Completable Future Example for Multiple Parallel Requests and returning the first Response from them in Java.

FirstResponseMultipleParallelRequests.java

/**
An Example where we are calling 4 different Calls and returning the first response that we receive from any of these calls.
Please note this is not a working example, this is a sample code to give you a high level idea.
*/
//Here we create 4 Sample Futures
CompletableFuture<SearchResponse> aggregatorFuture1 = new CompletableFuture<>().supplyAsync(aggregator1.getSearchResult(request));
CompletableFuture<SearchResponse> aggregatorFuture2 = new CompletableFuture<>().supplyAsync(aggregator2.getSearchResult(request));
CompletableFuture<SearchResponse> aggregatorFuture3 = new CompletableFuture<>().supplyAsync(aggregator3.getSearchResult(request));
CompletableFuture<SearchResponse> aggregatorFuture4 = new CompletableFuture<>().supplyAsync(aggregator4.getSearchResult(request));

//Create the List of Above 4 Futures
List<CompletableFuture<String>> aggregatorFuturesList = Arrays.asList(aggregatorFuture1,aggregatorFuture2, aggregatorFuture3, aggregatorFuture4);

//Creating a new Future and using the anyOf() method which uses the list of futures
// that will Returing the first response from any of the 4 futures above
SearchResponse response = CompletableFuture.anyOf(aggregatorFuturesList)
.thenApply(r -> {
if (r instanceof SearchResponse) {
return (SearchResponse) r; //We need to type cast the response as well.
}
throw new Exception("Response type is not of SearchResponse!");
}).join();