

// concatMap (preserves order)
Flux<String> orderedResults = Flux.range(1, 3)
    .concatMap(n -> simulateAsync(n)); // Guaranteed order: 1, 2, 3

// switchMap (cancels previous)
Flux<String> searchResults = searchTermFlux
    .switchMap(term -> searchApi(term)); // Cancels previous search

// groupBy
Flux<GroupedFlux<Integer, String>> groups =
    Flux.just("apple", "banana", "cherry", "date")
        .groupBy(word -> word.length());

Transformation Pipeline

graph LR
    A[Source] --> B[Filter]
    B --> C[Map]
    C --> D[FlatMap]
    D --> E[Buffer]
    E --> F[Subscriber]

Common Operators:

• map: Transform each element
• filter: Keep only matching elements
• flatMap: Transform to new Publisher
• concatMap: Preserve order of results
• switchMap: Cancel previous operations