Annotates a CDI managed bean method to run asynchronously. The CDI managed bean must not be a Jakarta Enterprise Bean, and neither the method nor its class can be annotated with the MicroProfile Asynchronous annotation.

The Jakarta EE Product Provider runs the method on a ManagedExecutorService and returns to the caller a CompletableFuture that is backed by the same ManagedExecutorService to represent the execution of the method. The ManagedExecutorService is the default asynchronous execution facility for the CompletableFuture and and all dependent stages that are created from those, and so on, as defined by the ManagedExecutorService JavaDoc API. The Jakarta EE Product Provider makes this CompletableFuture available to the asynchronous method implementation via the Asynchronous.Result.getFuture and Asynchronous.Result.complete methods.

For example,

@Asynchronous
public CompletableFuture<Double> hoursWorked(LocalDate from, LocalDate to) {
    // Application component's context is made available to the async method,
    try (Connection con = ((DataSource) InitialContext.doLookup(
        "java:comp/env/jdbc/timesheetDB")).getConnection()) {
        ...
        return Asynchronous.Result.complete(total);
    } catch (NamingException | SQLException x) {
        throw new CompletionException(x);
    }
}

with usage,

hoursWorked(mon, fri).thenAccept(total -> {
    // Application component's context is made available to dependent stage actions,
    DataSource ds = InitialContext.doLookup(
        "java:comp/env/jdbc/payrollDB");
    ...
});

When the asynchronous method implementation returns a different CompletableFuture instance, the Jakarta EE Product Provider uses the completion of that instance to complete the CompletableFuture that the Jakarta EE Product Provider returns to the caller, completing it with the same result or exception.

For example,

@Asynchronous
public CompletableFuture<List<Itinerary>> findSingleLayoverFlights(Location source, Location dest) {
    try {
        ManagedExecutorService executor = InitialContext.doLookup(
            "java:comp/DefaultManagedExecutorService");

        return executor.supplyAsync(source::flightsFrom)
                       .thenCombine(executor.completedFuture(dest.flightsTo()),
                                    Itinerary::sourceMatchingDest);
    } catch (NamingException x) {
        throw new CompletionException(x);
    }
}

with usage,

findSingleLayoverFlights(RST, DEN).thenApply(Itinerary::sortByPrice);

Methods with the following return types can be annotated to be asynchronous methods:

• CompletableFuture
• CompletionStage
• void

The Jakarta EE Product Provider raises UnsupportedOperationException if other return types are used or if the annotation is placed at the class level. The injection target of ElementType.TYPE is to be used only by the CDI extension that is implemented by the Jakarta EE Product Provider to register the asynchronous method interceptor. Applications must only use the asynchronous method annotation at method level.

Exceptions that are raised by asynchronous methods are not raised directly to the caller because the method runs asynchronously to the caller. Instead, the CompletableFuture that represents the result is completed with the raised exception. Asynchronous methods are discouraged from raising checked exceptions because checked exceptions force the caller to write exception handling code that is unreachable. When a checked exception occurs, the asynchronous method implementation can flow the exception back to the resulting CompletableFuture either by raising a CompletionException with the original exception as the cause, or it can take the equivalent approach of exceptionally completing the CompletableFuture, using completeExceptionally to supply the original exception as the cause.

Except where otherwise stated, the Jakarta EE Product Provider raises RejectedExecutionException upon invocation of the asynchronous method if evident upfront that it cannot be accepted, for example if the JNDI name is not valid or points to something other than a managed executor resource. If determined at a later point that the asynchronous method cannot run (for example, if unable to establish thread context), then the Jakarta EE Product Provider completes the CompletableFuture exceptionally with CancellationException, and chains a cause exception if there is any.

The Jakarta EE Product Provider must assign the interceptor for asynchronous methods to have priority of Interceptor.Priority.PLATFORM_BEFORE + 5. Interceptors with a lower priority, such as Transactional, must run on the thread where the asynchronous method executes, rather than on the submitting thread. When an asynchronous method is annotated as Transactional, the transactional types which can be used are: TxType.REQUIRES_NEW, which causes the method to run in a new transaction, and TxType.NOT_SUPPORTED, which causes the method to run with no transaction. All other transaction attributes must result in UnsupportedOperationException upon invocation of the asynchronous method.

@Asynchronous
public CompletableFuture<Double> hoursWorked(LocalDateTime from, LocalDateTime to) {
    CompletableFuture<Double> future = Asynchronous.Result.getFuture();
    if (future.isDone())
        return future;

    try (Connection con = ((DataSource) InitialContext.doLookup(
        "java:comp/env/jdbc/timesheetDB")).getConnection()) {
        ...
        for (ResultSet result = stmt.executeQuery(); result.next() && !future.isDone(); )
            ...
        future.complete(total);
    } catch (NamingException | SQLException x) {
        future.completeExceptionally(x);
    }
    return future;
}