java.util.concurrent · java.base · since Java 1.8

CompletableFuture

declaration

public class CompletableFuture<T>
        implements Future<T>, CompletionStage<T>

A composable promise: chain (thenApply/thenCompose), combine (thenCombine/allOf), recover (exceptionally), and time-bound (orTimeout) asynchronous work.

Key methods

`static CompletableFuture<T> supplyAsync(Supplier<T>, Executor)`	Start async work — ALWAYS pass your executor for blocking tasks.
`CompletableFuture<U> thenApply(Function<T,U>)`	Map the result.
`CompletableFuture<U> thenCompose(Function<T, CompletableFuture<U>>)`	FlatMap — chain dependent async calls.
`CompletableFuture<V> thenCombine(other, BiFunction)`	Zip two independent futures.
`static CompletableFuture<Void> allOf/anyOf(CompletableFuture<?>...)`	Fan-in.
`CompletableFuture<T> exceptionally(Function<Throwable,T>)`	Fallback on failure.
`CompletableFuture<T> orTimeout(long, TimeUnit)`	Fail with TimeoutException after the deadline (Java 9).
`T join()`	get() without checked exceptions (throws CompletionException).