### Combine Multiple Java CompletionStages with Arbitrary Types

Source: https://github.com/spotify/completable-futures/blob/master/README.md

Demonstrates how to combine an arbitrary number of `CompletionStage` instances of different types using the `combine` method. This approach is safer than `join()` as it prevents accidental misuse by throwing an `IllegalArgumentException` if an uncombined future is accessed. Includes an example of dereferencing the combined future.

```Java
CompletionStage<String> f1;
CompletionStage<String> f2;
CompletionStage<String> result = combine(combined -> combined.get(f1) + combined.get(f2), f1, f2);
```

```Java
CompletionStage<String> f1;
CompletionStage<String> f2;
CompletionStage<String> result = dereference(combine(combined -> completedFuture(combined.get(f1) + combined.get(f2)), f1, f2));
```

--------------------------------

### Asynchronously Supply and Compose Java CompletionStages (supplyAsyncCompose)

Source: https://github.com/spotify/completable-futures/blob/master/README.md

Details `supplyAsyncCompose`, a utility similar to `CompletableFuture.supplyAsync`. When the provided `Supplier` returns a `CompletionStage`, `supplyAsyncCompose` automatically unwraps the resulting `CompletionStage<CompletionStage<T>>` to a `CompletionStage<T>`, streamlining asynchronous supply operations that produce futures.

```Java
CompletionStage<String> suppliedStage = completedFuture("hello").thenApply(stage -> stage + "-chained");
CompletionStage<String> outputStage = CompletableFutures.supplyAsyncCompose(suppliedStage);
```

--------------------------------

### Combine Map of Key-Value Futures with allAsMap in Java

Source: https://github.com/spotify/completable-futures/blob/master/README.md

The `CompletableFutures.allAsMap` method joins a map where keys are strings and values are `CompletableFuture` instances of a uniform type. It returns a single `CompletableFuture` that completes to a `Map` containing all the key-value pairs from the input futures once they all complete successfully.

```Java
  Map<String, CompletableFuture<String>> futures = new HashMap() {{
    put("key", completedFuture("value"));
  }};
  CompletableFuture<Map<String, String>> joined = CompletableFutures.allAsMap(futures);
```

--------------------------------

### Unwrap Nested Java CompletionStages (dereference)

Source: https://github.com/spotify/completable-futures/blob/master/README.md

Shows how to use `dereference` to flatten a nested `CompletionStage<CompletionStage<T>>` into a single `CompletionStage<T>`. This utility simplifies working with futures that resolve to other futures, making the asynchronous flow more manageable.

```Java
CompletionStage<CompletionStage<String>> wrapped = completedFuture(completedFuture("hello"));
CompletionStage<String> unwrapped = CompletableFutures.dereference(wrapped);
```

--------------------------------

### Combine List of Uniform Futures with allAsList in Java

Source: https://github.com/spotify/completable-futures/blob/master/README.md

The `CompletableFutures.allAsList` method joins a list of `CompletableFuture` instances of the same type. It returns a single `CompletableFuture` that completes to a `List` containing all the values from the input futures once they all complete successfully.

```Java
List<CompletableFuture<String>> futures = asList(completedFuture("a"), completedFuture("b"));
CompletableFuture<List<String>> joined = CompletableFutures.allAsList(futures);
```

--------------------------------

### Handle Java CompletionStage Results with Composition (handleCompose)

Source: https://github.com/spotify/completable-futures/blob/master/README.md

Explains `handleCompose`, a utility function similar to `CompletableFuture.handle`. Unlike `handle`, `handleCompose` allows returning a new `CompletionStage` instead of a direct value, enabling further asynchronous chaining based on the outcome (value or throwable) of the preceding stage.

```Java
CompletionStage<String> composed = handleCompose(future, (value, throwable) -> completedFuture("hello"));
```

--------------------------------

### Handle Java CompletionStage Exceptions with Composition (exceptionallyCompose)

Source: https://github.com/spotify/completable-futures/blob/master/README.md

Describes `exceptionallyCompose`, a utility function analogous to `CompletableFuture.exceptionally`. This method enables returning a new `CompletionStage` when an exception occurs in the preceding stage, providing a way to recover or chain with another asynchronous operation upon failure.

```Java
CompletionStage<String> composed = CompletableFutures.exceptionallyCompose(future, throwable -> completedFuture("fallback"));
```

--------------------------------

### Create Exceptionally Completed Java CompletableFutures

Source: https://github.com/spotify/completable-futures/blob/master/README.md

Demonstrates `exceptionallyCompletedFuture`, a utility method to create a `CompletableFuture` that is already completed with a specified exception. This is useful for immediately signaling a failure state without requiring an actual asynchronous computation to complete exceptionally.

```Java
return CompletableFutures.exceptionallyCompletedFuture(new RuntimeException("boom"));
```

--------------------------------

### Add Maven Dependency for completable-futures

Source: https://github.com/spotify/completable-futures/blob/master/README.md

To include the `completable-futures` library in a Maven project, add this dependency block to your `pom.xml` file. This library requires Java 8 and has no additional dependencies.

```XML
<dependency>
    <groupId>com.spotify</groupId>
    <artifactId>completable-futures</artifactId>
    <version>0.3.1</version>
</dependency>
```

--------------------------------

### Collect Stream of Futures into a Map with joinMap in Java

Source: https://github.com/spotify/completable-futures/blob/master/README.md

The `CompletableFutures.joinMap` is a `Stream` collector that applies an asynchronous operation to each stream element, associating the result with a key derived from the original element. This maintains the association between the input entity and its asynchronous operation's result, returning a `CompletableFuture<Map<K, V>>`.

```Java
collection.stream()
    .collect(joinMap(this::toKey, this::someAsyncFunc))
    .thenApply(this::consumeMap)
```

--------------------------------

### Collect Stream of Futures into a List with joinList in Java

Source: https://github.com/spotify/completable-futures/blob/master/README.md

The `CompletableFutures.joinList` is a `Stream` collector that aggregates multiple `CompletableFuture` instances into a single `CompletableFuture<List<T>>`. This is useful for applying an asynchronous operation to a collection of entities and then processing the combined results.

```Java
collection.stream()
    .map(this::someAsyncFunction)
    .collect(CompletableFutures.joinList())
    .thenApply(this::consumeList)
```

--------------------------------

### Combine Multiple Futures of Different Types with CompletableFutures.combine in Java

Source: https://github.com/spotify/completable-futures/blob/master/README.md

The `CompletableFutures.combine` method allows combining more than two `CompletableFuture` instances of potentially different types. It takes multiple futures and a function (bi-function, tri-function, etc.) to apply to their completed values, returning a new `CompletableFuture` with the result of the function.

```Java
CompletableFutures.combine(f1, f2, (a, b) -> a + b);
CompletableFutures.combine(f1, f2, f3, (a, b, c) -> a + b + c);
CompletableFutures.combine(f1, f2, f3, f4, (a, b, c, d) -> a + b + c + d);
CompletableFutures.combine(f1, f2, f3, f4, f5, (a, b, c, d, e) -> a + b + c + d + e);
```

--------------------------------

### Combine List of Futures with successfulAsList and Default Values in Java

Source: https://github.com/spotify/completable-futures/blob/master/README.md

Similar to `allAsList`, `CompletableFutures.successfulAsList` combines a list of futures. However, it handles failed futures by invoking a `defaultValueMapper` function for each failure, placing the returned default value in the result list instead of failing the joined future. This prevents the entire operation from failing if one future fails.

```Java
List<CompletableFuture<String>> input = asList(
    completedFuture("a"),
    exceptionallyCompletedFuture(new RuntimeException("boom")));
CompletableFuture<List<String>> joined = CompletableFutures.successfulAsList(input, t -> "default");
```

--------------------------------

### Poll External Resources into a Java CompletableFuture

Source: https://github.com/spotify/completable-futures/blob/master/README.md

Illustrates how to transform a long-running external task that only exposes a polling API into a `CompletableFuture`. The `CompletableFutures.poll` method repeatedly invokes a `Supplier` at a specified frequency until a result is available, converting the polling mechanism into a future-based operation.

```Java
Supplier<Optional<T>> pollingTask = () -> Optional.ofNullable(resource.result());
Duration frequency = Duration.ofSeconds(2);
CompletableFuture<T> result = CompletableFutures.poll(pollingTask, frequency, executor);
```

--------------------------------

### Combine Multiple Futures into a New Future with CompletableFutures.combineFutures in Java

Source: https://github.com/spotify/completable-futures/blob/master/README.md

The `CompletableFutures.combineFutures` method is similar to `combine`, but its mapping function returns another `CompletableFuture`. This is useful for chaining asynchronous operations where the combination logic itself produces a future, allowing for more complex asynchronous workflows.

```Java
CompletableFutures.combineFutures(f1, f2, (a, b) -> completedFuture(a + b));
CompletableFutures.combineFutures(f1, f2, f3, (a, b, c) -> completedFuture(a + b + c));
CompletableFutures.combineFutures(f1, f2, f3, f4, (a, b, c, d) -> completedFuture(a + b + c + d));
CompletableFutures.combineFutures(f1, f2, f3, f4, f5, (a, b, c, d, e) -> completedFuture(a + b + c + d + e));
```

=== COMPLETE CONTENT === This response contains all available snippets from this library. No additional content exists. Do not make further requests.