Java Futures

Bridge gaps and help overcome inconveniences with CompletableFuture.

Status

Overview

• requires Java 8
• methods that collect the results of multiple completion stages into a List future, both with short-circuit semantics (fail early if an input completion stage fails) and without (guaranteed not to be completed while there are uncompleted input stages)
• equivalent methods for supplyAsync, thenApply, thenCompose, etc. that accept functions throwing checked exceptions
• method similar to Scala’s Promise#completeWith
• method for unwrapping CompletionException
• method for exception mapping
• methods for dealing with asynchronous “try-with-resources” scenarios
• tests have virtually full code coverage

License

Revised BSD (3-Clause) License

Binary Releases

Published releases (compiled for Java 8 and up) are available on Maven Central.

<dependency>
    <groupId>net.florianschoppmann.java</groupId>
    <artifactId>java-futures</artifactId>
    <version>1.1.0</version>
</dependency>

Documentation

For current snapshot:

• API documentation
• Maven-generated project documentation

Release documentation is available by replacing “snapshot” in the URL by the respective version number (such as “1.1.0”).

Usage Examples

The following examples show some use cases of class Futures provided by this project.

Collect the results of multiple completion stages into a List future

CompletableFuture<Integer> sum(Set<CompletionStage<Integer>> set) {
    return Futures.shortCircuitCollect(set)
        .thenApply(list -> list.stream().mapToInt(Integer::intValue).sum());
}

Equivalent methods allowing for checked exceptions

CompletableFuture<Long> fileSize(CompletionStage<Path> filePathStage,
        Executor executor) {
    // Note that Files#size(Path) throws an IOException, hence it would have to
    // be wrapped in the lambda expression passed to
    // CompletionStage#thenApply(Function).
    return Futures.thenApplyAsync(filePathStage, Files::size, executor);
}