supplyAsync

SupplyAsync is a static factory method of the CompletableFuture class in java.util.concurrent. It creates a new CompletableFuture that will be completed when the provided Supplier finishes executing in another thread. The computation is started asynchronously by submitting the supplier to an Executor.

The variant supplyAsync(Supplier<U> supplier) uses the ForkJoinPool.commonPool() as the default executor, while supplyAsync(Supplier<U> supplier, Executor executor) uses the supplied executor. The supplier is invoked once in that background thread, and the returned CompletableFuture<U> is completed with the supplier's result. If the supplier throws an exception, the CompletableFuture completes exceptionally with that exception.

Use cases include starting asynchronous computations without managing threads directly, enabling non-blocking programming patterns. The method returns immediately, allowing subsequent actions such as thenApply, thenAccept, thenCompose, whenComplete, or handle to be chained once the result is available.

Cancellation and error handling: The returned future can be canceled. If canceled before execution, the task may be prevented from running; if already running, cancellation depends on the executor and task responsiveness. Exceptions thrown by the supplier are captured and propagated to downstream stages as completion exceptions. When results are retrieved via get, ExecutionException typically wraps the original cause.

Origin and scope: Introduced in Java 8 as part of the CompletableFuture API, supplyAsync provides a concise means to initiate asynchronous work without explicit thread creation, fitting into asynchronous programming patterns common in modern Java applications.