Is it possible to chain async calls using Guava?

Question

I want to chain async rest service calls and have single callback when they finished.

Is it possible to do it with guava?

Answer 1

Futures.chain was removed in version 12.0. The new method of chaining together ListenableFutures is via the Futures.transform method.

https://github.com/google/guava/wiki/ListenableFutureExplained#application

From Guava latest javadoc (16.0.1 as of this writing).

ListenableFuture<RowKey> rowKeyFuture = indexService.lookUp(query);
AsyncFunction<RowKey, QueryResult> queryFunction =
   new AsyncFunction<RowKey, QueryResult>() {
   public ListenableFuture<QueryResult> apply(RowKey rowKey) {
      return dataService.read(rowKey);
   }
};
ListenableFuture<QueryResult> queryFuture = transform(rowKeyFuture, queryFunction);

Answer 2

You can use Futures.chain for chaining ListenableFutures:

final ListeningExecutorService service1 = MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(16));
final ListeningExecutorService service2 = MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(16));

ListenableFuture<String> service1result = service1.submit(new Callable<String>() {
    @Override
    public String call() throws Exception {
        return "service1result";
    }
});

ListenableFuture<String> service2result = Futures.chain(service1result, new Function<String, ListenableFuture<String>>() {
    @Override
    public ListenableFuture<String> apply(final @Nullable String input) {
        return service2.submit(new Callable<String>() {
            @Override
            public String call() throws Exception {
                return Joiner.on(" -> ").join(input, "service2result");
            }
        });
    }
});

System.out.format("Result: %s\r\n", service2result.get());

Output of at the code above in the terminal:

> run-main training.Training
[info] Compiling 1 Java source to /home/remeniuk/projects/guava-training/target/scala-2.9.1/classes...
[info] Running training.Training 
Result: service1result -> service2result